Steady and Unsteady CFD Analysis of a Half-span Delta Wing
Simone Crippa
Department of Aeronautical and Vehicle Engineering, AVE
Royal Institute of Technology (KTH)
SE-10044, Stockholm, Sweden
[email protected]
The trend to predict the non-linear, unstationary flow-field around modern high-performance
aircrafts poses increasing demands to computational fluid dynamic (CFD) codes. This is the case
both for the development of new codes as well as
for the implementation of new features in existing
codes. Before the use of “non-standard” methods can be applied to the design of new aircrafts,
the improvements have to be validated and their
technology readiness assessed.
codes in their ability to predict the complex physical phenomena that lead to initial shear layer
separation and further progression of the primary
vortex for blunt leading edge delta wings.
The Reynolds number has a higher influence
on the shear layer separation and vortex location
and strength in case of blunt leading edge delta
wings. This may be a constraint to simulate the
flow-field of full-scale aircrafts with modern hybrid RANS and LES methods given the very high
Reynolds numbers and resulting computational
requirements. On the other hand the use of established Reynolds averaged Navier-Stokes (RANS)
methods for predicting the properties of massively
separated, instationary flows is likely to lead to
questionable results.
This is often done by studying simplified geometries that resemble the main flow features
found on the full-scale aircraft.
In case of
high-performance aircrafts, both manned and unmanned, the main flow feature influencing todays
design is the lift-enhancing effect of the vortices
generated by the shear-layer roll-up at the wing
leading edge. In the past, the simplest basic geometry used for these studies has been the flatplate, high-sweep delta wing with sharp leading
edge. This basic geometry has proven to be effective for studying the dominant vortical structures
near the central part of delta wings, such as vortex
breakdown phenomena.
The aim of this study is thus to quantify the
possible improvement of unstationary high-order
simulations such as DES compared to steady or
unsteady RANS simulations using newly developed turbulence models.
The first step is to assess the difference for a
“standard” sharp leading edge case using a 65◦
delta wing for which extensive experimental data
is available ranging mainly from Reynolds numbers of 6 · 106 to 60 · 106 , Mach numbers of 0.4
to 0.9 and AOA of 0◦ to 25◦ . This experimental
data is furthermore of high interest as the same
wind tunnel model features four interchangeable
On the other hand, real applications of delta
wings on aircrafts feature a finite leading edge radius as a compromise has to be found between the
low speed, low angle of attack (AOA) performance
and the high speed, high AOA performance. Thus
a need has emerged to assess and validate CFD
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(a) Wind tunnel model;
AIAA 2004-0765
from J. M. Luckring,
(b) Computational grid
Figure 1: Delta wing configuration
leading edge segments resembling three different
radii and a sharp leading edge. This data has been
collected at NASA’s National Transonic Facility
(NTF) and presents a valuable source mainly in
two aspects; by combining high Reynolds numbers
runs with different leading edge bluntness and
by being an open access database. For further
details see figure 1(a) and e.g., J. M. Luckring,
AIAA 2002-0419.
selected. The reason for this selection is the appearance of the highly instationary vortex breakdown and a lower influence of compressibility effects compared to the other available cases.
The half-body, unstructured grid used in this
study features 7.89 million cells with 16 layers of
prismatic cells in the near-wall region of the delta
wing and sting fitting and a smooth transition to
the tetrahedral grid. See figure 1(b). The numerical grid has been converted from the Cobalt
For this first comparison the Mach 0.4, AOA format to the native Edge format, the “Flexible
◦
23 and Reynolds number 6 · 106 case has been Format Architecture” (FFA) format.
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