A novel numerical method for mixed-frame multigroup radiation-hydrodynamics with GPU acceleration implemented in the QUOKKA code

Abstract

Mixed-frame formulations of radiation-hydrodynamics (RHD), where the radiation quantities are computed in an inertial frame but matter quantities are in a comoving frame, are advantageous because they admit algorithms that conserve energy and momentum to machine precision and combine more naturally with adaptive mesh techniques, since unlike pure comoving-frame methods they do not face the problem that radiation quantities must change frame every time a cell is refined or coarsened. However, implementing multigroup RHD in a mixed-frame formulation presents challenges due to the complexity of handling frequency-dependent interactions and the Doppler shift of radiation boundaries. In this paper, we introduce a novel method for multigroup RHD that integrates a mixed-frame formulation with a piecewise powerlaw approximation for frequency dependence within groups. This approach ensures the exact conservation of total energy and momentum while effectively managing the Lorentz transformation of group boundaries and evaluation of group-averaged opacities. Our method takes advantage of the locality of matter-radiation coupling, allowing the source term for $N_g$ frequency groups to be handled with simple equations with a sparse Jacobian matrix of size $N_g+1$, which can be inverted with $O(N_g)$ complexity. This results in a computational complexity that scales linearly with $N_g$ and requires no more communication than a pure hydrodynamics update, making it highly efficient for massively parallel and GPU-based systems. We implement our method in the GPU-accelerated RHD code QUOKKA and demonstrate that it passes a wide range of numerical tests, including preserving the asymptotic diffusion limit. We demonstrate that the piecewise powerlaw method shows significant advantages over traditional opacity averaging methods for handling rapidly variable opacities with modest frequency resolution.

18 pages, 8 figures, MNRAS in press. The code described in this article is available at: https://github.com/quokka-astro/quokka

References in corpus (13)

• Fornax: a Flexible Code for Multiphysics Astrophysical Simulations
• Equations and Algorithms for Mixed Frame Flux-Limited Diffusion Radiation Hydrodynamics
• An Unstable Truth: How Massive Stars get their Mass
• Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities
• A numerical model for multigroup radiation hydrodynamics
• CASTRO: A New Compressible Astrophysical Solver. III. Multigroup Radiation Hydrodynamics
• A New Algorithm for 2-D Transport for Astrophysical Simulations: I. General Formulation and Tests for the 1-D Spherical Case
• Outflows Driven by Direct and Reprocessed Radiation Pressure in Massive Star Clusters
• Quokka: A code for two-moment AMR radiation hydrodynamics on GPUs
• A multigroup diffusion solver using pseudo transient continuation for a radiation-hydrodynamic code with patch-based AMR
• The influence of frequency-dependent radiative transfer on the structures of radiative shocks
• An Asymptotically-Correct Implicit-Explicit Time Integration Scheme for Finite Volume Radiation-Hydrodynamics
• An accurate treatment of scattering and diffusion in piecewise power-law models for cosmic ray and radiation/neutrino transport

Cited by in corpus (1)

• Multigroup Radiation Diffusion on a Moving Mesh: Implementation in RICH and Application to Tidal Disruption Events