MAESTRO: An Adaptive Low Mach Number Hydrodynamics Algorithm for Stellar Flows

TL;DR

MAESTRO is an advanced low Mach number hydrodynamics code with adaptive mesh refinement, enabling efficient long-time simulations of subsonic stellar flows, including full-star supernova models, by avoiding acoustic wave tracking.

Contribution

This paper extends MAESTRO by integrating adaptive mesh refinement and a novel base state expansion technique for full-star simulations.

Findings

Efficient long-time simulation of subsonic stellar flows.

Accurate modeling of full-star supernova convection.

Demonstrated suitability for Type Ia supernova studies.

Abstract

Many astrophysical phenomena are highly subsonic, requiring specialized numerical methods suitable for long-time integration. In a series of earlier papers we described the development of MAESTRO, a low Mach number stellar hydrodynamics code that can be used to simulate long-time, low-speed flows that would be prohibitively expensive to model using traditional compressible codes. MAESTRO is based on an equation set derived using low Mach number asymptotics; this equation set does not explicitly track acoustic waves and thus allows a significant increase in the time step. MAESTRO is suitable for two- and three-dimensional local atmospheric flows as well as three-dimensional full-star flows. Here, we continue the development of MAESTRO by incorporating adaptive mesh refinement (AMR). The primary difference between MAESTRO and other structured grid AMR approaches for incompressible and low Mach number flows is the presence of the time-dependent base state, whose evolution is coupled to the evolution of the full solution. We also describe how to incorporate the expansion of the base state for full-star flows, which involves a novel mapping technique between the one-dimensional base state and the Cartesian grid, as well as a number of overall improvements to the algorithm. We examine the efficiency and accuracy of our adaptive code, and demonstrate that it is suitable for further study of our initial scientific application, the convective phase of Type Ia supernovae.