Control of Turbulent Separation by Periodic Suction and Injection

Effects of periodic perturbation on the turbulent separating flows in a plane two-dimensional asymmetric diffuser have been experimentally investigated. The perturbation was accomplished by alternating injection and suction through a two-dimensional slit located upstream of the expected detachment point. The results indicate that the pressure recovery along the diffuser depends on the frequency as well as the amplitude of the injection/suction flow ; the maximum improvement was achieved at St∼0.03, the Strouhal number St being based on the channel width and channel center velocity at the inlet of the diffuser. The phase-averaged velocity distributions at each phase of the oscillation were evaluated by means of synchronized sampling of the velocity signal employing direction-sensible hot-wire anemometry. A wavy pattern of the instantaneous streamlines, obtained from the velocity profiles, extends throughout the entire region of the diffuser, confirming an enhanced momentum transport due to the organized oscillatory fluid motion.