A DSMC view of the problem of bulk viscosity in thermal nonequilibrium

Spontaneous fluctuation power spectra in the hydrodynamic regime are obtained from DSMC simulations of a model gas with internal degrees of freedom. The simulated spectra are compared with the theoretical results derived from one-temperature and two-temperature hydrodynamic conservation equations. The comparison allows to establish the limitations of a bulk viscosity description of the internal energy relaxation kinetics.