Optimal injection condition of a single pulsed vortex generator jet to promote the cross-stream mixing

The flow field of a pulsed vortex generator jet which is injected periodically through a single hole into a boundary layer is described. Measurements of phase-averaged velocity and wall shear stress are made by a hot-wire anemometer and a high response micro-wall flow sensor, respectively. Optimal mixing conditions, based on three parameters, (i) velocity ratio, (ii) duty ratio and (iii) pulse injection frequency, are discussed. The longitudinal vortex structure characteristic of steady injection is obtained at the stable stage of the evolution of the pulsed jet. A peak of the wall shear stress is also observed at the final stage. These mechanisms in the pulsed vortex generator jet enhance the cross-stream mixing to inhibit the boundary layer separation.