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Paper: Wiggle Instability Revisited: The Role of Bulk Viscosity
Volume: 498, Numerical Modeling of Space Plasma Flows ASTRONUM-2014
Page: 203
Authors: Hanawa, T.
Abstract: Wiggle instability, which appears in the numerical models of galactic spiral shocks, is reexamined by taking account of the bulk viscosity. The numerical models hitherto have not taken account of the bulk viscosity explicitly, as far as the author knows. However it provides a dominant term in the pressure tensor in the transition layer of a strong shock, if we take account of a small but finite amount of the viscosity. Although the transition layer is very thin in reality, it is artificially broadened by limited resolution in numerical models. Thus the bulk viscosity should be enhanced according to the resolution to reproduce the pressure tensor properly in the broadened shock transition region. I have made several numerical experiments in order to examine the validity of the argument mentioned above. The enhanced bulk viscosity provides seemingly smooth density and velocity profiles in the transition layer. As a result, the profiles depend little on the angle between numerical cell boundary and the shock front. A stationary plane shock wave is heavily distorted if the wave front is inclined with respect to the cell boundary and the bulk viscosity is not taken into account. Also the odd-even instability is cured by the bulk viscosity. The wiggle instability disappears when the bulk viscosity is enhanced in the regions of converging flow. The enhanced bulk viscosity does not affect the growth of the Kelvin-Helmholtz instability. These results support the above mentioned hypothesis. We also argue the location of the galactic shock on the basis of the wiggle instability free models.
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