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Wednesday, August 12, 2009
2:30 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Student Seminar

Discontinuous Galerkin methods for compressible gas dynamics in the incompressible limit.

Jeffrey Haack
University of Wisconsin, T-CNLS and CCS-2

Godunov schemes for compressible gas dynamics exhibit difficulties in low Mach number regimes due to the fast time scales of the acoustic waves in the system. However, in the low Mach number (incompressible) limit the compressible equations can be asymptotically approximated by incompressible equations, where these acoustic waves are not important. Godunov schemes cannot ignore these waves, and require much higher resolution in space and time for stability and accuracy purposes than is necessary for the underlying incompressible dynamics.

This work investigates the Discontinuous Galerkin (DG) method in this regime. Rather than tracking the cell averages as in Godunov methods, DG schemes track a finite number of moments of the system in each cell and connect them through finite volume-like flux functions. They are especially attractive because they allow for high orders of accuracy while remaining compact, which allows for easy parallelization. Under the right conditions, numerical experiments with DG methods appear to have eliminated the numerical dissipation problems suffered by Godunov schemes by driving the variables to be continuous at leading order at the cell interfaces, which relaxes the spatial resolution requirements.

In this talk, I will present an asymptotic analysis of the DG method for the incompressible limit of the one-dimensional isentropic Euler equations. The analysis confirms that the method eliminates the need for high spatial resolution, and shows that the limiting method is consistent with the incompressible equations.