24TH INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES NUMERICAL SIMULATIONS AROUND WING CONTROL SURFACES Guillaume Fillola AIRBUS, Toulouse, Fr Marie-Claire Le Pape Marc Montagnac ONERA, Châtillon, Fr CERFACS, Toulouse, Fr Keywords: Aileron, Spoiler, Chimera Mesh, Patched Grid, Wall Law ABSTRACT ych Adimensioned coordinate y by half span, A study of wing control surface effectiveness =(y-yroot)/b was carried out using numerical simulations chz Local load in z direction with the advanced Reynolds Averaged Navier- Stokes solver elsA. Non-coincident meshing 1 INTRODUCTION techniques were used as to make the mesh generation process more flexible. The first The correct prediction of handling qualities application attempts to predict an aileron and hinge moments induced by the deployment effectiveness using the patched grid meshing of wing control surfaces (spoilers and ailerons) technique combined with a mesh deformation is a crucial point in the general aircraft sizing tool in order to operate the aileron deflection. process with a strong impact on the final aircraft The second one deals with spoiler deployment weight. The complexity of the aerodynamic and involves the Chimera technique, which flows around deployed control surfaces and the allows separating the spoiler meshing from the importance of the flight envelope to be covered wing meshing and so avoiding a complete mesh made difficult the use of CFD in the elaboration re-generation for each spoiler deflection. of Aerodynamic Data. Until now, only very time-consuming and costly wind tunnel tests and not very accurate semi-empirical methods NOMENCLATURE were used. For a long time, CFD has been intensively a Angle of attack used at Airbus for shape design and Sideslip angle b optimization. As configurations are moderately da Aileron deflection angle complex and studies focused on slight ds Spoiler deflection angle geometrical variations, an efficient coincident M0 Free stream mach number structured mesh generation suite has been set up Re Reynolds number around HEXAã mesher. q/E Aero-elastic coefficient (q is the dynamic Thanks to the recent CFD progress in pressure and E the Young’s modulus) meshing techniques, convergence acceleration CL Lift coefficient and calculation performance, more and more CD Drag coefficient numerical simulations are involved in Cl Rolling moment coefficient Aerodynamic Data generation. However, the Cmc Hinge moment coefficient classic coincident structured grid approach does j Twist angle not seem suitable for complex configurations x/c Adimensioned coordinate x by the local such as deployed ailerons and spoilers. chord 1 GUILLAUME FILLOLA Today, the following meshing techniques leads to more upgradeable and inter-operable appear to us as the most promising for control aerodynamic functions, and thus contributes to a surfaces configurations: better integration of different development [1]. · The Patched-Grid technique, which allows Some applications made in Airbus France with meshing independently on each side of the elsA solver are described in [2]. shared boundaries between two blocks, is The main features and numerical functions thus more appropriate to build independent of elsA are listed below: wing section grids. · cell centered code dealing with structured · The Chimera technique is almost the same meshes. technique as the Patched Grid method but is · classical central scheme for Euler model further enriched by the overlapping grid (centered flux with scalar dissipation) capability. Its principle is to mesh · viscous flux computed from cell-centered independently different bodies and then to evaluations of velocity and temperature take into account interactions between the gradients, with possible correction values at different components by interpolations. interfaces. · The Wall Law technique consists in · classical algebraic and transport equations applying the “linear-logarithmic” law on the turbulence models (all of them following first cell, the size of which can be much Boussinesq’s assumption). larger than y+=1. Performance is then · backward-Euler time integration associated improved during calculation without with the LU implicit method. downgrading the solution accuracy. · Wall Law treatment possibility for wall Moreover, it facilitates interpolation issues boundary conditions [3]. for Chimera technique. We describe below the specific techniques This paper first presents a brief summary used in this study for aircraft applications. of the flow solver elsA, as well as the particular techniques to be used. Following is a discussion 2.2 Patched Grid technique around two numerical simulations, with comparison to experimental results. Aileron Complex configurations are decomposed in effectiveness results using the Patched Grid many structured meshes. These blocks are technique will be presented first, followed by connected to each other with shared interfaces spoiler effectiveness results using the Chimera that impose constraints on the grid generation. technique. Indeed, a local mesh refinement in one of the blocks spreads through the entire computational domain with classical coincident structured 2 NUMERICAL METHODS grids. The Patched-Grid technique allows meshing two blocks independently on each side 2.1 elsA solver of their shared boundaries. A local mesh With the objective of federating all refinement has then a lesser impact on the other national research teams and taking advantage of blocks. Thus the computer memory required and older functionalities implemented in separate CPU time are reduced since the number of grid CFD codes, ONERA has been developing a new points decreases. generation solver called elsA since 1996, in co- The most important characteristic of this operation with CERFACS since 2000. It has technique is to provide the conservation been designed according to an Object Oriented property of the numerical scheme as shown in design method and it is mainly coded with C++ [4] and [5]. This paper uses the approach language, even though the most CPU-expensive described in [6]. Further details, complements loops are coded with Fortran language for better or other methods related to this technique can be numerical efficiency. This innovative approach found for example in [7], [8], [9] and [10]. 2 NUMERICAL SIMULATION AROUND WING CONTROL SURFACES A bi-dimensional overview of the patched operations are applied on each block grid technique is shown in Figure 1. 1 2 independently and hence FAM = F for planar AM Block 1 Block 2 border surfaces. If the border surface is curved, then this technique is said quasi-conservative 1 2 since FAM and FAM might slightly differ according to the point projection process. The ghost cells are filled thanks to an a- weighted interpolation process of the state vector in order to keep the efficiency of implicit time-integration algorithms. 2.3 Chimera technique The Chimera method is based on an overset grid technique [12]. The principle is to generate independent meshes around different body elements, and to solve the global flow by Figure 1 : Two blocks with a shared patched using interpolation technique in the CFD solver. grid interface. More precisely, on the one hand the mesh areas overlapped by bodies are not computed by the solver and body influence comes from a cell The indices (i,j) refer to the location of crown around each body; on the other hand, cells in both blocks and the border surface is domain influence goes through outflow located at the index ½. For comprehensive boundaries. This technique allows almost purposes, it is assumed that the border surface is independ body meshing; meshes must only plane that is to say there is neither overlapping sufficiently overlap to allow interpolations. As nor gaps between cells that are next to the for the independent bodies, refined meshes surface border. The principle of the patched grid make this constraint respected. However, when is explained with the example of the cell (i1,j1) bodies are next to each other and because of of block 1. The numerical flux through the blanking, areas near junctions are not interface AB can be written: discretized. In order to by-pass this difficulty, the solution - used in the present work - is to 1 1 1 generate a mesh leaning on the body of the other F = F = aF (W ,W ) + AB 1 / 2 , j1 AM i1, j1 i2, j2 mesh. 1 (1) (1-a)FBM (Wi1, j1,Wi2, j2+1) In the elsA software, the interpolation is piecewise linear by tetrahedron, each cell being AM divided into 24 tetrahedrons. Bodies are with a = and W represents the AB modeled by a great number of parallelepipeds. Interpolation cell search becomes efficient by conservative state vector or any other fields and using a preconditioned Cartesian grid and other a is the intersection area computed from the two acceleration techniques to find the interpolation border interfaces of the cells (i1,j1) and (i2,j2). tetrahedron [13]. In order to reduce overlapping The intersection surface of these two interfaces constraints and to avoid some points from is obtained with the intersection polygon given becoming orphan, extrapolation from by a Sutherland-Hodgman polygon-clipping neighbouring cells is allowed; the numerical algorithm [11]. scheme is also degenerated on overlapping This treatment of spatial fluxes enables to boundaries and around bodies, thus maintain the global conservation along the patched grid border surface. Indeed, the above 3 GUILLAUME FILLOLA interpolation crown and boundaries have a grid around the wing completed by a pivot on width of one cell