An asymptotic-preserving and exactly mass-conservative semi-implicit scheme for weakly compressible flows based on compatible finite elements

TL;DR

This paper introduces a novel semi-implicit finite element scheme for weakly compressible flows that preserves mass exactly, is asymptotic-preserving, and efficiently handles shocks with an artificial viscosity limiter.

Contribution

It develops an asymptotic-preserving, mass-conservative semi-implicit finite element method using compatible spaces and hybridization, suitable for both compressible and incompressible flows.

Findings

Exact pointwise mass conservation achieved.

Method converges to incompressible Navier-Stokes as Mach number approaches zero.

Numerical tests validate stability and accuracy.

Abstract

We present a novel asymptotic-preserving semi-implicit finite element method for weakly compressible and incompressible flows based on compatible finite element spaces. The momentum is sought in an $H(\mathrm{div})$-conforming space, ensuring exact pointwise mass conservation at the discrete level. We use an explicit discontinuous Galerkin-based discretization for the convective terms, while treating the pressure and viscous terms implicitly, so that the CFL condition depends only on the fluid velocity. To handle shocks and damp spurious oscillations in the compressible regime, we incorporate an a posteriori limiter that employs artificial viscosity and is based on a discrete maximum principle. By using hybridization, the final algorithm requires solving only symmetric positive definite linear systems. As the Mach number approaches zero and the density remains constant, the method converges to an $H(\mathrm{div})$-based discretization of the incompressible Navier-Stokes equations in the vorticity-velocity-pressure formulation. Several numerical tests validate the proposed method.