On the cylinder wake subjected to in-phase and out-of-phase periodic forcing

摘要

Experiments were conducted in a wind tunnel to investigate the effect of periodic forcing on the wake of a circular cylinder specially designed for independent control of the phase of forcing from slits located on opposite sides. Tests were conducted at Reynolds number (Re) of 12,000, based on diameter (D). Wake was forced at subharmonic and harmonic frequencies at constant blowing coefficient. Measurements consisted of wake pitot surveys, hotwire anemometry, and Particle Image Velocimetry. A 20% reduction in drag was achieved when the two slits operated in-phase at third harmonic. The drag reduction, however, was 18% when the two slits operated in an out-of-phase mode for the same frequency. Wake lock-in was observed for the out-of-phase forcing case. Wake power spectrum indicated the effectiveness of both types of forcing in suppressing the primary instability. This was also evident from the results of the Proper Orthogonal Decomposition of the PIV data and turbulence statistics.