Annual Report


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4.1   Numerical Aerodynamics

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:
  1. automatic adaptative time step selection based on error evaluation;
  2. injection of turbulence by the means of a characteristic boundary condition;
  3. 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.

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