Counter-gradient diffusion of Reynolds stress in turbulent Couette flow with forward-facing step

etc15 Tracking Number 114

The turbulent Couette flow with a forward-facing step (sudden contraction) is investigated experimentally and numerically. The particle image velocimetry (PIV) measurement and direct numerical simulation (DNS) prove peculiar turbulence behavior, the counter-gradient diffusion of the Reynolds stress, near the front part of the corner separation on the forward step. The negative turbulence production which follows the counter-gradient diffusion is then evaluated through quadrant analysis. The negative contribution of Q1 and Q3 events inside the shear layer increases with decreasing the Reynolds number. The effect makes the counter-gradient diffusion rather pronounced in lower Reynolds number flows.