Numerical Simulations of Thermal Instabilities in Stratified Gases

Details Numerical Simulations of Thermal Instabilities in Stratified Gases Numerical Simulations of Thermal Instabilities in Stratified Gases

Dec 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.247..367m&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 247, NO. 3/DEC1, P. 367, 1990

Astronomy and Astrophysics

Astronomy

34

Scientific paper

We present a set of numerical two-dimensional simulations of initially isobaric perturbations in a thermally unstable, optically thin, radiating and gravitationally stratified ionized fluid. Our study was initially motivated by the problem of the nonlinear evolution of isobaric perturbations in typical regions of cooling flows in galaxy clusters, but the results have applicability beyond this particular physical case. We show that buoyancy effects substantially change the nature of the thermal instability, as predicted previously by linear analyses. The final behaviour of the instability, however, does not resemble previous predictions based on either linear theory or more qualitative analysis. For example, we find that a bubble-shaped isobaric perturbation typically undergoes Rayleigh-Taylor and shear flow instabilities, which can disrupt the bubble on a time comparable to the oscillation period about its equilibrium position. Even when completely disrupted, the bubble tends to oscillate about its previous equilibrium position; there is no sign for a continuing monotonic thermal instability. Indeed, the simulations strongly suggest that the perturbation is ultimately dispersed by vortical circulations triggered by the Rayleigh-Taylor and shear flow instabilities. Thus, initially isobaric thermal instabilities do not seem to be an efficient mechanism for removing the gas in the inner region of a cooling flow.

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