An Asymptotically-Correct Implicit-Explicit Time Integration Scheme for Finite Volume Radiation-Hydrodynamics

Abstract

Numerical radiation-hydrodynamics (RHD) for non-relativistic flows is a challenging problem because it encompasses processes acting over a very broad range of timescales, and where the relative importance of these processes often varies by orders of magnitude across the computational domain. Here we present a new implicit-explicit (IMEX) method for numerical RHD that has a number of desirable properties that have not previously been combined in a single method. Our scheme is based on moments and allows machine-precision conservation of energy and momentum, making it highly suitable for adaptive mesh refinement applications; it requires no more communication than hydrodynamics and includes no non-local iterative steps, making it highly suitable for massively parallel and GPU-based systems where communication is a bottleneck; and we show that it is asymptotically-accurate in the streaming, static diffusion, and dynamic diffusion limits, including in the so-called asymptotic diffusion regime where the computational grid does not resolve the photon mean free path. We implement our method in the GPU-accelerated RHD code QUOKKA and show that it passes a wide range of numerical tests.

14 pages, 6 figures, submitted to MNRAS; Code available for download at https://github.com/quokka-astro/quokka

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• A novel numerical method for mixed-frame multigroup radiation-hydrodynamics with GPU acceleration implemented in the QUOKKA code
• QED V: Variations in metal loading of galactic winds with element nucleosynthetic origin
• Quokka-based understanding of outflows (QED) -- IV. Limitations of H$\alpha$ as an outflow diagnostic