Development of a Local Immersed Boundary Method on Body-Conformal Grids for the Capture of Geometrical Complex Details in Aerodynamic Simulations

In this paper, we propose an approach based on an Immersed Boundary Method (IBM), to deal with geometrical complex details in CFD simulations. A body-conformal hexahedral mesh describes a simple geometry, while details can be added onto the original geometry using an Immersed Boundary Condition that is local to each detail. The proposed Local Immersed Boundary Method (LIBM) avoids to generate a body-conformal mesh around the details, simplifying mesh generation process and enabling parametric studies on the shape and position of the details. The IBM method consists in forcing the solution through a wall function at some discretization points close to the immersed details. When the background mesh is too coarse in the vicinity of the immersed obstacles, hierarchical mesh adaptation is performed to properly capture the flow physics induced by the presence of the immersed obstacle. The preprocessing is achieved with the Cassiopée pre-/post-processing library and the flow simulation is performed by solving the compressible Reynolds-Averaged Navier-Stokes (RANS) equations with the industrial flow solver CODA. This approach has been validated on three test cases involving different flow topologies in the immersed boundary vicinity: a turbulent flow with an attached boundary layer over a 2D multi-element airfoil, a massively separated flow around a 2D horn-shaped iced-airfoil and a 3D iced-swept wing. The results obtained demonstrate the ability of the LIBM approach to reproduce the fundamental flow features induced by the immersed obstacles. They also highlight the relevance of using this approach as an efficient simulation tool to deal with geometrical complex obstacles, with a significant reduction in mesh generation effort and a good level of solution accuracy during the early stages of the aerodynamic design process.