by Dr Ralph Sutherland, RSAA, ANU

Fyris Alpha is a high resolution, shock capturing, multi-phase, up-wind Godunov method hydrodynamics code, which includes a variable equation of state, and optional microphysics such as cooling, gravity and mutlitple tracer variables. Fyris Alpha is a successor to earlier generations of hydrodynamics codes which arose from the original work by Collella and Woodward (1984) and earlier pioneering work by van Leer (1979) on high resolution shock capturing hydrodynamics and the PPM algorithm. The Riemann solver used is a new solver, derived from the exact solver of Gottlieb and Groth (1988), which is significantly faster than previous solvers.

The new code (and its framework ZLS) has been designed and developed at RSAA for use primarily in astrophysical applications, such as galactic and interstellar bubbles, hypersonic shocks, and a range of jet phenomena. Fyris Alpha boasts both higher performance and more detailed microphysics than its predecessors, with the aim of producing output that is closer to the observational domain, such as emission line fluxes, and eventually, detailed spectral synthesis.

Fyris Alpha is approximately 75,000 lines of C code (not including third party libraries), and was begun during a study visit to UAO, supported by the Centre for Complex Dynamics, at the Ångström Labotoriet, Uppsala University, Sweden and the code is named after the river that flows through that town (image below).

The code is conceptually made up of an overarching framework, called ZLS, which provides all the standard services needed for any simulation, plus provision for modules of specific algorithm code. Fyris Alpha is the first of these modules, and it encapsulates the split sweep semi-lagrangian remap PPM method used by ppmlr (in turn developed from VH1, Blondin et al. 1998) but with an improved Riemann solver. It also has a number of optimisations that have improved the speed so that additional calculations neeed for multi-phase simulations become practical. Future modules, including magnetohydrodynamics (Fyris Beta) are in development.

Fyris Alpha is being prepared for release to the scientific community. This site will eventually host the code and updates, but in the interim it is being populated with the code description and a suite of verification test models to serve as a reference for early results obtained from the code.

Update, May 2010

The first code paper documenting the hydrodynamic module Fyris Alpha has been accepted, and posted to astro-ph. A release version of the code is now available.

Much of the code was developed with funding from the ARC Discovery Project DP 0664434.

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