Structures of Density Fluctuations at a Low-Mach-Number Turbulent Boundary Layer by DNS

Abstract

We performed a direct numerical simulation of a low-Mach-number turbulent boundary layer using fundamental equations of compressible flow to investigate the relation between vortex structures and the density distribution. A fully developed turbulent boundary layer of compressible flow was reproduced in the simulation. From the turbulence statistics and instantaneous structures of the density fluctuation, we identified different features in the three regions of a near-wall field, far field and flow field outside the turbulent boundary layer. Structures of the density fluctuation could correspond to sound sources in a turbulent boundary layer. We then observed fine-scale structures of the density fluctuation that were strongly related to turbulent vortices in the vicinity of the wall. In addition, there were large-scale density structures in the upper boundary layer. The large-scale structures seem to correlate with the fine-scale structures close to the wall, with there being a non-steady larger-scale density fluctuation profile in the outer region of the boundary layer.