Control of laminar separation over airfoils by acoustic excitation

Interaction Between Vortex Rings and a Separated Shear Layer: Towards Active Control of Separation Zones

“…The drag is also expected to attain a minimum value at the same frequency because the height of the separated zone becomes minimum. This frequency when normalized in the form F N c/; is in a range of 3}4 (Zaman & McKinzie 1991;Zaman 1992), 1}3 (Hsiao et al, 1989) and 2 (Bar-Sever 1989), being of the same order as the abovementioned frequency Fc/; "4. At high Reynolds numbers the frequency F N is much lower than the fundamental frequency of Kelvin}Helmholtz (K}H) instability in the separated shear layer F )& (Zaman 1992).…”

“…Periodic forcing of stalled #ow around two-dimensional airfoils yields a particular forcing frequency, F N at which the lift attains a maximum (Hsiao et al, 1989;Bar-Sever 1989;Zaman & McKinzie 1991;Zaman 1992). The drag is also expected to attain a minimum value at the same frequency because the height of the separated zone becomes minimum.…”

Low Reynolds Number Flows and Transition

“…Also they indicated that when boundary layer separation occurs without reattachment, the increase of the excitation amplitude above the minimum threshold leads a separation bubble formation with delayed boundary layer separation. Zaman & McKinzie (1991) investigated the effects of acoustic excitation in reducing the adverse influences of the LSB over two dimensional aerofoils at low angles of attack by using smoke wire visualization and hot wire anemometry. They studied in the chord based Re number range of 2.5x10 4 <Re c <1x10 5 .…”

Experimental Study on the Separation Control of Turbulent Boundary Layers by Vortex Excitation

“…Indeed, several experiments have successfully suppressed large separation bubble on an airfoil. [3][4][5][6][7] In the case of weak external disturbances, it is expected that the most amplified wave for the linear instability is effective in controlling separation when the separation bubble is not very large. However, when strong forcing is applied to suppress the large separation bubble, the scale of the most effective disturbance is larger than that of the most amplified disturbance and is comparable to the height of the separation bubble.…”