Influence of internal acoustic excitation upon flow passing a circular cylinder

The flow past a circular cylinder under internal acoustic excitation is studied by measurements of the velocity and pressure fields. Acoustic waves are introduced internally from a slot on the surface of the cylinder. Pressure distributions around the cylinder, the pressure drag and lift of the cylinder, the energy spectra of flow structures, and the downstream wake profiles are investigated. Results indicate that the separated shear layers around the cylinder are sensitive to the excitation frequency in the regime of shear-layer instability and to the forcing location around the laminar separation point. The excitation on the cylinder causes an increase in lift and a dramatic reduction in drag. Also, the wake defect profile is narrowed due to the reduction of large-scale vortices to smaller eddies. The vortex shedding frequency is slightly altered when the flow is excited at the effective frequency. The Strouhal number for the most effective excitation is found to be of the order of 1 in the operating Reynolds number range. The result is verified with a flow visualization study using the smoke-wire technique.