Adiabatic Heating of Contracting Turbulent Fluids

TL;DR

This paper investigates how turbulence in contracting astrophysical gases can be sustained through adiabatic heating, where turbulent velocities increase during contraction without external driving, supported by simulations and an analytical model.

Contribution

It introduces a simple mechanism of adiabatic heating of turbulence during contraction, supported by simulations and an analytical framework, expanding understanding of turbulence in astrophysical gases.

Findings

Turbulent velocities increase during contraction due to adiabatic heating.

The largest eddies circulate over a 'Hubble' time of contraction.

Adiabatic heating can sustain turbulence without external energy input.

Abstract

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.