Adiabatic Heating of Contracting Turbulent Fluids
  Turbulence influences the behavior of many astrophysical systems, frequently
by providing non-thermal pressure support through random bulk motions. Although
turbulence is commonly studied in systems with constant volume and mean
density, turbulent astrophysical gases often expand or contract under the
influence of pressure or gravity. Here, we examine the behavior of turbulence
in contracting volumes using idealized models of compressed gases. Employing
numerical simulations and an analytical model, we identify a simple mechanism
by which the turbulent motions of contracting gases "adiabatically heat",
experiencing an increase in their random bulk velocities until the largest
eddies in the gas circulate over a "Hubble" time of the contraction. Adiabatic
heating provides a mechanism for sustaining turbulence in gases where no
large-scale driving exists. We describe this mechanism in detail and discuss
some potential applications to turbulence in astrophysical settings.
