DNS of particle-laden flow over a backward facing step at a moderate Reynolds number

The present study investigates turbulence modification by particles in a backward-facing step flow with fully developed channel flow at the inlet. This flow configuration provides a range of flow regimes, such as wall turbulence, free shear layer and separation, in which to compare turbulence modification. Fluid-phase velocities in the presence of different mass loadings of particles with a Stokes number of St = 3.0 are studied. Local enhancement and attenuation of the streamwise component of the fluid turbulence of up to 27% is observed in the channel extension region for a mass loading of phi = 0.2. The amount of modification decreases with decreasing mass loading. No modification of the turbulence is found in the separated shear layer or in the re-development region behind the re-attachment, although there were significant particle loadings in these regions.