Astrophysical Fluid Mechanics: A New Method For Simulating Supersonic Turbulence

Turbulence is worth studying, because of the fundamental role that it plays in astrophysics. Turbulence is frequently modelled by Large Eddy Simulations (LES), where the dynamics of turbulent eddies are computed on large scales, while a subgrid scale model approximates the influence of smaller eddies. In astrophysics the LES approach is challenged, because gravity and thermal processes break the scale-invariance employed in LES over a wide range of scales.

In order to overcome this problem a method called Adaptive Mesh Refinement (AMR) can be used. AMR involves inserting computational grids of higher resolution into turbulent flow regions in which strong shock fronts are forming, and the gas is undergoing a process of gravitational collapse.

However, due to the extreme range of different length scales it is generally impossible to treat fully developed turbulence by means of AMR only. This would require too large a number of refined grids. For this reason, the FEARLESS team has developed a new method that combines AMR with a subgrid scale model that links the notions of AMR and LES.

“FEARLESS stands for Fluid mEchanis with Adaptively Refine Large Eddy SimulationS“, says Wolfram Schmidt, one of the two architects of the FEARLESS project. “This somewhat complicated title captures the major elements of our concept: We intend to carry out simulations of turbulent fluids using a method that adapts dynamically to the simulated flow by refining the computation in those regions in which turbulence is developing“, he explains.

Supercomputing resources are very much required in order to apply this method and the DEISA infrastructure has played an important role in the development of the project.

Results from these simulations are significant for ongoing research into the nature of turbulence in star-forming gas clouds in the Galaxy. The project team expects that FEARLESS will generate new perspectives in astrophysics through the as yet unrivalled levels of sophistication it achieves in the treatment of turbulence.

The FEARLESS project was initiated in 2005 by Jens Niemeyer and Wolfram Schmidt, two astrophysicists from the University of Würzburg in Germany.