High order treatment of moving curved boundaries: Arbitrary-Lagrangian-Eulerian methods with a shifted boundary polynomials correction

In this paper we present a novel approach for the prescription of high order boundary conditions when approximating the solution of the Euler equations for compressible gas dynamics on curved moving domains. When dealing with curved boundaries, the consistency of boundary conditions is a real challenge, and it becomes even more challenging in the context of moving domains discretized with high order Arbitrary-Lagrangian-Eulerian (ALE) schemes. The ALE formulation is particularly well-suited for handling moving and deforming domains, thus allowing for the simulation of complex fluid-structure interaction problems. However, if not properly treated, the imposition of boundary conditions can lead to significant errors in the numerical solution, which can spoil the high order discretization of the underlying mathematical model. In order to tackle this issue, we propose a new method based on the recently developed shifted boundary polynomial correction, which was originally proposed on fixed meshes. The new method is integrated into the space-time corrector step of a direct ALE finite volume method to account for the local curvature of the moving boundary by only exploiting the high order reconstruction polynomial of the finite volume control volume. It relies on a correction based on the extrapolated value of the cell polynomial evaluated at the true geometry, thus not requiring the explicit evaluation of high order Taylor series. This greatly simplifies the treatment of moving curved boundaries, as it allows for the use of standard simplicial meshes, which are much easier to generate and move than curvilinear ones, especially for 3D time-dependent problems. Several numerical experiments are presented demonstrating the high order convergence properties of the new method in the context of compressible flows in moving curved domains, which remain approximated by piecewise linear elements.