The transient process of flow separation and reattachment to a concave surface was investigated experimentally on the rear ramp of a modified Glauert Laminar Airfoil Section II, The measurements were carried out at low incompressible speeds using miniature time-resolved piezoresistive pressure transducers (Endevco model). These measurements were supplemented by flow visualization and by exploratory use of a particle image velocimeter. It was observed that the concavity of the surface impeded flow reattachment, and therefore a much higher momentum coefficient was required to partially attach the flow to a concave surface than to a straight one when both surfaces were supposed to turn the flow by the same amount. Streamwise vortices were observed to exist on the concave ramp of the modified Glauert Laminar Airfoil Section II, and thus the interaction of streamwise and span wise vortices and their impact on flow control are discussed. Lift augmentation by periodic excitation is mainly achieved by the entrainment of the upstream flow into the pulsating jet. For the on-off application of control, the transient time normalized by the time of flight between the actuator and the trailing edge varies between 15 and 20 over the upper and lower surfaces and between 5 to 15 over the ramp. The possibilities of gradually controlling the airfoil performance are also considered, and the phase delays of the surface-pressure perturbation are discussed.
ASJC Scopus subject areas
- Aerospace Engineering