Direct numerical simulation of stratification effects in a sediment-laden turbulent channel flow

This work presents direct numerical simulations of sediment-laden turbulent channel flows employing an Eulerian-Eulerian approach. The flow is driven by a constant pressure gradient and self-stratifies owing to the presence of settling sediment particles. The study is performed so as to systematically vary the settling velocity of the sediment particles, which is the parameter that controls the stratification of the flow. The effect of stratification is to suppress vertical Reynolds fluxes. For the larger values of settling velocity considered here, the flow relaminarizes below the streamwise velocity maximum, completely suppressing the turbulent vertical mass and momentum transfer. For the cases that remain actively turbulent, Reynolds fluxes are partially suppressed, but remain larger than their viscous counterparts. These cases present a clear pattern of low-speed streaks with a mean separation of approximately 100 wall units. Moreover, for these cases a pattern of high concentration streaks is found to be in high spatial correlation with the low speed streaks.