Phase-averaged characteristics of flow around a circular cylinder under acoustic excitation control

The influence of internal acoustic excitation on the aerodynamic performance of a circular cylinder in a uniform flow is studied by the phase-averaged measurements of fluid forces and flow fields around the cylinder. The experimental results indicate that the mean drag as well as the fluctuating lift are reduced by the acoustic excitation control from a slit on a circular cylinder. The phase-averaged PIV measurements at the vortex shedding frequency show that the periodic and fluctuating velocities are suppressed in the wake of the controlled cylinder, which indicates the influence of acoustic excitation on the vortex shedding and the corresponding reduction in the fluid forces on the circular cylinder. On the other hand, the phase-averaged flow field at the excitation frequency of unstable shear layer, which is four times larger than the vortex shedding frequency, indicates the formation of discrete vortices along the shear layer of the cylinder wake. The interaction of these vortices with the cylinder wake causes the reduction in the cross-correlations of velocity fluctuations in the flow field, which results in the attenuation of the vortex shedding phenomenon in the cylinder wake. (C) 2003 Elsevier Ltd. All rights reserved.