APSARA: A multi-dimensional unsplit fourth-order explicit Eulerian hydrodynamics code for arbitrary curvilinear grids

TL;DR

Apsara is a new fourth-order hydrodynamics code capable of handling arbitrary curvilinear grids, demonstrating high accuracy and superior performance in simulating low-Mach number astrophysical flows and turbulence.

Contribution

The paper introduces Apsara, a novel high-order finite-volume hydrodynamics code for complex grids, with demonstrated accuracy and application to astrophysical turbulence simulations.

Findings

Apsara achieves fourth-order accuracy on smooth grids.

Apsara outperforms PPM in low-Mach number flow simulations.

Successful application to turbulence in supernova core collapse.

Abstract

We present a new fourth-order, finite-volume hydrodynamics code named Apsara. The code employs a high-order, finite-volume method for mapped coordinates with extensions for nonlinear hyperbolic conservation laws. Apsara can handle arbitrary structured curvilinear meshes in three spatial dimensions. The code has successfully passed several hydrodynamic test problems, including the advection of a Gaussian density profile and a nonlinear vortex and the propagation of linear acoustic waves. For these test problems, Apsara produces fourth-order accurate results in case of smooth grid mappings. The order of accuracy is reduced to first-order when using the nonsmooth circular grid mapping. When applying the high-order method to simulations of low-Mach number flows, for example, the Gresho vortex and the Taylor-Green vortex, we discover that Apsara delivers superior results to codes based on the dimensionally split, piecewise parabolic method (PPM) widely used in astrophysics. Hence, Apsara is a suitable tool for simulating highly subsonic flows in astrophysics. In the first astrophysical application, we perform implicit large eddy simulations (ILES) of anisotropic turbulence in the context of core collapse supernova (CCSN) and obtain results similar to those previously reported.