A stable and explicit fluid–structure interaction solver based on lattice-Boltzmann and immersed boundary methods

Fluid–structure interaction (FSI) occurs in a wide range of contexts, from aeronautics to biological systems. To numerically address this challenging type of problem, various methods have been proposed, particularly using implicit coupling when the fluid and the solid have the same density, i.e., the density ratio is equal to 1. Aiming for a computationally efficient approach capable of handling strongly coupled dynamics and/or realistic conditions, we present an alternative to the implicit formulation by employing a fully explicit algorithm. The Lattice Boltzmann Method (LBM) is used for the fluid, with the finite element method (FEM) utilized for the structure. The Immersed Boundary Method (IBM) is applied to simulate moving and deforming boundaries immersed in fluid flows. The novelty of this work lies in the combination of Laplacian smoothing at the fluid/solid interface, an improved collision model for the LBM, and a reduction of non-physical frequencies on the structure mesh. The use of these adaptations results in a solver with remarkable stability properties, a primary concern when dealing with explicit coupling. We validate the numerical framework on several challenging test cases of increasing complexity, including 2D and 3D configurations, density ratio of 1, and turbulent conditions.