This paper explores the control of wall-separated flow on a NACA 63 3 -018 airfoil and a circular cylinder by using the internal acoustic excitation technique. Experimental study of the characteristics of the flow under internally emanating acoustic waves is performed in an open-type, suction wind tunnel. Tests are carried out at the Reynolds number ranging from 6.3 x 10 3 to 5.0 x 10 5 based on the relevant characteristic lengths, the airfoil chord, and the cylinder diameter. The control effectiveness is verified by the measurements of parameters such as the excitation frequency, the excitation level, and the forcing location. Data indicate that the excitation frequency and the forcing location are the key parameters for controlling the separated flow, and the forcing level is the least-effective parameter for the study. As long as the emanating acoustics is "locked in" to the separated shear-layer instability frequency and forcing is applied at the separation point, the separated flow is controlled most effectively. Moreover, the b'ft is increased and the drag reduced dramatically. Nomenclaturecircular cylinder f e = excitation frequency f s = vortex shedding frequency f t = shear layer instability frequency P = static pressure P t -total pressure p tao = total pressure in freestream P^ = static pressure in freestream Re c = Reynolds number based on chord, Re c = U^ C/v Re D = Reynolds number based on diameter, Re D -U^D/v St = Strouhal number, (/,<:/#«,) or (f.D/U^) U^ = freestream velocity X = coordinate along the freestream direction Y = coordinate normal to the freestream direction p = fluid density v = kinematic viscosity a = sound emission angle of the circular cylinder 0 = polar coordinate in the azimuthal direction

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