Entropy-limited hydrodynamics: a novel approach to relativistic hydrodynamics

TL;DR

Entropy-limited hydrodynamics (ELH) is a new numerical method combining high-order schemes with low-order fluxes driven by entropy measures, offering improved accuracy and efficiency for relativistic hydrodynamics simulations.

Contribution

We introduce ELH, a novel hybrid numerical scheme that enhances relativistic hydrodynamics simulations by combining high-order accuracy with entropy-based flux limiting.

Findings

ELH achieves comparable or better accuracy than traditional methods.

ELH provides up to 50% computational speedup.

ELH performs well in complex astrophysical tests.

Abstract

We present entropy-limited hydrodynamics (ELH): a new approach for the computation of numerical fluxes arising in the discretization of hyperbolic equations in conservation form. ELH is based on the hybridisation of an unfiltered high-order scheme with the first-order Lax-Friedrichs method. The activation of the low-order part of the scheme is driven by a measure of the locally generated entropy inspired by the artificial-viscosity method proposed by Guermond et al. Here, we present ELH in the context of high-order finite-differencing methods and of the equations of general-relativistic hydrodynamics. We study the performance of ELH in a series of classical astrophysical tests in general relativity involving isolated, rotating and nonrotating neutron stars, and including a case of gravitational collapse to black hole. We present a detailed comparison of ELH with the fifth-order monotonicity preserving method MP5, one of the most common high-order schemes currently employed in numerical-relativity simulations. We find that ELH achieves comparable and, in many of the cases studied here, better accuracy than more traditional methods at a fraction of the computational cost (up to 50 % speedup). Given its accuracy and its simplicity of implementation, ELH is a promising framework for the development of new special- and general-relativistic hydrodynamics codes well adapted for massively parallel supercomputers.