On amplitude scaling of active separation control

Various scaling options for the effects of excitation magnitude on the lift alternation due to zero-mass-flux periodic excitation for boundary layer separation control are examined. Physical scaling analysis leads to five amplitude parameters. The different scaling laws are examined using experimental data acquired at low Reynolds numbers and various angles of attack. The results indicate that both the velocity ratio and the momentum coefficient, commonly used for amplitude scaling of separation control applications, do not scale the current data-set. For 2D excitation with a Strouhal number of order unity, a Reynolds weighted momentum coefficient provides reasonable scaling. For 3D excitation with a Strouhal number greater than 10, the Reynolds scaled momentum coefficient, the Strouhal scaled velocity ratio and the newly defined vorticity-flux coefficient, all provide good scaling. The airfoil incidence variations are accounted for by using the velocity at the boundary layer edge at the actuation location, rather than the fixed free-stream velocity as a velocity scale. The main finding of this study is that the Reynolds number scaled momentum coefficient provides good amplitude scaling for the entire current data set.