
A Multiresolution Vortex Particle-Mesh method for the simulation of incompressible flows
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The Vortex Particle-Mesh (VPM) method, known for its accuracy and its ability to capture the transport of vortical structures over long times and distances, is a state-of-the-art method for simulating vortical flows. It solves the velocity-vorticity form of the Navier-Stokes equations for incompressible flows and combines the advantages of particle methods, i.e., low numerical dissipation and dispersion errors, with those of a mesh-based approach: highly efficient Poisson solvers and finite difference stencils. While it has been proven to be a fast and accurate alternative to pseudospectral solvers and successfully applied across various fields, including wind energy and aircraft wakes, simulations using uniform grids often lead to prohibitive computational costs, particularly in three dimensions. Adaptive Mesh Refinement (AMR) addresses this challenge by dynamically adjusting the local grid resolution based on flow characteristics. However, it introduces additional complexity regarding the algorithm design and (parallel) implementation. The AMR algorithm must efficiently determine where refinement or coarsening is needed while ensuring the conservation properties of the simulated physics. At the same time, the computational overhead associated with grid adaptation must be minimized to preserve the performance gains achieved by reducing the number of unknowns. This work presents a scalable and efficient implementation of the VPM method capitalizing on adaptive grid refinement. Our solver has been developed within murphy[4], a wavelet-based multiresolution framework for scientific computing on 3D block-structured collocated grids. We build a new approach to represent the particles, that allows their refinement or coarsening, thereby facilitating the interpolation between particles and mesh of varying resolutions. To solve the Poisson equation, we employ a Multigrid approach combined with an FFT-based direct solver. The resulting software is designed to leverage massively parallel architectures. It has been leveraged to study the collision of vortex rings at high Reynolds numbers.