Formation of Near-Wall Particle-Streaks
in Particle-Laden Wall-Bounded Turbulent Flows
Luís M. Portela and Valérie Ferrand
Kramers Laboratory
Delft University of Technology, The Netherlands
Lorentz Center Turbulence Workshop
August 21-30, 2006, Leiden, The Netherlands
Motivation
Small
Heavy
P
 1

DP  K
Particle Behavior
Fluid
Particles
Particles
( Young and Hanratty 1991, Pedinotti et al. 1992, Wang and Squires 1996, Rouson and Eaton 2000, Susuki et al. 2000)
Strong accumulation very near the walls
Spatially organized in « streaks » // to the walls
Turbulence Modulation
Particles
Fluid
fluid streaks (Kline et al. 1967)
(two-way coupling)
Strong and non-isotropic attenuation of the turbulence intensity
(Rogers and Eaton 1991, Kulick et al. 1994, Paris and Eaton 1999, Li et al. 2001, Portela and Oliemans 2002)
Dynamics of interaction mechanisms still poorly understood
Objectives of the Study
Particle streaks very near the wall
Gain a better understanding of their formation process
Particle-fluid dynamics
Turbulence structure
Fluid
Particles
Channel Geometry and Flow Parameters
Re  
u H
 500

NP  400 000
P
 8000

DP
1 K
 10 3 
H
4 H
K  2
t K  4
 P 
P
 110
u 2
m  0.16
LX=5H, LY=2H, LZ=H
 
X, Y

Z
64 grid points, periodic BC
48 grid points, refined near the walls
elastic bouncing walls
Eulerian-Lagrangian Simulations
high-resolution LES
point particles approach
Z   4  13

Y   15
X  39
Stokes drag
t   0.24
no gravity
no collisions
Particle Accumulation Very Near the Wall
time evolution of C very near the wall
Z+=2
C
mean concentration profile
<C>
Z+
t1+
t1  7500
t+
60 channel lengths (30H) with bulk velocity

Z
Z+

X
Y+
Spatial Distribution of Particles Very Near the Wall
Z+=2
one-way coupling
u’
Particles move up and down the wall responding to the ejection
and sweep events (Rashidi et al. 1990)

Z
Ejection Sweep Ejection
H

Y
By extension, both « streaky patterns » are also generally attributed to the streamwise vortices
( Pedinotti et al. 1992, Wang and Squires 1996, Rouson and Eaton 2000, Susuki et al. 2000, Marchioli and Soldati 2002)
Spatial Distribution of the Particles Very Near the Wall
particle streaks are
very elongated : ls  LX  2500
associated with a long life time : t s  1000
streamwise vortices
length :
l v  100
“residence time” : t v  10
Formation Process of the Particle Streaks
Formation Process of the Particle Streaks
Determination of the “fully converged” fluid streamlines
fluid-streaks “baselines”
…..
20 LX
Very good correlation with the particle-streaks
Y+
X+
X+
Formation Process of the Particle Streaks
Y+
X+
Time t + t + ; t+ 1000
X+
streamwise vortices cover 6 channel lengths (= 30 H)
Y+
X+
X+
Formation Process of the Particle Streaks
Fixed fluid field + WP=0
t+ 1000
Particles initially uniformly distributed
Y+
X+
X+
Particle streaks formation
=
Slow process of collection due to a local interaction with the fluid streaks
Particle-Streaks Effect on the Near-Wall Turbulence
Relative destruction of the streamwise fluctuations
 u'
rms

2way coupling

<u@P>/<u>

u' rms / u' rms *100
1way coupling
1way coupling
near-wall particles are clearly
associated with low u
 u’<0
%
Z+
Z+=2
Z+
Turbulence attenuation very near the wall not directly
affected by the particle streaks
no
particular
modulation
of u’<0
u’/urms
Particle-Streaks Effect on the Near-Wall Structure
Two-Way Coupling Effect on the Particle Streaks
One-way coupling
Two-way coupling
Y+
X+
X+
Particles streaks are:
<u@P>/<u>
qualitatively equivalent for one-way and twoway coupling cases
fluid-streaks « baselines » not modified
slightly stronger and more defined for the twoway coupling case
more elongated and less wiggly fluid streaks
Z+
Conclusions and Perspective
Particle streaks formation
slow process induced by the local fluid streaks
qualitatively equivalent in one-way and two-way coupling
Particle streaks don’t play a significant role in turbulence modification
Even though the concentration is strong very near the wall, the preferential
concentration there is not a key point in determining turbulence level
Modeling should be focused on particle effect in the buffer layer and log-law layer.

Z

Y