Sound and turbulence modulation by particles in high-speed shear flows

Direct numerical simulations of particle-laden, high-speed shear layers for Mach numbers varying from 0.9 to 2.5 are used to quantify the effect of inertial particles on turbulence and near-field pressure intensity. Particles are seeded within the shear-layer turbulence with an initial mass loading varying between 0 and 10 and Stokes numbers ranging from 1 to 16. Through the shear layer growth, the near-field pressure levels are observed to change by as much as 5 dB compared to unladen flows. In subsonic flow, the sound level increases with particle loading which is consistent with low-Mach number multiphase aeroacoustic theory. This increase, despite a marked decrease in turbulence level, suggests a non-trivial source-to-sound decomposition. Supersonic flows exhibit a different behavior; sound levels decrease with increase particle loading. Additionally, the sub-Kolmogorov-size particles have a broadband effect on the pressure and turbulence spectra: decreasing energy in large-scale components and vice versa for smaller scales. The volume-filtered compressible flow equations are formulated and averaged to obtain a transport equation for the pressure intensity in the presence of particles, which is used to quantify mechanisms of local turbulence-pressure changes.