Accurate and fast simulation-based processes are key to the design of future aircraft. Computational Fluid Dynamic technology at Dassault Aviation relies on numerical formulations developed by T.J.R. Hughes. Continued efforts over the past years have led to impressive capability and new tools that are applied to the design of both long-range business jets and military aircraft. Recent advances are related to multidisciplinary design technology and to complex flow physics associated to turbulence and transition phenomena. This paper will present a number of examples to illustrate these new capabilities. Methods developed for the flutter analysis of configurations with complex flow features will be discussed. Aerodynamic simulations required for structural fatigue analysis will also be presented. Finally, complex thermodynamics capabilities will be illustrated.

Three Reynolds-Stress Models (RSMs) have been benchmarked on industrial configurations with aeronautical applications. The models are first compared on a zero-pressure-gradient boundary layer, which highlights the differences in the near-wall approaches of the models. Results are then analyzed for the Skare & Krogstad adverse-pressure-gradient boundary layer and the Common Research Model (CRM) aircraft for two Reynolds numbers. Both cases display improvements in using RSMs over the eddy-viscosity Spalart-Allmaras model. Two of the considered second-moment closures better predict the boundary layer growth and its shape factor in the Skare & Krogstad test case, and all noticeably improve the drag-due-to-lift in the CRM case.

A new version of the Spalart-Allmaras model is presented to improve adverse pressure gradient flow predictions. High fidelity numerical simulations confirmed the sensitivity of the log-law region to the pressure gradient, for both its slope and its intercept. The study is limited to the correction of the slope by tuning the von Karman constant according to the local dimensionless pressure gradient p+ and is a first step towards better approach to account for pressure gradients. A new model is calibrated on a NACA 4412 wing at Rec = 1M section and then applied to 3D cases, including a simplified aircraft configuration. The new model displays encouraging results regarding the inner layer but exhibits limitations in the outer layer and the need for another kind of correction.

To create efficient new aerodynamic designs or predict the onset of flutter, the linearised Navier-Stokes equations might be used. In some cases, many right-hand sides must be solved keeping the same matrix. In this paper, techniques which enable to solve several righthand sides at the same time, such as Block GMRes, or reuse pieces of information computed in the previous solves, such as Krylov space recycling, are investigated. They will be tested on both simple and industrial test cases.

This chapter describes the contribution of Dassault Aviation to the IDIHOM Project. It focuses on the extension of its stabilized finite element Navier-Stokes code to higher-order elements and more specifically on industrial RANS and DES applications.

The purpose of the present paper is to assess the predictive capability of Reynolds-averaged Navier-Stokes computations using seven-equation Reynolds-stress model wall-normal-free closures for flows in aircraft-engine intake double-S-duct configurations. The intake studied operates at high subsonic Mach numbers and is characterized by high turning angle of the second S-leg, inducing a particularly complex flow structure up to the engine face. Computations were run using two wall-topology-free second-moment closures and a baseline two-equation model, carefully checked for grid convergence, and compared with available experimental measurements. Computational data were then used to analyze the flowfield structure.

Efficient and reliable simulation-based processes are essential to the design of innovative and competitive future aircraft. Continued efforts over the past years have lead to impressive progress and new tools. The review presentation will illustrate key issues associated to the following topics: automatic shape optimization, aerodynamic models for aeroelastic analysis, Detached Eddy Simulation (DES) for complex flows and loads, aeroacoustics and uncertainty quantification.

The purpose of the present paper is the assessment of wall-topology free second-moment and k closures for the computation of flows in aircraft engine intake U-duct configurations. It is shown that the wall-normal-free Reynolds-stress model with an optimized redistribution-term closure is in good agreement with experiment, largely improving upon linear 2-equation closure.

The control of cavity flows has been investigated by the means of Large Eddy Simulations. The computations have been carried out on unstructured meshes to assess the efficiency of two passive acoustic oscillation suppression devices: the rod-in-crossflow and the flat-top spoiler. Despite a sustained interest and many experiments, a clear explanation for observed reduction in the flow-induced structure load is still missing. This work explores different hypotheses: the modification of the mean field and its linear stability properties, a pure deflection effect of the separated shear layer, or scale coupling between the rod wake and the turbulent mixing layer over the cavity. The aim here is to enhance the experimental database and provide leads towards a better understanding of the phenomena. The selected test-case is a cavity of length/depth ratio equal to 5, at Mach and Reynolds number of M∞=0.85 and ReL=7.106, respectively.

The paper first describes developments performed to achieve an accurate and efficient simulation capacity using turbulence models based on the LES and DES approaches. The development is performed within the industrial code used at Dassault for the aerodynamics design of both military aircraft and business jets. The issues of subgrid scale implementation and wall treatment approaches are addressed. The paper then presents industrial applications performed at Dassault related to aerodynamic design. Examples demonstrate the impact of LES and DES on key design issues where complex flow features are present.

We present subgrid closures for large-eddy Simulation (LES) likely to be implemented in stabilized finite element methods. Selection criterion, dynamic procedure and multiscale approach are compared within simulations of freely decaying isotropic turbulence. In all cases, the numerical dissipation coming from the least-squares stabilization dominates the subgrid model. Despite this large numerical dissipation, the LES model, whichever it is, provides a sufficient physical dissipation to have a clear and major effect on the results. In particular the dynamic procedures and the multiscale models turn out to be very efficient, high-lighting a self-adaptive behaviour of the turbulent viscosity and consequently predict the correct energy transfer mechanisms, by accounting for the numerical part of the total dissipation.

Since CFD is crucial for an accurate aerodynamic design of aircraft, Dassault Aviation was involved in many of the major European projects dedicated to the improvements of CFD technologies, such as EUROVAL, ECARP, AVTAC, LESFOIL, UNSI, IDeMAS. The ambitious goals of Flomania, together with the expertise of the partners involved, naturally motivated us to take an active part into the project.

The paper's leitmotiv is condensed in one word: robustness. This is a real hindrance for the successful implementation of any multigrid scheme for solving the Navier–Stokes set of equations. In this paper, many hints are given to improve this issue. Instead of looking for the best possible speed‐up rate for a particular set of problems, at a given regime and in a given condition, the authors propose some ideas pursuing reasonable speed‐up rates in any situation. In a previous paper, the authors presented a multigrid method for solving the incompressible turbulent RANS equations, with particular care in the robustness and flexibility of the solution scheme. Here, these concepts are further developed and extended to compressible laminar and turbulent flows. This goal is achieved by introducing a non‐linear multigrid scheme for compressible laminar (NS equations) and turbulent flow (RANS equations), taking benefit of a convenient master–slave implementation strategy. Copyright © 2004 John Wiley & Sons, Ltd.

The state of the art of Computational Fluid Dynamics and the axis of improvements are described. The issue of flutter prediction is addressed first: the use of linearized Euler solvers for transonic flutter is explained. Recent advances in optimum aerodynamic shape design are presented next, the results demonstrate the applicability of optimization based on the Euler equations and open the way to multidisciplinary optimum design. Finally, the use of Large Eddy Simulation for accurate turbulent flow simulation is illustrated.

A methodology for convergence speed-up of a fully implicit solver for the Ran- dom Averaged Navier-Stokes (RANS) equations for incompressible flows using multigrid (MG) techniques is here presented. The RANS set, comprising the mean flow Navier- Stokes equations and a 2-equation k- turbulence model, is discretized in space by applying the finite element method onto a hierarchy of meshes of dierent element sizes. To solve the system in the finest discretization, a non-linear multigrid scheme is applied to the hi- erarchy. A second objective of this work is to make more robust multigrids, trying to keep good speed-up rates. Considering this paper as a first part of a larger work, we leave aside momentarily the quest for the best possible speed-up rates, to develop some ideas that can make our multigrid more reliable, less dependent to the kind of problem we deal with or to the way the grid hierarchies are constructed: no particular grid-coarsening strategy is studied here. Among these ideas are a new residual transfer operator, boundary conditions treatment and dierent ways of implementing cascadic start-ups. This last point is very

This paper describes the implementation of a finite-element Navier-Stokes code on two parallel architectures: the IBM SP2 and the NEC SX-4. although these implementations are based on two different memory representations, the shared-and the distributed-memory paradigms, the actual source codes are extremely similar, thanks to the finite-element structure of the program. Two industrial applications exemplify the use of parallel computers in the Aerodynamic Modelization Department at Dassault Aviation.

Novel approaches are investigated to solve the unsteady N.S. equations. They are based on a POD method and extend previous work to compressible Navier-Stokes equations and a solution where space discretisation is based on unstructured meshes. The numerical approach developed here is described along with choices related to efficient implementation. The problem of numerical stability is discussed and the use of assimilation techniques is explored. The proposed methods are tested for the unsteady periodic flow over a NACA0012 airfoil.