The contribution of dilatational motion to energy flux in homogeneous compressible turbulence

We analyse the energy flux in compressible turbulence by generalizing the exact decomposition recently proposed by Johnson (2020 Phys. Rev. Lett. 124, 104501) to study incompressible turbulent flows. This allows us to characterize the effect of dilatational motion on the interscale energy transfer in three-dimensional compressible turbulence. Our analysis reveals that the contribution of dilatational motion to energy transfer is due to three different physical mechanisms: the interaction between dilatation and strain; between dilatation and vorticity; and the self-interaction of dilatational motion across scales. By analysing numerical simulations of freely decaying and forced turbulence, we validate our theoretical derivations and provide a quantitative description of the role of solenoidal and dilatational motions in energy transfer. In particular, we determine the scaling dependence of the dilatational contributions on the turbulent Mach number. Moreover, our findings provide criteria for tuning the parameters in commonly used Smagorinsky and Yoshizawa models for large-eddy simulations of compressible turbulence.