Experimental Study On The Control Of Oscillation Cylinder Wake

A narrow strip element was applied in the wake of a circular cylinderoscillating inline with the on-coming stream to suppress vortex shedding and reducemean drag and fluctuating forces on the cylinder. The thickness of the strip was verysmall, its surface was perpendicular to the on-coming stream. The control parameterswere scale and position of the element. The experiment was carried out in a windtunnel, and the test ranges of Reynolds number, the non-dimensional frequency ofoscillation, and the experiment parameters were: Re=1.0×104~1.8×104, A/D=0.2,feD/V=0.0~0.2, and b/D=0.13~0.26respectively, where V is the velocity of theon-coming stream, D is the diameter of the cylinder, and is the kinematic viscosityof the air.Three kinds of flow measurement technologies were used: hot-wiremeasurement, electronic scanning valve measurement and smoke-wire flowvisualization.Hot-wire experiment mainly get the cross-section flow velocity whichdownstream of the oscillating cylinder5D with or without an element. Results ofspectra analysis of fluctuating velocities in the wake showed that, a non-lock-onmode and three lock-on modes of vortex shedding were observed in the wakewithout control. The non-lock-on mode and two lock-on modes of vortex sheddingcan be suppressed if the element was set in certain regions, but one lock-on modes(feD/V=0.12~0.16) of vortex shedding cannot be suppressed.Pressure experiment mainly measured pressure distribution on the surface ofoscillating cylinder with or without an element. Results of spectra analysis offluctuating lift on the cylinder confirmed the results of hot-wire measurement.Effective zones of the element were found according to the results. The effectivezone changed with the changes of Reynolds number, oscillation frequency and scaleof the element, but for a certain mode of vortex shedding, the center position of theeffective zone was nearly fixed. Measurements showed that, the application of theelement could reduce the mean drag and fluctuating forces at every modes of vortex shedding.Pictures of smoke-wire flow visualization showed the wake of oscillatingcircular cylinder with and without narrow strip element.Results show that, vortex shedding can be suppressed if the element is set in acertain region referred to as effective zone. The drag and lift of the cylinder can bereduced by the application of the element.