Numerical heat conduction in hydrodynamical models of colliding hypersonic flows - Astrophysics > Instrumentation and Methods for AstrophysicsReport as inadecuate




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Abstract: Hydrodynamical models of colliding hypersonic flows are presented whichexplore the dependence of the resulting dynamics and the characteristics of thederived X-ray emission on numerical conduction and viscosity. For the purposeof our investigation we present models of colliding flow with plane-paralleland cylindrical divergence. Numerical conduction causes erroneous heating ofgas across the contact discontinuity which has implications for the rate atwhich the gas cools. We find that the dynamics of the shocked gas and theresulting X-ray emission are strongly dependent on the contrast in the densityand temperature either side of the contact discontinuity, these effects beingstrongest where the postshock gas of one flow behaves quasi-adiabatically whilethe postshock gas of the other flow is strongly radiative. Introducingadditional numerical viscosity into the simulations has the effect of dampingthe growth of instabilities, which in some cases act to increase the volume ofshocked gas and can re-heat gas via sub-shocks as it flows downstream. Theresulting reduction in the surface area between adjacent flows, and thereforeof the amount of numerical conduction, leads to a commensurate reduction inspurious X-ray emission, though the dynamics of the collision are compromised.The simulation resolution also affects the degree of numerical conduction. Afiner resolution better resolves the interfaces of high density and temperaturecontrast and although numerical conduction still exists the volume of affectedgas is considerably reduced. However, since it is not always practical toincrease the resolution, it is imperative that the degree of numericalconduction is understood so that inaccurate interpretations can be avoided.This work has implications for the dynamics and emission from astrophysicalphenomena which involve high Mach number shocks.



Author: E. R. Parkin, J. M. Pittard

Source: https://arxiv.org/







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