Amine Ben Haj Ali

An accurate positivity preserving scheme for the spalart-allmaras turbulence model. application to aerodynamics

We propose an accurate numerical method preserving the positivity of the turbulent viscosity in the Spalart-Allmaras model focusing in particular on the stiffness of the source term. The goal is to apply this model for turbulent flows using an effective numerical method based on a mixed FEFV method. A mathematical analysis of the continuous and numerical model are provided. Three-dimensional numerical simulations of turbulent flows on wings using unstructured grids will be presented.

Robust moving-mesh algorithms for hybrid stretched meshes : application to moving boundaries problems

A robust Mesh-Mover Algorithm (MMA) approach is designed to adapt meshes of moving boundaries problems. A new methodology is developed from the best combination of wellknown algorithms in order to preserve the quality of initial meshes. In most situations, known MMAs distribute mesh deformation while preserving a good mesh quality. However, invalid meshes are generated when the motion is complex and/or involves multiple bodies. After studying few MMAs limitations, we propose the following approach: use the Inverse Distance Weighting (IDW) function to produce the displacements field, then the Geometric Element Transformation Method (GETMe) smoothing algorithms to improve the resulting mesh quality and use an untangler to revert negative elements. The proposed approach has been proven efficient to adapt meshes for various realistic aerodynamic motions: a symmetric wing has suffered large tip bending and twisting and the high-lift components of two wings (one rectangular and one swept) have moved to different flight stages. Finally, the fluid flow has been solved on adapted meshes and their results are close to experimental ones. However, for situations where moving boundaries are close to contact more improvements need to be made or other approaches should be considered such as the overset grid method.