4.1 Numerical Aerodynamics
- Wake vortex characterisation of high-lift aircraft (A. Benkenida, G. Jonville,
G. Puigt, D. Darracq)
- Wake vortex dynamics (F. Laporte, H. Moet, D. Darracq)
- Flight Dynamic Coefficients (J. Cormier, S. Champagneux, P. Guillo)
- Turbomachinery Flows (L. Kozuch, R. Struijs, C. Martin, A. Fiala, D. Darracq)
- Propeller aerodynamics (G. Grondin, X. Escrivá, D. Darracq)
- Axial fan optimization (C. Martin, B. Marquez)
- Numerical Simulations of Crosswind Inlet Flows at Low Mach Numbers (S. Champagneux)
4.1.1 Wake vortex characterisation of high-lift aircraft (A. Benkenida, G. Jonville,
G. Puigt, D. Darracq) In the frame of the C-Wake program, inviscid
simulations of the lift-induced wake around full high-lift aircraft
grid systems have been deeply investigated with NSMB. Parametric
studies have also been carried out. It has been demonstrated by CERFACS
that, if the numerical dissipation is carefully controlled, the
wake vortex system could be predicted even in the extented near field
(13 and 6.5 wingspans for, respectively, the NLR-SWIM generic model
[Benkenida, 2001a]
and the DLR-F11 realistic model
[Benkenida, 2001]).
It should be noted that other European
CFD codes involved in C-Wake used by INTA (Spain), CIRA (Italy),
DLR-EA (Germany), BAe Systems (United Kingdom) and CFD-N (Norway) can
only resolve the wake vortices until 1-2 wingspans.
4.1.2 Wake vortex dynamics (F. Laporte, H. Moet, D. Darracq)
Wake vortex instabilities are a promising way of reducing the trailing
edge wake vortex hazard on a following aircraft during approach or
take-off phases at an airport. With the support of the EC (C-Wake,
S-Wake, WakeNet) and of the aeronautical industry (Airbus),
CERFACS has developed a strong expertise on this topic.
By the means of LES, CERFACS has provided numerous analysis of the effect
of the turbulence on a vortex sytem: decay, short-wavelength and
long-wavelength instabilities. CERFACS is investigating this domain by
use of numerical methods through a close collaboration with CNRS-IRPHE
and Airbus France, leading to a patented device. NSMB has been
improved to handle such flows in the following manner:
-
automatic adaptative time step selection based on error
evaluation;
- injection of turbulence by the means of a characteristic
boundary condition;
- extrapolation from numerical/experimental inlet plane.
This activity is still strongly supported by Airbus and EC.
4.1.3 Flight Dynamic Coefficients (J. Cormier, S. Champagneux, P. Guillo)
The CERFACS was involved in this field of research since 1998
[Cormier, 2000].
This work was initialized both by
EADS Missiles and Airbus France for the evaluation of missiles and aircraft
stability. Its results are useful for areas such as flight
dynamics or systems. The final aspects consisted for the largest part
of the validation and the evaluation of the method previously
implemented in the CFD code NSMB for steady configurations
[Cormier, 2000b].
It has been compared to traditionally employed
semi-empirical methods (ESDU) and has permitted to assess the field of
relevancy of each method. The swept-back ONERA M6 wing has been
considered in a wide range of flying conditions
[Guillo, 2000].
Now, the numerical method provided to Airbus France has reached the
level of a design tool within the framework of ``steady'' coefficients
for pitching, rolling and yawing movements. The computation of
``unsteady'' coefficients, which is very close to aeroelastic studies
in terms of numerical ingredients to implement and validate, is the
next
step to be considered.
In the frame of the European Project AWIATOR starting in June 2002,
CERFACS will produce the analysis of the damping derivatives coefficient
of a full aircraft equipped with large winglets by means of RANS
simulations.
4.1.4 Turbomachinery Flows (L. Kozuch, R. Struijs, C. Martin, A. Fiala, D. Darracq)
The NSMB team has started turbomachinery activity at the end of 1998,
in the frame of a regional contract (OCMATH) involving
Liebherr-Aerospace Toulouse (LTS), Technofan and Ratier-Figeac as
industrial partners. Specifically, LTS is interested in the noise
generated by the fans they produce and CERFACS is to perform an unsteady
calculation accounting for inlet distortion. The aerodynamic results
will be used as input for the acoustic code used by LTS. At the
present time, steady computations have been performed using
Baldwin-Lomax turbulence modeling. The turbomachinery use of NSMB has
been validated by comparing both aerodynamic and acoustic results with
those obtained with an industrial turbomachinery code (BToB3D), using
the same mesh. NSMB is also being validated on a turbofan test case,
by comparison with experimental data. With the phase-lag technique, a
major step towards the unsteady simulation has been made by developing
a boundary condition allowing to compute a single blade-to-blade
passage in the case of periodic flow. An inlet distortion has been
simulated
with this technique.
In the frame of the development of the analysis of the acoustics
generated by turbomachines, CERFACS has fulfilled a contract of
collaboration with the laboratory of Ecole Centrale de Lyon.
4.1.5 Propeller aerodynamics (G. Grondin, X. Escrivá, D. Darracq)
Within the frame of the OCMATH region contract, the CFD team has
started propeller activity in 2000. Ratier-Figeac is particurlarly
interested in the prediction of aerodynamics around advanced
high-speed propellers for aeroelastic analysis. CERFACS has developed
parallel meshing techniques aiming at performing steady and unsteady
calculations around rotating
propellers.
At the end 2001, a collaboration started with Airbus France on the
A400M military aircraft project to provide CFD tools for
aerodynamics 1) rotor-stator interaction making use of sliding-mesh
technique, 2) damping derivatives of a propeller modelled by an actuartor
disk.
Figure 4.1: Euler flow simulation around the HSP propeller, M=0.7.
4.1.6 Axial fan optimization (C. Martin, B. Marquez)
In the OCMATH project framework, a set of axial fan computations has
been achieved in order to provide the TECHNOFAN society (SNECMA) with
the most reliable settings of its CFD solver. These settings,
guidelines and results can be consulted respectively in
[Martin, 2000] and [Martin, 2000a].
Through a collaboration
contract with the laboratory of ENSICA, CERFACS is now involved in an
axial fan optimal design process so as to evaluate its efficiency in
the TECHNOFAN fan design process.
Perfect gas computations of high speed flows (S. Champagneux,
B. Marquez, G. Grondin)
The objective was to prove that the CFD code NSMB
possesses the necessary numerical features to compute the flow around
complex 3D geometries in hypersonic flight conditions assuming the gas
to be perfect. The final test case, the flow around a re-entry
capsule called ARD (see Fig.4.2) at a Mach number of 15, has
been successfully computed with the restrictive assumption of dealing
with a perfect gas. Numerical schemes, physical modeling of
turbulence and computational strategies have been widely investigated
to provide EADS Launch Vehicles an efficient way to compute such configurations.
The CFD code NSMB has been delivered to EADS Launch Vehicles and is now used for
various applications.
Figure 4.2: Perfect gas hypersonic viscous flow around the ARD: bow shock and wake.
Real gas computations of high speed flows (Y. Stiriba,
M. Duloué, G. Grondin, D. Darracq)
The NSMB code has also been extended and adapted to
predict flows at chemical and thermal equilibrium using the upwind
AUSM+ scheme in space, and the implicit LU-SGS (Lower-Upper Symmetric
Gauss Seidel) in time. Air was modelled as a mixture of five
species: O, N, NO, O2 and N2, with three chemical
reactions. Thermodynamic properties were computed using Park's model.
Validation of the new code was obtained for hypersonic flows around
two different blunt bodies. Initially, the first order methods
combined with the MUSCL reconstruction have been tested for a 2D
hypersonic viscous flow with M=18 around a cylinder. The second test
was the 3D viscous flow around the ARD reentry vehicle with flight
conditions provided by EADS Launch Vehicles.
4.1.7 Numerical Simulations of Crosswind Inlet Flows at Low Mach Numbers (S. Champagneux)
Work on this topic has been completed this year within the context of
a contract with Airbus
[Champagneux, 2000].
Numerical tools developed during this study have been included in the official
version of the CFD code NSMB. Cross-functionalities have been extended
and verified (implicit, multigrid, central and upwind schemes) leading to
an efficient and precise tool for solving inviscid, laminar and
turbulent flows at all mach numbers with this compressible CFD code.
The final study conducted at CERFACS consisted in the evaluation of the
total pressure distortion that occurs in the fan plane of a nacelle in
crosswind with its engine running when the aircraft is stopped at the
ground just before taking off.
This application has been applied on a generic shape of nacelle.
Now, this tool is used by designers for realistic configurations at Airbus.
Finally, Ralf Heinrich from DLR-EA spent a three month period at CERFACS
to implement this kind of method in the DLR Tau code.
|
|
