LES and Wall Model LES for aerodynamic flows on curved boundaries in Lattice Boltzmann Method

Abstract

The aim of this thesis project is to solve the flow field characterizing aerospace bodies in an incompressible context with relatively low Reynolds numbers. It is the result of approximately four months of collaboration with the German Aerospace Center (DLR) located in Dresden, which allowed us to leverage the computational power of the HPC CARA. The project was conducted within a non-conventional framework that is continuously evolving, namely the Lattice Boltzmann Method. In this context, particular attention was given to using methods that follow the standard Large Eddy Simulations logic and the introduction of a Wall Model to more accurately characterize the boundary layer, modeling turbulence scales near solid walls. Since the LBM solver used, namely Musubi, operates on Cartesian grids, the solid body, even with its curvature, will always be represented with a staircase approximation. However, special emphasis was placed on researching a way to internally communicate the real geometry of the body to the code in order to adapt the boundary conditions accordingly. To achieve this primary goal, we first focused on simpler problems and, as we obtained correct results, we could advance and complicate the study. The objective of this work is to establish a solid foundation of results obtained through standard DNS and LES for use as a reference to validate those obtained with the new method and, in the future, to do the same with significantly higher Reynolds numbers. We have seen how to proceed to compute DNS and LES within the LBM framework before implementing the Wall Model. Finally, the new method was applied to an infinite 3D wing and a cylinder, showing promising results regarding the evaluation of the velocity field. However, the same method exhibited clear weaknesses in attempting to reconstruct the pressure field, making it impossible to achieve one of the primary goals of CFD, which is the assessment of the forces acting on the body.