Active Flow Control of Separation in a Branched Duct

Regulation of flow diversion from a primary rectangular channel into a branched secondary duct having an inlet section that spans one of the channel walls is investigated experimentally (Mo ≤ 0.4) using active flow control. The flow distribution between ducts is effected by controlling the inherent separation at the upstream edge of the compact secondary duct inlet using an integrated spanwise array of fluidic oscillating jets. The primary and secondary flows are characterized in the absence and presence of actuation using surface pressure distributions, Mach number mapping, and particle image velocimetry. It is shown that the fluidic actuation can regulate the increase in diverted mass flow rate by more than 50%. Furthermore, the mass flow rate through the primary channel increases by up to 25% due to associated reduction in losses at the entrance to the secondary duct. Analysis of the flow field in the vicinity of the separation using proper orthogonal decomposition (POD) indicates that the actuation significantly alters its incipient dynamics. As the magnitude of the actuation increases, the energy content of the dominant POD modes near separation is enhanced as manifested by the increase in the characteristic scale of the vorticity concentrations. These changes suggest that the present actuation is dissipative and therefore limits fine-scale dynamics.