Sensitivity of an asymmetric, three-dimensional diffuser to inlet condition perturbations

The sensitivity of a three-dimensional, asymmetric diffuser to inlet condition perturbations was investigated using dielectric barrier discharge plasma actuators. Previous experimental and computational studies revealed the sensitivity of the separated flow in this diffuser to secondary flows in the inlet duct of the diffuser. By purposefully altering these secondary flows with highly tunable plasma actuators, the diffuser's pressure recovery could be both significantly improved and degraded. Two cases, one with pulsed forcing and another with continuous forcing, were selected for further study using 2D particle image velocimetry (PIV). PIV data were acquired in five streamwise-wall-normal planes. These measurements reveal that the relatively weak spanwise forcing introduced by the plasma actuators changes the size and orientation of the separation bubble. Pulsed forcing produces a strong peak in the Reynolds shear stress in the boundary layer upstream of separation. This significantly delays separation leading to a large increase in diffuser pressure recovery. In contrast, continuous plasma actuator forcing causes early separation on the diffuser sidewall, completely changing the separation geometry. This causes a larger and more unsteady separation bubble with higher reversed flow velocities which contribute to losses in the diffuser's pressure recovery.