Experimental Study On The Control Of Wake Behind A Rotary Oscillating Plate

When the fluid flows across a bluff object, the vortex shedding alternatively can occur behind the object and cause the pressure on the surface of the object to change. The periodic force makes the object vibrate and destroys the structure of object. In this paper, the rotary oscillating plate is the simplified model of wind blowing across the bridge span structure. Therefore, studying the wake from a rotary oscillating plate and wake control problem have a great significance on protection of bridges, high-rise buildings and so on.The methods of double strip elements and base blowing are used to suppress the wake of a rotary oscillating plate at Reynolds numbers Re=V∞H/v = 2.5x103~6.0x103, oscillation amplitude θ=10°, and oscillation frequencies feH/V∞=0~0.123. At equilibrium position of the oscillation, the main surface of the plate is parallel to the on-coming stream. One non-lock-on mode and three lock-on modes of vortex shedding are observed in the wake without control. In element experiment, two strip elements of equal size are placed symmetrically on the upper and lower sides of the plate, and the main surfaces of the strips are perpendicular to the on-coming stream. The ratio of the strip width to plate thickness b/H is 1/3. The results of velocity fluctuation measurement and wake flow visualization in a wind tunnel show that, the non-lock-on mode and two lock-on modes of vortex shedding can be suppressed if the elements are placed in effective zones. The influences of Reynolds number and oscillation frequency on the effective zones are investigated. In base blowing experiment, air jet is blown out from a span-wise slit of width 1mm at the rear surface of the plate. The control parameter is the relative blow velocity. Experimental results indicate that, the non-lock-on mode and one lock-on mode of vortex shedding can be suppressed when the blow velocity is in effective ranges.