Chapter 27.
Field Function Definitions
You must select flow variables for a number of tasks in FLUENT. The
values are computed and placed in temporary memory that is allocated
for storing the results for each cell. For example, the Compute command associated with a panel that contains the field variable drop-down
list calculates the values of the selected function and places them into
temporary storage.
Sections 27.1 and 27.2 provide some general information related to the
field variables. In Section 27.3, the variables are listed by category in
Tables 27.3.1–27.3.14. These tables will also indicate when each variable
will be available. Section 27.4 contains an alphabetical listing of the
variables along with their definitions. All variables appear as they would
in the variable selection drop-down lists that are contained in many of
the FLUENT panels. Section 27.5 explains how you can calculate your
own field function.
• Section 27.1: Node and Cell Values
• Section 27.2: Velocity Reporting Options
• Section 27.3: Field Variables Listed by Category
• Section 27.4: Alphabetical Listing of Field Variables and Their
Definitions
• Section 27.5: Custom Field Functions
27.1
Node and Cell Values
Two types of field values are available for postprocessing: node values
and cell values. For the following discussion, “surface” refers to a collection of facets, lines or points that are created and manipulated in the
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27-1
Field Function Definitions
Surface menu. In most cases, these surfaces are created by computing
intersections of constant isovalues with the domain cells or with existing
surfaces.
27.1.1
Cell Values
FLUENT stores most variables in cells. For postprocessing, the entire
region contained within the cell has this value. A surface cell value is
the value of the cell that has been intersected by a surface facet or line, or
that contains a surface point. Since surface facets and lines are created
from the intersection of isovalues and the existing grid cells, this is a
unique definition. On a boundary, the cell value is the value in the cell
adjacent to the boundary.
27.1.2
Node Values
Node values are explicitly defined or obtained by averaging the cell data.
Various boundary conditions impose values of field variables at the domain boundaries, so grid node values on these boundary zones are defined
explicitly. In addition, for several variables (e.g., node coordinates) explicit node values are available at all nodes. For most variables, however,
the grid node values are computed by averaging the data of all the cells
that share the node.
Computation of node values is performed in two steps:
1. Values at all nodes are initialized to the average of the surrounding
cell values.
2. At boundaries, these node values are overwritten with the boundary values (if available). (Variables for which explicit node values
are available at boundaries are indicated by bnv in Tables 27.3.1–
27.3.14.)
For example, in Figure 27.1.1, the value at node n1 will be computed
from the average of the values in the surrounding cells (c1–c6), and the
value at node n2 will be the specified boundary value (not the average
27-2
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27.2 Velocity Reporting Options
c4
c3
c5
n1
c2
c6
c1
n2
c7
boundary
Figure 27.1.1: Computing Node Values
of the values in cells c1, c6, and c7), if there are explicit boundary values
available for the variable in question.
! Note that explicit boundary node values are not available for custom
field functions.
The values of the nodes on surfaces are interpolated from the grid node
data by linear interpolation. For zone surfaces the nodes on the surface
and the zone correspond, so the values are identical. For isofacets and
isolines, the values are interpolated from the grid nodes on the face
intersected by the isovalue. For isopoints, the value is interpolated from
all the grid nodes of the cell containing the point.
27.2
Velocity Reporting Options
The following methods are available for reporting velocities:
• Cartesian velocities: These velocities are based on the Cartesian
coordinate system used by the geometry. To report Cartesian velocities, select X Velocity, Y Velocity, or Z Velocity. This is the most
common type of velocity reported.
• Cylindrical velocities: These velocities are the axial, radial, and
tangential components based on the following coordinate systems:
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27-3
Field Function Definitions
– For axisymmetric problems, in which the rotation axis must
be the x axis, the x direction is the axial direction and the y
direction is the radial direction. (If you model axisymmetric
swirl, the swirl direction is the tangential direction.)
– For 2D problems involving a single cell zone, the z direction
is the axial direction, and its origin is specified in the Fluid
panel.
– For 3D problems involving a single cell zone, the coordinate
system is defined by the rotation axis and origin specified in
the Fluid panel.
– For problems involving multiple zones (e.g., multiple reference
frames or sliding meshes), the coordinate system is defined by
the rotation axis specified in the Fluid (or Solid) panel for the
“reference zone”. The reference zone is chosen in the Reference
Values panel, as described in Section 26.8. Recall that for 2D
problems, you will specify only the axis origin; the z direction
is always the axial direction.
For all of the above definitions of the cylindrical coordinate system,
positive radial velocities point radially out from the rotation axis,
positive axial velocities are in the direction of the rotation axis
vector, and positive tangential velocities are based on the righthand rule using the positive rotation axis.
To report cylindrical velocities, select Axial Velocity, Radial Velocity, etc. Figure 27.2.1 illustrates the cylindrical velocities available
for different types of domains: For 3D problems, you can report
axial, radial, and tangential velocities. For 2D problems, radial and
tangential velocities are available. For axisymmetric problems, you
can report axial and radial velocities, and if you are modeling axisymmetric swirl you can also report the swirl velocity (which is
equivalent to the tangential velocity).
• Relative velocities: These velocities are based on the coordinate
system and motion of a moving reference frame. They are useful
when you are modeling your flow using a rotating reference frame,
a mixing plane, multiple reference frames, or sliding meshes. (See
Chapter 9 for information about modeling flow in moving zones.)
27-4
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27.2 Velocity Reporting Options
axial
tangential
radial
tangential
radial
rotation
axis
rotation axis
origin
radial
rotation axis
axial
tangential
(swirl)
Figure 27.2.1: Cylindrical Velocity Components in 3D, 2D, and Axisymmetric Domains
To report relative velocities, select Relative X Velocity, Relative Y
Velocity, Relative Radial Velocity, etc. (Note that you can report
relative velocities for both Cartesian and cylindrical components.)
If you are using a single rotating reference frame, the relative velocity values will be reported with respect to the moving frame. If
you are using multiple reference frames, mixing planes, or sliding
meshes, you will need to specify the frame to which you want the
velocities to be relative by choosing the appropriate cell zone as
the Reference Zone in the Reference Values panel (see Section 26.8).
The axis of rotation for each cell zone is defined in the associated
Fluid panel or Solid panel. (See Section 6.17.1 or 6.18.1 for details.)
Note that if your problem does not involve any moving zones, relative and absolute velocities will be equivalent.
Note that relative velocities can also be used to compute stagnation
quantities (total pressure and total temperature), and that the cylindrical coordinate systems described in the second item above are used for
defining the Axial Coordinate and Radial Coordinate as well.
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Field Function Definitions
27.3
Field Variables Listed by Category
In Tables 27.3.1–27.3.14, the following restrictions apply to marked variables:
2d
2da
2dasw
3d
bnv
cpl
cv
dil
do
dpm
dtrm
e
edc
emm
ewt
gran
h2o
id
ke
kw
les
melt
mix
mp
nox
np
nv
p
p1
27-6
available only for 2D flows
available only for 2D axisymmetric flows (with or without swirl)
available only for 2D axisymmetric swirl flows
available only for 3D flows
node values available at boundaries
available only in the coupled solvers
available only for cell values (Node Values option turned off)
not available with full multicomponent diffusion
available only when the discrete ordinates radiation model is used
available only for coupled discrete phase calculations
available only when the discrete transfer radiation model is used
available only for energy calculations
available only with the EDC model for turbulence-chemistry
interaction
available only when the Eulerian multiphase model is used
available only with the enhanced wall treatment
available only if a granular phase is present
available only when the mixture contains water
available only when the ideal gas law is enabled for density
available only when one of the k- turbulence models is used
available only when one of the k-ω turbulence models is used
available only when the LES turbulence model is used
available only when the melting and solidification model is used
available only when the multiphase mixture model is used
available only for multiphase models
available only for NOx calculations
not available in parallel solvers
uses explicit node value function
available only in parallel solvers
available only when the P-1 radiation model is used
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27.3 Field Variables Listed by Category
pdf
pmx
ppmx
r
rad
rc
rsm
s2s
sa
seg
sp
sr
soot
stat
stcm
t
turbo
udm
uds
v
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
available
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
only
for non-premixed combustion calculations
for premixed combustion calculations
for partially premixed combustion calculations
when the Rosseland radiation model is used
for radiation heat transfer calculations
for finite-rate reactions
when the Reynolds stress turbulence model is used
when the surface-to-surface radiation model is used
when the Spalart-Allmaras turbulence model is used
in the segregated solver
for species calculations
for surface reactions
for soot calculations
with data sampling for unsteady statistics
for stiff chemistry calculations
for turbulent flows
when a turbomachinery topology has been defined
when a user-defined memory location is used
when a user-defined scalar is used
for viscous flows
Table 27.3.1: Pressure and Density Categories
Category
Pressure...
Density...
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Variable
Static Pressure (bnv, nv)
Pressure Coefficient
Dynamic Pressure
Absolute Pressure (bnv, nv)
Total Pressure (bnv, nv)
Relative Total Pressure
Density
Density of phase-n (mp)
Density All
27-7
Field Function Definitions
Table 27.3.2: Velocity Category
Category
Velocity...
27-8
Variable
Velocity Magnitude (bnv, nv)
X Velocity (bnv, nv)
Y Velocity (bnv, nv)
Z Velocity (3d, bnv, nv)
Swirl Velocity (2dasw, bnv, nv)
Axial Velocity (2da or 3d)
Radial Velocity
Stream Function (2d, nv)
Tangential Velocity
Mach Number (id)
Relative Velocity Magnitude (bnv, nv)
Relative X Velocity (bnv, nv)
Relative Y Velocity (bnv, nv)
Relative Z Velocity (3d, bnv, nv)
Relative Axial Velocity (2da)
Relative Radial Velocity (2da)
Relative Swirl Velocity (2dasw, bnv, nv)
Relative Tangential Velocity (2d or 3d)
Relative Mach Number (id)
Grid X-Velocity (nv)
Grid Y-Velocity (nv)
Grid Z-Velocity (3d, nv)
Velocity Angle
Relative Velocity Angle
Vorticity Magnitude (v)
Helicity (v, 3d)
X-Vorticity (v, 3d)
Y-Vorticity (v, 3d)
Z-Vorticity (v, 3d)
Cell Reynolds Number (v)
Preconditioning Reference Velocity (cpl)
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27.3 Field Variables Listed by Category
Table 27.3.3: Velocity Category (Multiphase-Specific Variables)
Category
Velocity...
Variable
phase-n Velocity Magnitude (mp)
phase-n X Velocity (mp)
phase-n Y Velocity (mp)
phase-n Z Velocity (3d, mp)
phase-n Axial Velocity (2da or 3d; mp)
phase-n Radial Velocity (mp)
phase-n Swirl Velocity (2dasw, mp, bnv, nv)
phase-n Stream Function (2d, mp, nv)
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Field Function Definitions
Table 27.3.4: Temperature, Radiation, and Solidification/Melting Categories
Category
Temperature...
Radiation...
Solidification/
Melting...
27-10
Variable
Static Temperature (e, nv)
Total Temperature (e, bnv, nv)
Enthalpy (e, nv)
Enthalpy of phase-n (e, nv, mp)
Total Enthalpy of phase-n (e, nv, mp)
Total Enthalpy Deviation of phase-n (e, nv, mp)
Total Energy of phase-n (e, nv, mp)
Relative Total Temperature (e)
Rothalpy (e, nv)
Fine Scale Temperature (edc, nv)
Wall Temperature (Outer Surface) (e, v, cv)
Wall Temperature (Inner Surface) (e, v, cv)
Total Enthalpy (e)
Total Enthalpy Deviation (e)
Entropy (e)
Total Energy (e)
Internal Energy (e)
Absorption Coefficient (r, p1, do, or dtrm)
Scattering Coefficient (r, p1, or do)
Refractive Index (do)
Radiation Temperature (p1 or do)
Incident Radiation (p1 or do)
Incident Radiation (Band n) (do (non-gray))
Surface Cluster ID (s2s)
Liquid Fraction (melt)
Contact Resistivity (melt)
X Pull Velocity (melt (if calculated))
Y Pull Velocity (melt (if calculated))
Z Pull Velocity (melt (if calculated), 3d)
Axial Pull Velocity (melt (if calculated), 2da)
Radial Pull Velocity (melt (if calculated), 2da)
Swirl Pull Velocity (melt (if calculated), 2dasw)
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27.3 Field Variables Listed by Category
Table 27.3.5: Turbulence Category
Category
Turbulence...
Variable
Turbulent Kinetic Energy (k) (ke, kw, or rsm; bnv, nv)
phase-n Turbulent Kinetic Energy (ke, emm)
UU Reynolds Stress (rsm)
VV Reynolds Stress (rsm)
WW Reynolds Stress (rsm)
UV Reynolds Stress (rsm)
UW Reynolds Stress (rsm, 3d)
VW Reynolds Stress (rsm, 3d)
Turbulence Intensity (ke, kw, or rsm)
Turbulent Dissipation Rate (Epsilon) (ke or rsm; bnv, nv)
phase-n Turbulent Dissipation Rate (ke, emm)
Specific Dissipation Rate (Omega) (kw)
Production of k (ke, kw, or rsm)
phase-n Production of k (ke, emm)
Modified Turbulent Viscosity (sa)
Turbulent Viscosity (t)
phase-n Turbulent Viscosity (t, emm)
Effective Viscosity (t)
Turbulent Viscosity Ratio (ke, kw, rsm, or sa)
Subgrid Turbulent Kinetic Energy (les)
Subgrid Turbulent Viscosity (les)
Subgrid Effective Viscosity (les)
Subgrid Turbulent Viscosity Ratio (les)
Effective Thermal Conductivity (t, e)
Effective Prandtl Number (t, e)
Wall Ystar (ke, kw, or rsm; cv)
Wall Yplus (t, cv)
phase-n Wall Yplus (t, cv, emm)
Turbulent Reynolds Number (Re y) (ke or rsm; ewt)
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Field Function Definitions
Table 27.3.6: Species, Reactions, Pdf, and Premixed Combustion Categories
Category
Species...
Reactions...
Pdf...
Premixed
Combustion...
27-12
Variable
Mass fraction of species-n (sp, pdf, or ppmx; nv)
Mole fraction of species-n (sp, pdf, or ppmx)
Concentration of species-n (sp, pdf, or ppmx)
Lam Diff Coef of species-n (sp, dil)
Eff Diff Coef of species-n (t, sp, dil)
Thermal Diff Coef of species-n (sp)
Enthalpy of species-n (sp)
species-n Source Term (rc, cpl)
Surface Deposition Rate of species-n (sr)
Relative Humidity (sp, pdf, or ppmx; h2o)
Time Step Scale (sp, stcm)
Fine Scale Mass fraction of species-n (edc)
Fine Scale Transfer Rate (edc)
1-Fine Scale Volume Fraction (edc)
Rate of Reaction-n (rc)
Arrhenius Rate of Reaction-n (rc)
Turbulent Rate of Reaction-n (rc, t)
Mean Mixture Fraction (pdf or ppmx; nv)
Secondary Mean Mixture Fraction (pdf or ppmx; nv)
Mixture Fraction Variance (pdf or ppmx; nv)
Secondary Mixture Fraction Variance (pdf or ppmx; nv)
Fvar Prod (pdf or ppmx)
Fvar2 Prod (pdf or ppmx)
Scalar Dissipation (pdf or ppmx)
Progress Variable (pmx or ppmx; nv)
Damkohler Number (pmx or ppmx)
Stretch Factor (pmx or ppmx)
Turbulent Flame Speed (pmx or ppmx)
Static Temperature (pmx or ppmx)
Product Formation Rate (pmx or ppmx)
Laminar Flame Speed (pmx or ppmx)
Critical Strain Rate (pmx or ppmx)
Adiabatic Flame Temperature (pmx or ppmx)
Unburnt Fuel Mass Fraction (pmx or ppmx)
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27.3 Field Variables Listed by Category
Table 27.3.7: NOx, Soot, and Unsteady Statistics Categories
Category
NOx...
Soot...
Unsteady Statistics...
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Variable
Mass fraction of NO (nox)
Mass fraction of HCN (nox)
Mass fraction of NH3 (nox)
Mole fraction of NO (nox)
Mole fraction of HCN (nox)
Mole fraction of NH3 (nox)
Concentration of NO (nox)
Concentration of HCN (nox)
Concentration of NH3 (nox)
Variance of Temperature (nox)
Variance of Species (nox)
Variance of Species 1 (nox)
Variance of Species 2 (nox)
Mass fraction of soot (soot)
Mass fraction of nuclei (soot)
Mean quantity-n (stat)
RMS quantity-n (stat)
27-13
Field Function Definitions
Table 27.3.8: Phases, Discrete Phase Model, Granular Pressure, and Granular Temperature Categories
Category
Phases...
Discrete Phase Model...
Granular Pressure...
Granular Temperature...
27-14
Variable
Volume fraction of phase-n (mp)
DPM Mass Source (dpm)
DPM Erosion (dpm, cv)
DPM Accretion (dpm, cv)
DPM X Momentum Source (dpm)
DPM Y Momentum Source (dpm)
DPM Z Momentum Source (dpm, 3d)
DPM Swirl Momentum Source (dpm, 2dasw)
DPM Sensible Enthalpy Source (dpm, e)
DPM Enthalpy Source (dpm, e)
DPM Absorption Coefficient (dpm, rad)
DPM Emission (dpm, rad)
DPM Scattering (dpm, rad)
DPM Burnout (dpm, sp, e)
DPM Evaporation/Devolatilization (dpm, sp, e)
DPM Concentration (dpm)
DPM species-n Source (dpm, sp, e)
phase-n Granular Pressure (emm, gran)
phase-n Granular Temperature (emm, gran)
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27.3 Field Variables Listed by Category
Table 27.3.9: Properties, Wall Fluxes, User Defined Scalars, and User Defined Memory Categories
Category
Properties...
Wall Fluxes...
User Defined Scalars...
User Defined Memory...
c Fluent Inc. November 28, 2001
Variable
Molecular Viscosity (v)
Molecular Viscosity of phase-n (v, mp)
Diameter of phase-n (mix or emm)
Thermal Conductivity (e, v)
Specific Heat (Cp) (e)
Specific Heat Ratio (gamma) (id)
Gas Constant (R) (id)
Molecular Prandtl Number (e, v)
Mean Molecular Weight (seg, pdf)
Sound Speed (id)
Wall Shear Stress (v, cv)
phase-n Wall Shear Stress (v, cv, emm)
X-Wall Shear Stress (v, cv)
Y-Wall Shear Stress (v, cv)
Z-Wall Shear Stress (v, 3d, cv)
phase-n X-Wall Shear Stress (v, cv, emm)
phase-n Y-Wall Shear Stress (v, cv, emm)
phase-n Z-Wall Shear Stress (v, 3d, cv, emm)
Axial-Wall Shear Stress (2da, cv)
Radial-Wall Shear Stress (2da, cv)
Swirl-Wall Shear Stress (2dasw, cv)
Skin Friction Coefficient (v, cv)
phase-n Skin Friction Coefficient (v, cv, emm)
Total Surface Heat Flux (e, v, cv)
Radiation Heat Flux (rad, cv)
Surface Incident Radiation (do, cv)
Surface Heat Transfer Coef. (e, v, cv)
Surface Nusselt Number (e, v, cv)
Surface Stanton Number (e, v, cv)
Scalar-n (uds, nv)
Diffusion Coef. of Scalar-n (uds)
udm-n (udm)
27-15
Field Function Definitions
Table 27.3.10: Cell Info, Grid, and Adaption Categories
Category
Cell Info...
Grid...
27-16
Variable
Cell Partition (np)
Active Cell Partition (p)
Stored Cell Partition (p)
Cell Id (p)
Cell Element Type
Cell Zone Type
Cell Zone Index
Partition Neighbors
X-Coordinate (nv)
Y-Coordinate (nv)
Z-Coordinate (3d, nv)
Axial Coordinate (nv)
Radial Coordinate (nv)
X Surface Area
Y Surface Area
Z Surface Area (3d)
X Face Area
Y Face Area
Z Face Area (3d)
Cell Equiangle Skew
Cell Equivolume Skew
Cell Volume
2D Cell Volume (2da)
Cell Wall Distance
Face Handedness
Face Squish Index
Cell Squish Index
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27.3 Field Variables Listed by Category
Table 27.3.11: Grid Category (Turbomachinery-Specific Variables) and
Adaption Category
Category
Grid...
Adaption...
Variable
Meridional Coordinate (nv, turbo)
Abs Meridional Coordinate (nv, turbo)
Spanwise Coordinate (nv, turbo)
Abs (H-C) Spanwise Coordinate (nv, turbo)
Abs (C-H) Spanwise Coordinate (nv, turbo)
Pitchwise Coordinate (nv, turbo)
Abs Pitchwise Coordinate (nv, turbo)
Adaption Function
Existing Value
Boundary Cell Distance
Boundary Normal Distance
Boundary Volume Distance (np)
Cell Volume Change
Cell Equiangle Skew
Cell Equivolume Skew
Cell Surface Area
Cell Warpage
Cell Children
Cell Refine Level
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27-17
Field Function Definitions
Table 27.3.12: Residuals Category
Category
Residuals...
27-18
Variable
Mass Imbalance
Pressure Residual (cpl)
X-Velocity Residual (cpl; 2d or 3d)
Y-Velocity Residual (cpl; 2d or 3d)
Z-Velocity Residual (cpl, 3d)
Axial-Velocity Residual (cpl, 2da)
Radial-Velocity Residual (cpl, 2da)
Swirl-Velocity Residual (cpl, 2dasw)
Temperature Residual (cpl, e)
Species-n Residual (cpl, sp)
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27.3 Field Variables Listed by Category
Table 27.3.13: Derivatives Category
Category
Derivatives...
c Fluent Inc. November 28, 2001
Variable
Strain Rate (v)
dX-Velocity/dx
dY-Velocity/dx
dZ-Velocity/dx (3d)
dAxial-Velocity/dx (2da)
dRadial-Velocity/dx (2da)
dSwirl-Velocity/dx (2dasw)
d species-n/dx (cpl, sp)
dX-Velocity/dy
dY-Velocity/dy
dZ-Velocity/dy (3d)
dAxial-Velocity/dy (2da)
dRadial-Velocity/dy (2da)
dSwirl-Velocity/dy (2dasw)
d species-n/dy (cpl, sp)
dX-Velocity/dz (3d)
dY-Velocity/dz (3d)
dZ-Velocity/dz (3d)
d species-n/dz (cpl, sp, 3d)
dOmega/dx (2dasw)
dOmega/dy (2dasw)
dp-dX (seg)
dp-dY (seg)
dp-dZ (seg, 3d)
27-19
Field Function Definitions
Table 27.3.14: Derivatives Category (Multiphase-Specific Variables)
Category
Derivatives...
27-20
Variable
Strain Rate of phase-n (v, emm)
phase-n dX-Velocity/dX (v, emm)
phase-n dY-Velocity/dX (v, emm)
phase-n dZ-Velocity/dX (v, emm, 3d)
phase-n dAxial-Velocity/dX (v, emm, 2da)
phase-n dRadial-Velocity/dX (v, emm, 2da)
phase-n dX-Velocity/dY (v, emm)
phase-n dY-Velocity/dY (v, emm)
phase-n dZ-Velocity/dY (v, emm, 3d)
phase-n dAxial-Velocity/dY (v, emm, 2da)
phase-n dRadial-Velocity/dY (v, emm, 2da)
phase-n dX-Velocity/dZ (v, emm, 3d)
phase-n dY-Velocity/dZ (v, emm, 3d)
phase-n dZ-Velocity/dZ (v, emm, 3d)
phase-n Granular Pressure G 0 cmpn (emm, gran)
phase-n Granular Pressure G 1 cmpn (emm, gran)
phase-n Granular Pressure G 2 cmpn (emm, gran, 3d)
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27.4 Alphabetical Listing of Field Variables and Their Definitions
27.4
Alphabetical Listing of Field Variables and Their
Definitions
Below, the variables listed in Tables 27.3.1–27.3.14 are defined. For
some variables (such as residuals) a general definition is given under the
category name, and variables in the category are not listed individually.
When appropriate, the unit quantity is included, as it appears in the
Quantities list in the Set Units panel.
Abs (C-H) Spanwise Coordinate (in the Grid... category) is the dimensional coordinate in the spanwise direction, from casing to hub. Its
unit quantity is length.
Abs (H-C) Spanwise Coordinate (in the Grid... category) is the dimensional coordinate in the spanwise direction, from hub to casing. Its
unit quantity is length.
Abs Meridional Coordinate (in the Grid... category) is the dimensional
coordinate that follows the flow path from inlet to outlet. Its unit
quantity is length.
Abs Pitchwise Coordinate (in the Grid... category) is the dimensional coordinate in the circumferential (pitchwise) direction. Its unit quantity is angle.
Absolute Pressure (in the Pressure... category) is equal to the operating
pressure plus the gauge pressure. See Section 7.12 for details. Its
unit quantity is pressure.
Absorption Coefficient (in the Radiation... category) is the property of a
medium that describes the amount of absorption of thermal radiation per unit path length within the medium. It can be interpreted
as the inverse of the mean free path that a photon will travel before
being absorbed (if the absorption coefficient does not vary along
the path). The unit quantity for Absorption Coefficient is lengthinverse.
Active Cell Partition (in the Cell Info... category) is an integer identifier
designating the partition to which a particular cell belongs. In
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27-21
Field Function Definitions
problems in which the grid is divided into multiple partitions to
be solved on multiple processors using the parallel version of FLUENT, the partition ID can be used to determine the extent of the
various groups of cells. The active cell partition is used for the current calculation, while the stored cell partition (the last partition
performed) is used when you save a case file. See Section 28.4.3 for
more information.
Adaption... includes field variables that are commonly used for adapting
the grid. For information about solution adaption, see Chapter 23.
Adaption Function (in the Adaption... category) is the undivided Laplacian of the values in temporary cell storage. For example, to display contours of the Laplacian of pressure, you first select Static
Pressure, click the Compute (or Display) button, select Adaption
Function, and finally click the Display button.
Adiabatic Flame Temperature (in the Premixed Combustion... category) is
the adiabatic temperature of burnt products in a laminar premixed
flame (Tb in Equation 15.2-21). Its unit quantity is temperature.
Arrhenius Rate of Reaction-n (in the Reactions... category) is given by
the following expression (see Equation 13.1-7 for definitions of the
variables shown here):

R̂r = Γ kf,r
Nr
Y
j=1
0
ηj,r
[Cj,r ]
− kb,r
Nr
Y

[Cj,r ]
00
ηj,r

j=1
The reported value is independent of any particular species, and
has units of kgmol/m3 -s.
To find the rate of production/destruction for a given species i due
to reaction r, multiply the reported reaction rate for reaction r by
00 −ν 0 ), where M is the molecular weight of species
the term Mi (νi,r
i
i,r
00 and ν 0 are the stoichiometric coefficients of species i in
i, and νi,r
i,r
reaction r.
Axial Coordinate (in the Grid... category) is the distance from the origin
in the axial direction. The axis origin and (in 3D) direction is
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27.4 Alphabetical Listing of Field Variables and Their Definitions
defined for each cell zone in the Fluid or Solid panel. The axial
direction for a 2D model is always the z direction, and the axial
direction for a 2D axisymmetric model is always the x direction.
The unit quantity for Axial Coordinate is length.
Axial Pull Velocity (in the Solidification/Melting... category) is the axialdirection component of the pull velocity for the solid material in a
continuous casting process. Its unit quantity is velocity.
Axial Velocity (in the Velocity... category) is the component of velocity in
the axial direction. (See Section 27.2 for details.) Its unit quantity
is velocity.
phase-n Axial Velocity (in the Velocity... category) is the component of
velocity in the axial direction for the nth phase. (The name of the
phase will replace phase-n). Its unit quantity is velocity.
Axial-Wall Shear Stress (in the Wall Fluxes... category) is the axial component of the force acting tangential to the surface due to friction.
Its unit quantity is pressure.
Boundary Cell Distance (in the Adaption... category) is an integer that
indicates the approximate number of cells from a boundary zone.
Boundary Normal Distance (in the Adaption... category) is the distance
of the cell centroid from the closest boundary zone.
Boundary Volume Distance (in the Adaption... category) is the cell volume distribution based on the Boundary Volume, Growth Factor,
and normal distance from the selected Boundary Zones defined in
the Boundary Adaption panel. See Section 23.3 for details.
Cell Children (in the Adaption... category) is a binary identifier based on
whether a cell is the product of a cell subdivision in the hangingnode adaption process (value = 1) or not (value = 0).
Cell Element Type (in the Cell Info... category) is the integer cell element
type identification number. Each cell can have one of the following
element types:
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Field Function Definitions
triangle
tetrahedron
quadrilateral
hexahedron
pyramid
wedge
1
2
3
4
5
6
Cell Equiangle Skew (in the Grid... and Adaption... categories) is a nondimensional parameter calculated using the normalized angle deviation method, and is defined as
max
where
qmax
qmin
qe
=
=
=
qmax − qe qe − qmin
,
180 − qe
qe
(27.4-1)
largest angle in the face or cell
smallest angle in the face or cell
angle for an equiangular face or cell
(e.g., 60 for a triangle and 90 for a square)
A value of 0 indicates a best case equiangular cell, and a value of
1 indicates a completely degenerate cell. Degenerate cells (slivers)
are characterized by nodes that are nearly coplanar (collinear in
2D). Cell Equiangle Skew applies to all elements.
Cell Equivolume Skew (in the Grid... and Adaption... categories) is a
nondimensional parameter calculated using the volume deviation
method, and is defined as
optimal-cell-size − cell-size
optimal-cell-size
(27.4-2)
where optimal-cell-size is the size of an equilateral cell with the
same circumradius. A value of 0 indicates a best case equilateral
cell and a value of 1 indicates a completely degenerate cell. Degenerate cells (slivers) are characterized by nodes that are nearly
coplanar (collinear in 2D). Cell Equivolume Skew applies only to
triangular and tetrahedral elements.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
Cell Id (in the Cell Info... category) is a unique integer identifier associated with each cell.
Cell Info... includes quantities that identify the cell and its relationship
to other cells.
Cell Partition (in the Cell Info... category) is an integer identifier designating the partition to which a particular cell belongs. In problems
in which the grid is divided into multiple partitions to be solved
on multiple processors using the parallel version of FLUENT, the
partition ID can be used to determine the extent of the various
groups of cells.
Cell Refine Level (in the Adaption... category) is an integer that indicates
the number of times a cell has been subdivided in the hanging node
adaption process, compared with the original grid. For example, if
one quad cell is split into four quads, the Cell Refine Level for each
of the four new quads will be 1. If the resulting four quads are
split again, the Cell Refine Level for each of the resulting 16 quads
will be 2.
Cell Reynolds Number (in the Velocity... category) is the value of the
Reynolds number in a cell. (Reynolds number is a dimensionless
parameter that is the ratio of inertia forces to viscous forces.) Cell
Reynolds Number is defined as
Re ≡
ρud
µ
(27.4-3)
where ρ is density, u is velocity magnitude, µ is the effective viscosity (laminar plus turbulent), and d is Cell Volume1/2 for 2D cases
and Cell Volume1/3 in 3D or axisymmetric cases.
Cell Squish Index (in the Grid... category) is a measure of the quality
of a mesh, and is calculated from the dot products of each vector
pointing from the centroid of a cell toward the center of each of its
faces, and the corresponding face area vector as
"
~ i · ~rc0/xf
A
i
max 1 −
~ i ||~rc0/xf |
i
|A
#
(27.4-4)
i
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Field Function Definitions
Therefore, the worst cells will have a Cell Squish Index close to 1.
Cell Surface Area (in the Adaption... category) is the total surface area
of the cell, and is computed by summing the area of the faces that
compose the cell.
Cell Volume (in the Grid... category) is the volume of a cell. In 2D the
volume is the area of the cell multiplied by the unit depth. For
axisymmetric cases, the cell volume is calculated using a reference
depth of 1 radian. The unit quantity of Cell Volume is volume.
2D Cell Volume (in the Grid... category) is the two-dimensional volume
of a cell in an axisymmetric computation. For an axisymmetric
computation, the 2D cell volume is scaled by the radius. Its unit
quantity is area.
Cell Volume Change (in the Adaption... category) is the maximum volume ratio of the current cell and its neighbors.
Cell Wall Distance (in the Grid... category) is the distribution of the normal distance of each cell centroid from the wall boundaries. Its
unit quantity is length.
Cell Warpage (in the Adaption... category) is the square root of the ratio
of the distance between the cell centroid and cell circumcenter and
the circumcenter radius:
s
warpage =
|~rcentroid − ~rcircumcenter |
Rcircumcenter
(27.4-5)
Cell Zone Index (in the Cell Info... category) is the integer cell zone identification number. In problems that have more than one cell zone,
the cell zone ID can be used to identify the various groups of cells.
Cell Zone Type (in the Cell Info... category) is the integer cell zone type
ID. A fluid cell has a type ID of 1, a solid cell has a type ID of 17,
and an exterior cell (parallel solver) has a type ID of 21.
Concentration of species-n (in the Species... category) is the mass per
unit volume of a species. Its unit quantity is density.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
Concentration of HCN, Concentration of NH3, Concentration of NO (in the
NOx... category) are the mass per unit volume of HCN, NH3 and
NO. The unit quantity for each is density. The Concentration of
HCN and the Concentration of NH3 will appear only if you are
modeling fuel NOx . See Section 17.1.5 for details.
Contact Resistivity (in the Solidification/Melting... category) is the additional resistance at the wall due to contact resistance. It is equal
to Rc (1 − β)/h, where Rc is the contact resistance, β is the liquid
fraction, and h is the cell height of the wall-adjacent cell. The unit
quantity for Contact Resistivity is thermal-resistivity.
Critical Strain Rate (in the Premixed Combustion... category) is a parameter that takes into account the stretching and extinction of
premixed flames (gcr in Equation 15.2-13). Its unit quantity is
time-inverse.
Custom Field Functions... are scalar field functions defined by you. You
can create a custom function using the Custom Field Function Calculator panel. All defined custom field functions will be listed in
the lower drop-down list. See Section 27.5 for details.
Damkohler Number (in the Premixed Combustion... category) is a nondimensional parameter that is defined as the ratio of turbulent to
chemical time scales.
Density... includes variables related to density.
Density (in the Density... category) is the mass per unit volume of the
fluid. Plots or reports of Density include only fluid cell zones. The
unit quantity for Density is density.
Density All (in the Density... category) is the mass per unit volume of
the fluid or solid material. Plots or reports of Density All include
both fluid and solid cell zones. The unit quantity for Density All is
density.
Density of phase-n (in the Density... category) is the mass per unit volume of the nth phase. Its unit quantity is density.
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Field Function Definitions
Derivatives... are the viscous derivatives. For example, dX-Velocity/dx
is the first derivative of the x component of velocity with respect
to the x-coordinate direction. You can compute first derivatives
of velocity, angular velocity, and pressure in the segregated solver,
and first derivatives of velocity, angular velocity, temperature, and
species in the coupled solvers.
Diameter of phase-n (in the Properties... category) is the diameter of particles, droplets, or bubbles of secondary phase n. Its unit quantity
is length.
Diffusion Coef. of Scalar-n (in the User Defined Scalars... category) is the
diffusion coefficient for the nth user-defined scalar transport equation. See the separate UDF manual for details about defining userdefined scalars.
Discrete Phase Model... includes quantities related to the discrete phase
model. See Chapter 19 for details about this model.
DPM Absorption Coefficient (in the Discrete Phase Model... category) is
the absorption coefficient for discrete-phase calculations that involve radiation (a in Equation 11.3-1). Its unit quantity is lengthinverse.
DPM Accretion (in the Discrete Phase Model... category) is the accretion
rate calculated at a wall boundary:
Raccretion =
N
X
ṁp
p=1
Aface
(27.4-6)
where ṁp is the mass flow rate of the particle stream, and Aface is
the area of the wall face where the particle strikes the boundary.
This item will appear only if the optional erosion/accretion model
is enabled. See Section 19.7.6 for details. The unit quantity for
DPM Accretion is mass-flux.
DPM Burnout (in the Discrete Phase Model... category) is the exchange
of mass from the discrete to the continuous phase for the combustion law (Law 5) and is proportional to the solid phase reaction
rate. The burnout exchange has units of mass-flow.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
DPM Concentration (in the Discrete Phase Model... category) is the total
concentration of the discrete phase. Its unit quantity is density.
DPM Emission (in the Discrete Phase Model... category) is the amount
of radiation emitted by a discrete-phase particle per unit volume.
Its unit quantity is heat-generation-rate.
DPM Enthalpy Source (in the Discrete Phase Model... category) is the
exchange of enthalpy (sensible enthalpy plus heat of formation)
from the discrete phase to the continuous phase. The exchange is
positive when the particles are a source of heat in the continuous
phase. The unit quantity for DPM Enthalpy Source is power.
DPM Erosion (in the Discrete Phase Model... category) is the erosion rate
calculated at a wall boundary face:
Rerosion =
N
X
ṁp f (α)
p=1
Aface
(27.4-7)
where ṁp is the mass flow rate of the particle stream, α is the
impact angle of the particle path with the wall face, f (α) is the
function specified in the Wall panel, and Aface is the area of the
wall face where the particle strikes the boundary. This item will
appear only if the optional erosion/accretion model is enabled. See
Section 19.7.6 for details. The unit quantity for DPM Erosion is
mass-flux.
DPM Evaporation/Devolatilization (in the Discrete Phase Model... category) is the exchange of mass, due to droplet-particle evaporation
or combusting-particle devolatilization, from the discrete phase to
the evaporating or devolatilizing species. If you are not using the
non-premixed combustion model, the mass source for each individual species (DPM species-n Source, below) is also available; for
non-premixed combustion, only this sum is available. The unit
quantity for DPM Evaporation/Devolatilization is mass-flow.
DPM Mass Source (in the Discrete Phase Model... category) is the total exchange of mass from the discrete phase to the continuous
phase. The mass exchange is positive when the particles are a
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Field Function Definitions
source of mass in the continuous phase. If you are not using the
non-premixed combustion model, DPM Mass Source will be equal
to the sum of all species mass sources (DPM species-n Source, below); if you are using the non-premixed combustion model, it will
be equal to DPM Burnout plus DPM Evaporation/Devolatilization.
The unit quantity for DPM Mass Source is mass-flow.
DPM Scattering (in the Discrete Phase Model... category) is the scattering coefficient for discrete-phase calculations that involve radiation
(σs in Equation 11.3-1). Its unit quantity is length-inverse.
DPM Sensible Enthalpy Source (in the Discrete Phase Model... category)
is the exchange of sensible enthalpy from the discrete phase to the
continuous phase. The exchange is positive when the particles are
a source of heat in the continuous phase. Its unit quantity is power.
DPM species-n Source (in the Discrete Phase Model... category) is the exchange of mass, due to droplet-particle evaporation or combustingparticle devolatilization, from the discrete phase to the evaporating or devolatilizing species. (The name of the species will replace
species-n in DPM species-n Source.) These species are specified in
the Set Injection Properties panel, as described in Section 19.9.5.
The unit quantity is mass-flow. Note that this variable will not be
available if you are using the non-premixed combustion model; use
DPM Evaporation/Devolatilization instead.
DPM Swirl Momentum Source (in the Discrete Phase Model... category)
is the exchange of swirl momentum from the discrete phase to the
continuous phase. This value is positive when the particles are a
source of momentum in the continuous phase. The unit quantity
is force.
DPM X, Y, Z Momentum Source (in the Discrete Phase Model... category) are the exchange of x-, y-, and z-direction momentum from
the discrete phase to the continuous phase. These values are positive when the particles are a source of momentum in the continuous
phase. The unit quantity is force.
Dynamic Pressure (in the Pressure... category) is defined as q ≡
Its unit quantity is pressure.
27-30
1
2
2 ρv .
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27.4 Alphabetical Listing of Field Variables and Their Definitions
Eff Diff Coef of species-n (in the Species... category) is the sum of the
laminar and turbulent diffusion coefficients of a species into the
mixture:
Di,m +
µt
ρSct
(The name of the species will replace species-n in Eff Diff Coef of
species-n.) The unit quantity is mass-diffusivity.
Effective Prandtl Number (in the Turbulence... category) is the ratio
µeff cp /keff , where µeff is the effective viscosity, cp is the specific
heat, and keff is the effective thermal conductivity.
Effective Thermal Conductivity (in the Properties... category) is the sum
of the laminar and turbulent thermal conductivities, k + kt , of the
fluid. A large thermal conductivity is associated with a good heat
conductor and a small thermal conductivity with a poor heat conductor (good insulator). Its unit quantity is thermal-conductivity.
Effective Viscosity (in the Turbulence... category) is the sum of the laminar and turbulent viscosities of the fluid. Viscosity, µ, is defined
by the ratio of shear stress to the rate of shear. Its unit quantity
is viscosity.
Enthalpy (in the Temperature... category) is defined differently for compressible and incompressible flows, and depending on the solver
and models in use.
For compressible flows,
H=
X
Yj H j
(27.4-8)
j
and for incompressible flows,
H=
X
j
Yj H j +
p
ρ
(27.4-9)
where Yj and Hj are, respectively, the mass fraction and enthalpy
of species j. (See Enthalpy of species-n, below). For the segregated
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Field Function Definitions
solver, the second term on the right-hand side of Equation 27.4-9
is included only if the pressure work term is included in the energy equation (see Section 11.2.1). For adiabatic non-premixed
combustion cases, Enthalpy reports the adiabatic value based on
the local mean mixture fraction. The unit quantity for Enthalpy is
specific-energy.
Enthalpy of phase-n (in the Temperature... category) is the enthalpy (defined above) of the nth phase. Its unit quantity is specific-energy.
Enthalpy of species-n (in the Species... category) is defined differently
depending on the solver and models options in use. The quantity:
Z
T
Hj =
Tref,j
cp,j dT + h0j (Tref,j )
(27.4-10)
where h0j (Tref,j ) is the formation enthalpy of species j at the reference temperature Tref,j ), is reported only for non-adiabatic PDF
cases, or if the coupled solver is selected. The quantity:
Z
T
hj =
cp,j dT
(27.4-11)
Tref
where Tref = 298.15K, is reported in all other cases. The unit
quantity for Enthalpy of species-n is specific-energy.
Entropy (in the Temperature... category) is a thermodynamic property
defined by the equation
∆S ≡
Z
rev
δQ
T
(27.4-12)
where “rev” indicates an integration along a reversible path connecting two states, Q is heat, and T is temperature. For compressible flows, entropy is computed using the equation
s = cv
27-32
p/pref
−1
(ρ/ρref )γ
(27.4-13)
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27.4 Alphabetical Listing of Field Variables and Their Definitions
where cv is computed from R/(γ − 1), and the reference pressure
and density are defined in the Reference Values panel. For incompressible flow, the entropy is computed using the equation
s = cp
T
−1
Tref
(27.4-14)
where cp is the specific heat at constant pressure and Tref is defined
in the Reference Values panel. The unit quantity for entropy is
specific-heat.
Existing Value (in the Adaption... category) is the value that presently
resides in the temporary space reserved for cell variables (i.e., the
last value that you displayed or computed).
Face Handedness (in the Grid... category) is a parameter that is equal
to one in cells that are adjacent to left-handed faces, and zero
elsewhere. It can be used to locate mesh problems.
Face Squish Index (in the Grid... category) is a measure of the quality
of a mesh, and is calculated from the dot products of each face
area vector, and the vector that connects the centroids of the two
adjacent cells as
1−
~ i · ~rc0/c1
A
~ i ||~rc0/c1 |
|A
(27.4-15)
Therefore, the worst cells will have a Face Squish Index close to 1.
Fine Scale Mass Fraction of species-n (in the Species... category) is the
term Yi∗ in Equation 13.1-30.
Fine Scale Temperature (in the Temperature... category) is the temperature of the fine scales, which is calculated from the enthalpy when
the reaction proceeds over the time scale (τ ∗ in Equation 13.1-29),
governed by the Arrhenius rates of Equation 13.1-7. Its unit quantity is temperature.
Fine Scale Transfer Rate (in the Species... category) is the transfer rate
of the fine scales, which is equal to the inverse of the time scale (τ ∗
in Equation 13.1-29). Its unit quantity is time-inverse.
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Field Function Definitions
1-Fine Scale Volume Fraction (in the Species... category) is a function
of the fine scale volume fraction (ξ ∗ in Equation 13.1-28). The
quantity is subtracted from unity to make it easier to interpret.
Fvar Prod (in the Pdf... category) is the production term in the mixture
fraction variance equation solved in the non-premixed combustion
model (i.e., the last two terms in Equation 14.1-5).
Fvar2 Prod (in the Pdf... category) is the production term in the secondary mixture fraction variance equation solved in the non-premixed
combustion model. See Equation 14.1-5.
Gas Constant (R) (in the Properties... category) is the gas constant of
the fluid. Its unit quantity is specific-heat.
Granular Pressure... includes quantities for reporting the solids pressure
for each granular phase.
phase-n Granular Pressure (in the Granular Pressure... category) is the
solids pressure for granular phase n (ps in Equation 20.4-45). See
Section 20.4.4 for details. Its unit quantity is pressure.
Granular Temperature... includes quantities for reporting the granular temperature for each granular phase.
phase-n Granular Temperature (in the Granular Temperature... category)
is the granular temperature for granular phase n (Θs in Equation 20.4-56). See Section 20.4.6 for details. Its unit quantity is
temperature.
Grid... includes variables related to the grid.
Grid X-Velocity, Grid Y-Velocity, Grid Z-Velocity (in the Velocity... category) are the vector components of the grid velocity for moving-grid
problems (rotating or multiple reference frames, mixing planes, or
sliding meshes). Its unit quantity is velocity.
Helicity (in the Velocity... category) is defined by the dot product of
vorticity and the velocity vector.
~)·V
~
H = (∇ × V
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(27.4-16)
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27.4 Alphabetical Listing of Field Variables and Their Definitions
It provides insight into the vorticity aligned with the fluid stream.
Vorticity is a measure of the rotation of a fluid element as it moves
in the flow field.
Incident Radiation (in the Radiation... category) is the total radiation
energy, G, that arrives at a location per unit time and per unit
area:
Z
G=
IdΩ
(27.4-17)
Ω=4π
where I is the radiation intensity and Ω is the solid angle. G
is the quantity that the P-1 radiation model computes. For the
DO radiation model, the incident radiation is computed over a
finite number of discrete solid angles, each associated with a vector
direction. The unit quantity for Incident Radiation is heat-flux.
Incident Radiation (Band n) (in the Radiation... category) is the radiation
energy contained in the wavelength band ∆λ for the non-gray DO
radiation model. Its unit quantity is heat-flux.
Internal Energy (in the Temperature... category) is the summation of the
kinetic and potential energies of the molecules of the substance (in
the absence of chemical or nuclear reactions) per unit volume. It
is defined as e = cv T . Its unit quantity is specific-energy.
Lam Diff Coef of species-n (in the Species... category) is the laminar diffusion coefficient of a species into the mixture, Di,m . Its unit quantity is mass-diffusivity.
Laminar Flame Speed (in the Premixed Combustion... category) is the
propagation speed of laminar premixed flames (Ul in Equation 15.2-4).
Its unit quantity is velocity.
Liquid Fraction (in the Solidification/Melting... category) is the liquid
fraction β computed by the solidification/melting model:
β=
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∆H
=0
L
if
T < Tsolidus
27-35
Field Function Definitions
β=
β=
∆H
=1
L
∆H
T − Tsolidus
=
L
Tliquidus − Tsolidus
if
T > Tliquidus
if
Tsolidus < T < Tliquidus
(27.4-18)
Mach Number (in the Velocity... category) is the ratio of velocity and
speed of sound.
Mass fraction of HCN, Mass fraction of NH3, Mass fraction of NO (in the
NOx... category) are the mass of HCN, the mass of NH3 , and the
mass of NO per unit mass of the mixture (e.g., kg of HCN in
1 kg of the mixture). The Mass fraction of HCN and the Mass
fraction of NH3 will appear only if you are modeling fuel NOx . See
Section 17.1.5 for details.
Mass fraction of nuclei (in the Soot... category) is the number of particles
per unit mass of the mixture (in units of particles ×1015 /kg) The
Mass fraction of nuclei will appear only if you use the two-step soot
model. See Section 17.2 for details.
Mass fraction of soot (in the Soot... category) is the mass of soot per
unit mass of the mixture (e.g., kg of soot in 1 kg of the mixture).
See Section 17.2 for details.
Mass fraction of species-n (in the Species... category) is the mass of a
species per unit mass of the mixture (e.g., kg of species in 1 kg of
the mixture).
Mean quantity-n (in the Unsteady Statistics... category) is the time-averaged value of a solution variable (e.g., Static Pressure). See Section 22.15.3 for details.
Meridional Coordinate (in the Grid... category) is the normalized (dimensionless) coordinate that follows the flow path from inlet to outlet.
Its value varies from 0 to 1.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
Mixture Fraction Variance (in the Pdf... category) is the variance of the
mixture fraction solved for in the non-premixed combustion model.
This is the second conservation equation (along with the mixture
fraction equation) that the non-premixed combustion model solves.
(See Section 14.1.2.)
Modified Turbulent Viscosity (in the Turbulence... category) is the transported quantity ν̃ that is solved for in the Spalart-Allmaras turbulence model (see Equation 10.3-1). The turbulent viscosity, µt , is
computed directly from this quantity using the relationship given
by Equation 10.3-2. Its unit quantity is viscosity.
Mole fraction of species-n (in the Species... category) is the number of
moles of a species in one mole of the mixture.
Mole fraction of HCN, Mole fraction of NH3, Mole fraction of NO (in the
NOx... category) are the number of moles of HCN, NH3 , and NO
in one mole of the mixture. The Mole fraction of HCN and the Mole
fraction of NH3 will appear only if you are modeling fuel NOx . See
Section 17.1.5 for details.
Molecular Prandtl Number (in the Properties...
cp µlam /klam .
category) is the ratio
Molecular Viscosity (in the Properties... category) is the laminar viscosity
of the fluid. Viscosity, µ, is defined by the ratio of shear stress to
the rate of shear. Its unit quantity is viscosity.
Molecular Viscosity of phase-n (in the Properties... category) is the laminar viscosity of the nth phase. Its unit quantity is viscosity.
NOx... contains quantities related to the NOx model. See Section 17.1
for details about this model.
Partition Boundary Cell Distance (in the Grid... category) is the smallest number of cells which must be traversed to reach the nearest
partition (interface) boundary.
Partition Neighbors (in the Cell Info... category) is the number of adjacent
partitions (i.e., those that share at least one partition boundary
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Field Function Definitions
face (interface)). It gives a measure of the number of messages
that will have to be generated for parallel processing.
Pdf... contains quantities related to the non-premixed combustion model,
which is described in Chapter 14.
Phases... contains quantities for reporting the volume fraction of each
phase. See Chapter 20 for details.
Pitchwise Coordinate (in the Grid... category) is the normalized (dimensionless) coordinate in the circumferential (pitchwise) direction. Its
value varies from 0 to 1.
Preconditioning Reference Velocity (in the Velocity... category) is the reference velocity used in the coupled solver’s preconditioning algorithm. See Section 22.4.2 for details.
Premixed Combustion... contains quantities related to the premixed combustion model, which is described in Chapter 15.
Pressure... includes quantities related to a normal force per unit area (the
impact of the gas molecules on the surfaces of a control volume).
Pressure Coefficient (in the Pressure... category) is a dimensionless parameter defined by the equation
Cp =
(p − pref )
qref
(27.4-19)
where p is the static pressure, pref is the reference pressure, and
qref is the reference dynamic pressure defined by 12 ρref vref 2 . The
reference pressure, density, and velocity are defined in the Reference
Values panel.
Product Formation Rate (in the Premixed Combustion... category) is the
source term in the progress variable transport equation (Sc in
Equation 15.2-1). Its unit quantity is time-inverse.
Production of k (in the Turbulence... category) is the rate of production
of turbulence kinetic energy (times density). Its unit quantity is
turb-kinetic-energy-production.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
phase-n Production of k (in the Turbulence... category) is the rate of production of turbulent kinetic energy (times density) for the nth
phase. Its unit quantity is turb-kinetic-energy-production.
Progress Variable (in the Premixed Combustion... category) is a normalized mass fraction of the combustion products (c = 1) or unburnt
mixture products (c = 0), as defined by Equation 15.2-2.
Properties... includes material property quantities for fluids and solids.
Radial Coordinate (in the Grid... category) is the length of the radius vector in the polar coordinate system. The radius vector is defined by
a line segment between the node and the axis of rotation. You can
define the rotational axis in the Fluid panel. (See also Section 27.2.)
The unit quantity for Radial Coordinate is length.
Radial Pull Velocity (in the Solidification/Melting... category) is the radialdirection component of the pull velocity for the solid material in a
continuous casting process. Its unit quantity is velocity.
Radial Velocity (in the Velocity... category) is the component of velocity
in the radial direction. (See Section 27.2 for details.) The unit
quantity for Radial Velocity is velocity.
phase-n Radial Velocity (in the Velocity... category) is the component of
velocity in the radial direction for the nth phase. Its unit quantity
is velocity.
Radial-Wall Shear Stress (in the Wall Fluxes... category) is the radial
component of the force acting tangential to the surface due to friction. Its unit quantity is pressure.
Radiation... includes quantities related to radiation heat transfer. See
Section 11.3 for details about the radiation models available in
FLUENT.
Radiation Heat Flux (in the Wall Fluxes... category) is the rate of radiation heat transfer through the control surface. It is calculated by
the solver according to the specified radiation model. Heat flux
out of the domain is negative, and heat flux into the domain is
positive. The unit quantity for Radiation Heat Flux is heat-flux.
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Field Function Definitions
Radiation Temperature (in the Radiation... category) is the quantity θR ,
defined by
θR = (
G 1/4
)
4σ
(27.4-20)
where G is the Incident Radiation. The unit quantity for Radiation
Temperature is temperature.
Rate of Reaction-n (in the Reactions... category) is the effective rate of
progress of nth reaction. For the finite-rate model, the value is the
same as the Arrhenius Rate of Reaction-n. For the eddy-dissipation
model, the value is equivalent to the Turbulent Rate of Reaction-n.
For the finite-rate/eddy-dissipation model, it is the lesser of the
two.
Reactions... includes quantities related to finite-rate reactions. See Chapter 13 for information about modeling finite-rate reactions.
Refractive Index (in the Radiation... category) is a nondimensional parameter defined as the ratio of the speed of light in a material to
that in vacuum. See Section 11.3.6 for details.
Relative Axial Velocity (in the Velocity... category) is the axial-direction
component of the velocity relative to the reference frame motion.
See Section 27.2 for details. The unit quantity for Relative Axial
Velocity is velocity.
Relative Humidity (in the Species... category) is the ratio of the partial pressure of the water vapor actually present in an air-water
mixture to the saturation pressure of water vapor at the mixture
temperature. FLUENT computes the saturation pressure, p, from
the following equation [190]:
p
ln
pc
27-40
=
8
X
Tc
Fi [a (T − Tp )]i−1
−1 ×
T
i=1
(27.4-21)
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27.4 Alphabetical Listing of Field Variables and Their Definitions
where
pc
Tc
F1
F2
F3
F4
F5
F6
F7
F8
a
Tp
=
=
=
=
=
=
=
=
=
=
=
=
22.089 MPa
647.286 K
−7.4192420
2.9721000 × 10−1
−1.1552860 × 10−1
8.6856350 × 10−3
1.0940980 × 10−3
−4.3999300 × 10−3
2.5206580 × 10−3
−5.2186840 × 10−4
0.01
338.15 K
Relative Mach Number (in the Velocity... category) is the nondimensional
ratio of the relative velocity and speed of sound.
Relative Radial Velocity (in the Velocity... category) is the radial-direction
component of the velocity relative to the reference frame motion.
(See Section 27.2 for details.) The unit quantity for Relative Radial
Velocity is velocity.
Relative Swirl Velocity (in the Velocity... category) is the tangential-direction component of the velocity relative to the reference frame motion, in an axisymmetric swirling flow. (See Section 27.2 for details.) The unit quantity for Relative Swirl Velocity is velocity.
Relative Tangential Velocity (in the Velocity... category) is the tangentialdirection component of the velocity relative to the reference frame
motion. (See Section 27.2 for details.) The unit quantity for Relative Tangential Velocity is velocity.
Relative Total Pressure (in the Pressure... category) is the stagnation
pressure computed using relative velocities instead of absolute velocities; i.e., for incompressible flows the dynamic pressure would
be computed using the relative velocities. (See Section 27.2 for
more information about relative velocities.) The unit quantity for
Relative Total Pressure is pressure.
Relative Total Temperature (in the Temperature... category) is the stagnation temperature computed using relative velocities instead of
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Field Function Definitions
absolute velocities. (See Section 27.2 for more information about
relative velocities.) The unit quantity for Relative Total Temperature is temperature.
Relative Velocity Angle (in the Velocity... category) is similar to the Velocity Angle except that it uses the relative tangential velocity, and
is defined as
tan−1 −
relative-tangential-velocity
axial-velocity
(27.4-22)
Its unit quantity is angle.
Relative Velocity Magnitude (in the Velocity... category) is the magnitude
of the relative velocity vector instead of the absolute velocity vector. The relative velocity (w)
~ is the difference between the absolute
velocity (~v ) and the grid velocity. For simple rotation, the relative
velocity is defined as
~ × ~r
w
~ ≡ ~v − Ω
(27.4-23)
~ is the angular velocity of a rotating reference frame about
where Ω
the origin and ~r is the position vector. (See also Section 27.2.) The
unit quantity for Relative Velocity Magnitude is velocity.
Relative X Velocity, Relative Y Velocity, Relative Z Velocity (in the Velocity... category) are the x-, y-, and z-direction components of the
velocity relative to the reference frame motion. (See Section 27.2
for details.) The unit quantity for these variables is velocity.
Residuals... contains different quantities for the segregated and coupled
solvers:
In the coupled solvers, this category includes the corrections to the
primitive variables pressure, velocity, temperature, and species, as
well as the time rate of change of the corrections to these primitive variables for the current iteration (i.e., residuals). Corrections
are the changes in the variables between the current and previous
iterations and residuals are computed by dividing a cell’s correction by its physical time step. The total residual for each variable
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27.4 Alphabetical Listing of Field Variables and Their Definitions
is the summation of the Euler, viscous, and dissipation contributions. The dissipation components are the vector components of
the flux-like, face-based dissipation operator.
In the segregated solver, only the Mass Imbalance in each cell is
reported (unless you have requested others, as described in Section 22.16.1). At convergence, this quantity should be small compared to the average mass flow rate.
RMS quantity-n (in the Unsteady Statistics... category) is the root mean
squared value of a solution variable (e.g., Static Pressure). See
Section 22.15.3 for details.
Rothalpy (in the Temperature... category) is defined as
I =h+
w 2 u2
−
2
2
(27.4-24)
where h is the enthalpy, w is the relative velocity magnitude, and
u is the magnitude of the rotational velocity ~u = ~ω × ~r.
Scalar-n (in the User Defined Scalars... category) is the value of the
nth scalar quantity you have defined as a user-defined scalar. See
the separate UDF manual for more information about user-defined
scalars.
Scalar Dissipation (in the Pdf... category) is one of two parameters that
describes the species mass fraction and temperature for a laminar
flamelet in mixture fraction spaces. It is defined as
χ = 2D|∇f |2
(27.4-25)
where f is the mixture fraction and D is a representative diffusion
coefficient (see Section 14.4.3 for details). Its unit quantity is timeinverse.
Scattering Coefficient (in the Radiation... category) is the property of a
medium that describes the amount of scattering of thermal radiation per unit path length for propagation in the medium. It can
be interpreted as the inverse of the mean free path that a photon
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Field Function Definitions
will travel before undergoing scattering (if the scattering coefficient
does not vary along the path). The unit quantity for Scattering Coefficient is length-inverse.
Secondary Mean Mixture Fraction (in the Pdf... category) is the mean
ratio of the secondary stream mass fraction to the sum of the fuel,
secondary stream, and oxidant mass fractions. It is the secondarystream conserved scalar that is calculated by the non-premixed
combustion model. See Section 14.1.2.
Secondary Mixture Fraction Variance (in the Pdf... category) is the variance of the secondary stream mixture fraction that is solved for in
the non-premixed combustion model. See Section 14.1.2.
Skin Friction Coefficient (in the Wall Fluxes... category) is a nondimensional parameter defined as the ratio of the wall shear stress and
the reference dynamic pressure
Cf ≡
τw
1
2
2 ρref vref
(27.4-26)
where τw is the wall shear stress, and ρref and vref are the reference
density and velocity defined in the Reference Values panel.
phase-n Skin Friction Coefficient (in the Wall Fluxes... category) is the
skin friction coefficient (defined above) for the nth phase.
Solidification/Melting... contains quantities related to solidification and
melting.
Soot... contains quantities related to the Soot model, which is described
in Section 17.2.
Sound Speed (in the Properties...
category) is the acoustic speed. It is
q
γp
computed from
ρ . Its unit quantity is velocity.
Spanwise Coordinate (in the Grid... category) is the normalized (dimensionless) coordinate in the spanwise direction, from hub to casing.
Its value varies from 0 to 1.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
species-n Source Term (in the Species... category) is the source term in
each of the species transport equations due to reactions. The unit
quantity is always kg/m3 -s.
Species... includes quantities related to species transport and reactions.
Specific Dissipation Rate (Omega) (in the Turbulence... category) is the
rate of dissipation of turbulence kinetic energy in unit volume and
time. Its unit quantity is time-inverse.
Specific Heat (Cp) (in the Properties... category) is the thermodynamic
property of specific heat at constant pressure. It is defined as the
rate of change of enthalpy with temperature while pressure is held
constant. Its unit quantity is specific-heat.
Specific Heat Ratio (gamma) (in the Properties... category) is the ratio
of specific heat at constant pressure to the specific heat at constant
volume.
Stored Cell Partition (in the Cell Info... category) is an integer identifier
designating the partition to which a particular cell belongs. In
problems in which the grid is divided into multiple partitions to
be solved on multiple processors using the parallel version of FLUENT, the partition ID can be used to determine the extent of the
various groups of cells. The active cell partition is used for the current calculation, while the stored cell partition (the last partition
performed) is used when you save a case file.See Section 28.4.3 for
more information.
Static Pressure (in the Pressure... category) is the static pressure of the
fluid. It is a gauge pressure expressed relative to the prescribed
operating pressure. The absolute pressure is the sum of the Static
Pressure and the operating pressure. Its unit quantity is pressure.
Static Temperature (in the Temperature... and Premixed Combustion...
categories) is the temperature that is measured moving with the
fluid. Its unit quantity is temperature.
Note that Static Temperature will appear in the Premixed Combustion... category only for adiabatic premixed combustion calculations. See Section 15.3.7.
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Field Function Definitions
Strain Rate (in the Derivatives... category) relates shear stress to the viscosity. Also called the shear rate (γ̇ in Equation 7.3-17), the strain
rate is related to the second invariant of the rate-of-deformation
tensor D. Its unit quantity is time-inverse. In 3D Cartesian coordinates, the strain rate, S, is defined as
S2 =
∂u ∂u ∂u
∂u ∂u ∂v
∂u ∂u ∂w
+
+
+
+
+
+
∂x ∂x ∂x
∂y ∂y
∂x
∂z ∂z
∂x
∂v ∂v
∂v ∂v ∂v
∂v ∂v ∂w
∂u
+
+
+
+
+
+
∂x ∂x ∂y
∂y ∂y ∂y
∂z ∂z
∂y
∂w ∂w ∂u
∂w ∂w ∂v
∂w ∂w ∂w
+
+
+
+
+
∂x ∂x
∂z
∂y ∂y
∂z
∂z ∂z
∂z
(27.4-27)
Strain Rate of phase-n (in the Derivatives... category) is the strain rate
(defined above) of the nth phase. Its unit quantity is time-inverse.
Stream Function (in the Velocity... category) is formulated as a relation
between the streamlines and the statement of conservation of mass.
A streamline is a line that is tangent to the velocity vector of the
flowing fluid. For a 2D planar flow, the stream function, ψ, is
defined such that
∂ψ
∂ψ
ρu ≡
ρv ≡ −
(27.4-28)
∂y
∂x
where ψ is constant along a streamline and the difference between
constant values of stream function defining two streamlines is the
mass rate of flow between the streamlines.
The accuracy of the stream function calculation is determined by
the text command /display/set/n-stream-func.
Stretch Factor (in the Premixed Combustion... category) is a nondimensional parameter that is defined as the probability of unquenched
flamelets (G in Equation 15.2-10).
Subgrid Turbulent Kinetic Energy (in the Turbulence... category) is the
turbulence kinetic energy per unit mass of the unresolved eddies,
ks , calculated using the LES turbulence model. It is defined as
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27.4 Alphabetical Listing of Field Variables and Their Definitions
ks =
νt2
L2s
(27.4-29)
Its unit quantity is turbulent-kinetic-energy.
Subgrid Turbulent Viscosity (in the Turbulence... category) is the turbulent (dynamic) viscosity of the fluid calculated using the LES
turbulence model. It expresses the proportionality between the
anisotropic part of the subgrid-scale stress tensor and the rate-ofstrain tensor. (See Equation 10.7-7.) Its unit quantity is viscosity.
Subgrid Turbulent Viscosity Ratio (in the Turbulence... category) is the
ratio of the subgrid turbulent viscosity of the fluid to the laminar
viscosity, calculated using the LES turbulence model.
Surface Cluster ID (in the Radiation... category) is used to view the distribution of surface clusters in the domain. Each cluster has a
unique integer number (ID) associated with it.
Surface Deposition Rate of species-n (in the Species... category) is the
amount of a surface species that is deposited on the substrate. Its
unit quantity is mass-flux.
Surface Heat Transfer Coef. (in the Wall Fluxes... category) is defined by
the equation
q
heff =
(27.4-30)
Twall − Tref
where q is the convective heat flux, Twall is the wall temperature,
and Tref is reference temperature defined in the Reference Values
panel. Its unit quantity is heat-transfer-coefficient.
Surface Incident Radiation (in the Wall Fluxes... category) is the net incoming radiation heat flux on a surface. Its unit quantity is heatflux.
Surface Nusselt Number (in the Wall Fluxes... category) is a local nondimensional coefficient of heat transfer defined by the equation
Nu =
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heff Lref
k
(27.4-31)
27-47
Field Function Definitions
where heff is the heat transfer coefficient, Lref is the reference length
defined in the Reference Values panel, and k is the molecular thermal conductivity.
Surface Stanton Number (in the Wall Fluxes... category) is a nondimensional coefficient of heat transfer defined by the equation
St =
heff
ρref vref cp
(27.4-32)
where heff is the heat transfer coefficient, ρref and vref are reference
values of density and velocity defined in the Reference Values panel,
and cp is the specific heat at constant pressure.
Swirl Pull Velocity (in the Solidification/Melting... category) is the tangential-direction component of the pull velocity for the solid material
in a continuous casting process. Its unit quantity is velocity.
Swirl Velocity (in the Velocity... category) is the tangential-direction
component of the velocity in an axisymmetric swirling flow. See
Section 27.2 for details. The unit quantity for Swirl Velocity is
velocity.
phase-n Swirl Velocity (in the Velocity... category) is the tangential-direction component of the velocity in an axisymmetric swirling flow for
the nth phase. Its unit quantity is velocity.
Swirl-Wall Shear Stress (in the Wall Fluxes... category) is the swirl component of the force acting tangential to the surface due to friction.
Its unit quantity is pressure.
Tangential Velocity (in the Velocity... category) is the velocity component
in the tangential direction. (See Section 27.2 for details.) The unit
quantity for Tangential Velocity is velocity.
Temperature... indicates the quantities associated with the thermodynamic temperature of a material.
Thermal Conductivity (in the Properties... category) is a parameter (k)
that defines the conduction rate through a material via Fourier’s
law (q = −k∇T ). A large thermal conductivity is associated with
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27.4 Alphabetical Listing of Field Variables and Their Definitions
a good heat conductor and a small thermal conductivity with a
poor heat conductor (good insulator). Its unit quantity is thermalconductivity.
Thermal Diff Coef of species-n (in the Species... category) is the thermal
diffusion coefficient for the nth species (DT,i in Equations 7.7-1,
7.7-3, and 7.7-7). Its unit quantity is viscosity.
Time Step (in the Residuals... category) is the local time step of the cell,
∆t, at the current iteration level. Its unit quantity is time.
Time Step Scale (in the Species... category) is the factor by which the
time step is reduced for the stiff chemistry solver (available in the
coupled solver only). The time step is scaled down based on an
eigenvalue and positivity analysis.
Total Energy (in the Temperature... category) is the total energy per unit
mass. Its unit quantity is specific-energy.
Total Energy of phase-n (in the Temperature... category) is the total energy per unit mass of the nth phase. Its unit quantity is specificenergy.
Total Enthalpy (in the Temperature... category) is defined as H + 12 v 2
where H is the Enthalpy and v is the velocity magnitude. Its unit
quantity is specific-energy.
Total Enthalpy of phase-n (in the Temperature... category) is defined as
H + 12 v 2 where H is the Enthalpy of phase-n and v is the phase-n
Velocity Magnitude. Its unit quantity is specific-energy.
Total Enthalpy Deviation (in the Temperature... category) is the difference between Total Enthalpy and the reference enthalpy, H + 12 v 2 −
Href , where Href is the reference enthalpy defined in the Reference
Values panel. The unit quantity for Total Enthalpy Deviation is
specific-energy.
Total Enthalpy Deviation of phase-n (in the Temperature... category) is
the difference between Total Enthalpy of phase-n and the reference
enthalpy, H + 12 v 2 − Href , where Href is the reference enthalpy
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Field Function Definitions
defined in the Reference Values panel. The unit quantity for Total
Enthalpy Deviation of phase-n is specific-energy.
Total Pressure (in the Pressure... category) is the pressure at the thermodynamic state that would exist if the fluid were brought to zero
velocity and zero potential. For compressible flows, the total pressure is computed using isentropic relationships. For constant cp ,
this reduces to:
p0 = p 1 +
γ−1 2
M
2
γ/(γ−1)
(27.4-33)
where p is the static pressure, γ is the ratio of specific heats, and
M is the Mach number. For incompressible flows (constant density
fluid), we use Bernoulli’s equation, p0 = p + pdyn , where pdyn is the
local dynamic pressure. Its unit quantity is pressure.
Total Surface Heat Flux (in the Wall Fluxes... category) is the rate of
total heat transfer through the control surface. It is calculated by
the solver according to the boundary conditions being applied at
that surface. By definition, heat flux out of the domain is negative,
and heat flux into the domain is positive. The unit quantity for
Total Surface Heat Flux is heat-flux.
Total Temperature (in the Temperature... category) is the temperature at
the thermodynamic state that would exist if the fluid were brought
to zero velocity. For compressible flows, the total temperature is
computed from the total enthalpy using the current cp method
(specified in the Materials panel). For incompressible flows, the
total temperature is equal to the static temperature. The unit
quantity for Total Temperature is temperature.
Turbulence... includes quantities related to turbulence. See Chapter 10
for information about the turbulence models available in FLUENT.
Turbulence Intensity (in the Turbulence... category) is the ratio of the
magnitude of the RMS turbulent fluctuations to the reference velocity:
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27.4 Alphabetical Listing of Field Variables and Their Definitions
q
I=
2
3k
vref
(27.4-34)
where k is the turbulence kinetic energy and vref is the reference
velocity specified in the Reference Values panel. The reference value
specified should be the mean velocity magnitude for the flow. Note
that turbulence intensity can be defined in different ways, so you
may want to use a custom field function for its definition. See
Section 27.5 for more information.
Turbulent Dissipation Rate (Epsilon) (in the Turbulence... category) is the
turbulent dissipation rate. Its unit quantity is turbulent-energy-dissrate.
phase-n Turbulent Dissipation Rate (in the Turbulence... category) is the
turbulent dissipation rate for the nth phase. Its unit quantity is
turbulent-energy-diss-rate.
Turbulent Flame Speed (in the Premixed Combustion... category) is the
turbulent flame speed computed by FLUENT using Equation 15.2-4.
Its unit quantity is velocity.
Turbulent Kinetic Energy (k) (in the Turbulence... category) is the turbulence kinetic energy per unit mass defined as
1
k = u0i u0i
2
Its unit quantity is turbulent-kinetic-energy.
(27.4-35)
phase-n Turbulent Kinetic Energy (in the Turbulence... category) is the
turbulence kinetic energy per unit mass (defined above) for the
nth phase. Its unit quantity is turbulent-kinetic-energy.
Turbulent Rate of Reaction-n (in the Reactions... category) is the rate
of progress of the nth reaction computed by Equation 13.1-25 or
13.1-26. For the “eddy-dissipation” model, the value is the same
as the Rate of Reaction-n. For the “finite-rate” model, the value is
zero.
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Field Function Definitions
Turbulent Reynolds Number (Re y) (in the Turbulence... category) is a
nondimensional quantity defined as
√
ρd k
µlam
(27.4-36)
where k is turbulence kinetic energy, d is the distance to the nearest
wall, and µlam is the laminar viscosity.
Turbulent Viscosity (in the Turbulence... category) is the turbulent viscosity of the fluid computed using the turbulence model. Its unit
quantity is viscosity.
phase-n Turbulent Viscosity (in the Turbulence... category) is the turbulent viscosity of the nth phase, computed using the turbulence
model. Its unit quantity is viscosity.
Turbulent Viscosity Ratio (in the Turbulence... category) is the ratio of
turbulent viscosity to the laminar viscosity.
udm-n (in the User Defined Memory... category) is the value of the quantity in the nth user-defined memory location.
Unburnt Fuel Mass Fraction (in the Premixed Combustion... category) is
the mass fraction of unburnt fuel. This function is available only
for non-adiabatic models.
Unsteady Statistics... includes mean and root mean square (RMS) values
of solution variables derived from transient flow calculations.
User Defined Memory... includes quantities that have been allocated to a
user-defined memory location. See the separate UDF Manual for
details about user-defined memory.
User-Defined Scalars... includes quantities related to user-defined scalars.
See the separate UDF Manual for information about using userdefined scalars.
0
UU Reynolds Stress (in the Turbulence... category) is the u 2 stress.
UV Reynolds Stress (in the Turbulence... category) is the u0 v 0 stress.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
UW Reynolds Stress (in the Turbulence... category) is the u0 w0 stress.
Variance of Species (in the NOx... category) is the variance of the mass
fraction of a selected species in the flow field. It is calculated from
Equation 17.1-86.
Variance of Species 1, Variance of Species 2 (in the NOx... category) are
the variances of the mass fractions of the selected species in the
flow field. They are each calculated from Equation 17.1-86.
Variance of Temperature (in the NOx... category) is the variance of the
normalized temperature in the flow field. It is calculated from
Equation 17.1-86.
Velocity... includes the quantities associated with the rate of change in
position with time. The instantaneous velocity of a particle is
defined as the first derivative of the position vector with respect to
time, d~r/dt, termed the velocity vector, ~v .
Velocity Angle (in the Velocity... category) is defined as follows:
For a 2D model,
tan−1
y-velocity-component
x-velocity-component
(27.4-37)
For a 2D or axisymmetric model,
tan
−1
radial-velocity-component
axial-velocity-component
(27.4-38)
For a 3D model,
tan
−1
tangential-velocity-component
axial-velocity-component
(27.4-39)
Its unit quantity is angle.
Velocity Magnitude (in the Velocity... category) is the speed of the fluid.
Its unit quantity is velocity.
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Field Function Definitions
phase-n Velocity Magnitude (in the Velocity... category) is the speed of
the nth phase. Its unit quantity is velocity.
Volume fraction of phase-n (in the Phases... category) is the volume fraction of the nth phase.
Vorticity Magnitude (in the Velocity... category) is the magnitude of the
vorticity vector. Vorticity is a measure of the rotation of a fluid
element as it moves in the flow field, and is defined as the curl of
the velocity vector:
~
ξ = ∇×V
(27.4-40)
VV Reynolds Stress (in the Turbulence... category) is the v 0 2 stress.
VW Reynolds Stress (in the Turbulence... category) is the v 0 w0 stress.
Wall Fluxes... includes quantities related to forces and heat transfer at
wall surfaces.
Wall Shear Stress (in the Wall Fluxes... category) is the force acting tangential to the surface due to friction. Its unit quantity is pressure.
phase-n Wall Shear Stress (in the Wall Fluxes... category) is the force
acting tangential to the surface due to friction on the nth phase.
Its unit quantity is pressure.
Wall Temperature (Inner Surface) (in the Temperature... category) is the
temperature on the inner surface of a wall (corresponding to the
side of the wall surface away from the adjacent fluid or solid cell
zone). Note that wall thermal boundary conditions are applied on
this surface. See also Figure 6.13.2. The unit quantity for Wall
Temperature (Inner Surface) is temperature.
Wall Temperature (Outer Surface) (in the Temperature... category) is the
temperature on the outer surface of a wall (corresponding to the
side of the wall surface toward the adjacent fluid or solid cell zone).
Note that wall thermal boundary conditions are applied on the
Inner Surface. See also Figure 6.13.2. The unit quantity for Wall
Temperature (Outer Surface) is temperature.
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27.4 Alphabetical Listing of Field Variables and Their Definitions
Wall Yplus (in the Turbulence... category) is a nondimensional parameter
defined by the equation
y+ =
ρuτ yP
µ
(27.4-41)
p
where uτ = τw /ρw is the friction velocity, yP is the distance from
point P to the wall, ρ is the fluid density, and µ is the fluid viscosity
at point P . See Section 10.8 for details.
phase-n Wall Yplus (in the Turbulence... category) is the value of y +
computed (as defined above) using the turbulence kinetic energy,
density, and viscosity of the nth phase.
Wall Ystar (in the Turbulence... category) is a nondimensional parameter
defined by the equation
y∗ =
1/4 1/2
ρCµ kP yP
µ
(27.4-42)
where kP is the turbulence kinetic energy at point P , yP is the
distance from point P to the wall, ρ is the fluid density, and µ is
the fluid viscosity at point P . See Section 10.8 for details.
WW Reynolds Stress (in the Turbulence... category) is the w0 2 stress.
X-Coordinate, Y-Coordinate, Z-Coordinate (in the Grid... category) are
the Cartesian coordinates in the x-axis, y-axis, and z-axis directions respectively. The unit quantity for these variables is length.
X Face Area, Y Face Area, Z Face Area (in the Grid... category) are the
components of the boundary face area vectors accumulated to the
boundary cells, for the zones selected in the Boundary Zones list
contained in the Boundary Adaption panel. The face areas are calculated only on the zones selected, and in order to make your selection active, you need to click on the Mark button in the Boundary
Adaption panel. Note that if the Boundary Zones list is empty, all
boundary zones will be used. The face area calculations are done
as in X Surface Area, Y Surface Area, Z Surface Area (see below),
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Field Function Definitions
except the area values in the cells with more than one boundary
face are not summed to obtain the cell values. Instead, the area
value relative to the last visited face of each cell (resulting from
your selection of Boundary Zones) is taken as the cell value.
X Pull Velocity, Y Pull Velocity, Z Pull Velocity (in the Solidification/Melting... category) are the x, y, and z components of the pull velocity
for the solid material in a continuous casting process. The unit
quantity for each is velocity.
X Surface Area, Y Surface Area, Z Surface Area (in the Grid... category)
are the components of the boundary face area vectors accumulated
to the boundary cells. The surface area is accumulated for all
boundary faces. For each boundary face zone, the component of
the face area in the relevant direction (x, y, or z) is accumulated
as the cell value of the adjoining cell. For those cells having more
than one boundary face, the cell value is the sum (accumulation)
of all the face area values. In most circumstances, the X Surface
Area, Y Surface Area, Z Surface Area are used for flux and surface
integration. In the few instances where area accumulation must
be avoided, you can mark the zones of interest and use X Face
Area, Y Face Area, Z Face Area (see above) for flux and integral
calculations.
X Velocity, Y Velocity, Z Velocity (in the Velocity... category) are the components of the velocity vector in the x-axis, y-axis, and z-axis directions, respectively. The unit quantity for these variables is velocity.
phase-n X-Velocity, phase-n Y-Velocity, phase-n Z-Velocity (in the Velocity... category) are the components of the velocity vector in the
x-axis, y-axis, and z-axis directions for each phase. The unit quantity for these variables is velocity.
X-Vorticity, Y-Vorticity, Z-Vorticity (in the Velocity... category) are the x,
y, and z components of the vorticity vector.
X-Wall Shear Stress, Y-Wall Shear Stress, Z-Wall Shear Stress (in the Wall
Fluxes... category) are the x, y, and z components of the force acting tangential to the surface due to friction. The unit quantity for
these variables is pressure.
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27.5 Custom Field Functions
phase-n X-Wall Shear Stress, phase-n Y-Wall Shear Stress, phase-n Z-Wall
Shear Stress (in the Wall Fluxes... category) are the x, y, and z components of the force acting tangential to the surface due to friction
on the nth phase. The unit quantity for these variables is pressure.
27.5
Custom Field Functions
In addition to the basic field variables provided by FLUENT (and described in Section 27.4), you can also define your own field functions to
be used in conjunction with any of the commands that use these variables (contour and vector display, XY plots, etc.). This capability is
available with the Custom Field Function Calculator panel. You can use
the default field variables, previously defined calculator functions, and
calculator operators to create new functions. (Several sample functions
are described in Section 27.5.3.)
Any field functions that you define will be saved in the case file the next
time that you save it. You can also save your custom field functions to
a separate file (as described in Section 27.5.2), so that they can be used
with a different case file.
! Note that all custom field functions are evaluated and stored in SI units.
Any solver-defined flow variables that you use in your field-function definition will be automatically converted if they are not already in SI units,
but you must be careful to enter constants in the appropriate units. Note
also that explicit node values are not available for custom field functions;
all node values for these functions will be computed by averaging the values in the surrounding cells, as described in Section 27.1.2.
27.5.1
Creating a Custom Field Function
To create your own field function, you will use the Custom Field Function
Calculator panel (Figure 27.5.1). This panel allows you to define field
functions based on existing functions, using simple calculator operators.
Any functions that you define will be added to the list of default flow
variables and other field functions provided by the solver.
Define −→Custom Field Functions...
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Field Function Definitions
! Recall that you must enter all constants in the function definition in SI
units.
Figure 27.5.1: The Custom Field Function Calculator Panel
The steps for creating a custom field function are as follows:
1. Use the calculator buttons and the Field Functions list and Select
button to specify the function definition, as described below. (As
you select each item from the Field Functions list or click on a button
in the calculator keypad, its symbol will appear in the Definition
text entry box. You cannot edit the contents of this box directly;
if you want to delete part of a function, use the DEL button on the
keypad.)
2. Specify the name of the function in the New Function Name field.
!
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Be sure that you do not specify a name that is already used for
a standard field function (e.g., velocity-magnitude); you can see
a complete list of the predefined field functions in FLUENT by
selecting the display/contours text command and viewing the
available choices for contours of.
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27.5 Custom Field Functions
3. Click on the Define button.
When you click on Define, the solver will create the function and add it
to the list of Custom Field Functions within the drop-down list of available
field functions. The Define push button is grayed out after you create a
new function or if the Definition text entry box is empty.
Should you decide to rename or delete the function after you have completed the definition, you can do so in the Field Function Definitions panel,
which you can open by clicking on the Manage... push button. See Section 27.5.2 for details.
Using the Calculator Buttons
Your function definition can include many basic calculator operations
(e.g., addition, subtraction, multiplication, square root). When you select a calculator button (by clicking on it), the appropriate symbol will
appear in the Definition text entry box. The meaning of the buttons is
straightforward; they are similar to the buttons you would find on any
standard calculator. You should, however, note the following:
• The CE/C button will clear the entire Definition and the New Function Name, if you have entered one. The DEL button will delete
only the last entry in the Definition text entry box. You can use
DEL to delete characters one at a time, starting with the last one
entered.
• To obtain the inverse trigonometric functions arcsin, arccos, and
arctan, click on the INV button before selecting sin, cos, or tan.
• The ABS button yields the absolute value of the number that follows it, and the log button yields the natural logarithm of the
following number.
• The PI button represents π and the e button represents the base
of the natural logarithm system (which is approximately equal to
2.71828).
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Field Function Definitions
Using the Field Functions List
Your function definition can also include any of the field functions defined
by the solver (and listed in Section 27.4) or by you. To include one of
these variables/functions in your function definition, select it in the Field
Functions drop-down list and then click on the Select button below the
list. The symbol for the selected item will appear in the Definition text
entry box (e.g., p will appear if you select Static Pressure).
27.5.2
Manipulating, Saving, and Loading Custom Field
Functions
Once you have defined your field functions, you can manipulate them
using the Field Function Definitions panel (Figure 27.5.2). You can display
a function definition to be sure that it is correct, delete the function if
you decide that it is incorrect and needs to be redefined, or give the
function a new name. You can also save custom field functions to a file
or read them from a file. The custom field function file allows you to
transfer your custom functions between case files.
To open the Field Function Definitions panel, click on the Manage... button in the Custom Field Function Calculator panel.
The following actions can be performed in the Field Function Definitions
panel:
• To check the definition of a function, select it in the Field Functions
list. Its definition will be displayed in the Definition field. This
display is for informational purposes only; you cannot edit it. If you
want to change a function definition, you must delete the function
and define it again in the Custom Field Function Calculator panel.
• To delete a function, select it in the Field Functions list and click
on the Delete button.
• To rename a function, select it in the Field Functions list, enter a
new name in the Name field, and click on the Rename button.
!
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Be sure that you do not specify a name that is already used for
a standard field function (e.g., velocity-magnitude); you can see
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27.5 Custom Field Functions
Figure 27.5.2: The Field Function Definitions Panel
a complete list of the predefined field functions in FLUENT by
selecting the display/contours text command and viewing the
available choices for contours of.
• To save all of the functions in the Field Functions list to a file, click
on the Save... button and specify the file name in the resulting
Select File dialog box (see Section 2.1.2).
• To read custom field functions from a file that you saved as described above, click on the Load... button and specify the file
name in the resulting Select File dialog box. (Custom field function
files are valid Scheme functions, and can also be loaded with the
File/Read/Scheme... menu item, as described in Section 3.15.)
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Field Function Definitions
27.5.3
Sample Custom Field Functions
When you are checking the results of your simulation, you may find it
useful to define some of the following field functions:
• To define a function that determines the ratio of static pressure to
inlet total pressure, use the relationship
R=
p + pop
pto + pop
(27.5-1)
where p is the static pressure calculated by the solver, pto is the
inlet total pressure, and pop is the operating pressure for the problem. Use the solver-defined function Static Pressure for p, and the
numerical value that you specified for Gauge Total Pressure in the
Pressure Inlet panel for pto . Specify the value of the operating
pressure to be the value that you set in the Operating Conditions
panel. As discussed in Section 7.12, all pressures in FLUENT are
gauge pressures relative to the operating pressure. If the operating pressure is zero, as is generally the case for compressible flow
calculations, the expression for the pressure ratio reduces to
PR =
p
pto
(27.5-2)
• To define a function that determines the critical velocity ratio v/a∗ ,
a parameter that is sometimes used in turbomachinery calculations,
use the relationship
v
=
a∗
1/2
γ+1 (γ−1)/γ
1 − PR
γ−1
(27.5-3)
In this relationship, a∗ is the critical velocity (i.e., the velocity that
would occur for the same stagnation conditions if M = 1), γ is the
ratio of specific heats, and PR is the pressure ratio defined in Equation 27.5-2 for which you created your own function. For γ, ratio
of specific heats, select Specific Heat Ratio (gamma) in the Properties... category. To include PR, select Custom Field Functions... in
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27.5 Custom Field Functions
the first drop-down list under Field Functions, and then select from
the second list the function name that you assigned PR.
• Suppose you have swirling flow in a pipe, aligned with the z axis,
and you want to calculate the flow rate of angular momentum
through a cross-sectional plane:
Z
~
ρrvθ~v · dA
(27.5-4)
You can create a function for the product rvθ , where r is the Radial
Coordinate and vθ is the Tangential Velocity. Then use the Surface
Integrals panel to compute the flow rate of this quantity.
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