Aerodynamics of a circular cylinder in oscillatory flow.

Abstract

Experimental investigations of the aerodynamics of a circular cylinder in oscillating flow have been made at Reynolds numbers of (1.1∼1.7)×104. The vortex-shedding frequencies, time mean and fluctuating pressure distributions on a cylinder in sinusoidal gusts with various frequencies and amplitudes have been obtained. Fluctuating fluid forces acting on a cylinder have been separated into two parts, i. e., and oscillating fluid force due to vortex shedding and that due to the flow oscillation, using a computer-aided flow visualization technique. The lock-on phenomena occur in the frequency ranges near the natural vortex-shedding frequency and at twice this value. The alternative nature of vortex shedding is maintained in both locked and unlocked conditions, but an appreciable increase in an oscillating lift force appears in locked-on ranges. The oscillating lift and drag forces due to flow oscillation are proportional to the gust velocity components in their individual directions.