Forced turbulence in thermally bistable gas: A parameter study
  Context: The thermal instability is one of the dynamical agents for
turbulence in the diffuse interstellar medium, where both, turbulence and
thermal instability interact in a highly non-linear manner. Aims: We study
basic properties of turbulence in thermally bistable gas for variable
simulation parameters. The resulting cold gas fractions can be applied as
parameterisation in simulations on galactic scales. Methods: Turbulent flow is
induced on large scales by means of compressive stochastic forcing in a
periodic box. The compressible Euler equations with constant UV heating and a
parameterised cooling function are solved on uniform grids. We investigate
several values of the mean density of the gas and different magnitudes of the
forcing. For comparison with other numerical studies, solenoidal forcing is
applied as well. Results: After a transient phase, we observe that a state of
statistically stationary turbulence is approached. Compressive forcing
generally produces a two-phase medium, with a decreasing fraction of cold gas
for increasing forcing strength. This behaviour can be explained on the basis
of turbulent mixing. We also find indications for power-law tails of
probability density functions of the gas density. Solenoidal forcing, on the
other hand, appears to prevent the evolution into a two-phase-medium for
certain parameter regions. Conclusions: The dynamics of thermally bistable
turbulence shows a substantial sensitivity on the initial state and the forcing
properties.
