Lattice Boltzmann DNS of decaying compressible isotropic turbulence with temperature fluctuations

Abstract

Direct numerical simulation (DNS) of low Mach number decaying isotropic turbulence with randomly distributed initial temperature field is performed using the hybrid thermal lattice Boltzmann method (HTLBM). The objective of the study is to investigate the effect of temperature fluctuations on turbulence: specifically, the interaction between kinetic and thermal energy modes and the small-scale flow structure. The results indicate that pressure plays a crucial role in the energy exchange between kinetic and thermal modes. Unlike dissipation, which generates one-way energy transfer from kinetic to thermal modes, pressure can lead to a two-way energy transfer. On average, pressure work transfers energy from thermal to kinetic modes in our computations. The analysis of velocity-gradient structure shows that, as in isothermal flow, the vorticity vector aligns with the intermediate eigenvector of the strain-rate tensor. However, the alignments among vorticity vector, pressure gradient, density gradient and temperature gradient are significantly altered by temperature fluctuations. Our results demonstrate that HTLBM is a reliable tool for low Mach number turbulent flows with temperature fluctuations.