Phase-locked eduction of vortex shedding in flow behind past and inclined flat plate

Abstract

Flow past an inclined flat plate at an angle of attack of 30° and a Reynolds number of 30 000 is investigated experimentally. The velocity field in the wake is measured with a laser doppler anemometer (LDA) in the region from one plate breadth downstream to three and a half-plate breadths downstream. Controlled forcing is applied to the wake by vibrating the plate in the across-wind direction at a frequency in the middle of the lock-in range. The forcing serves to enhance the regularity and two-dimensionality of vortex shedding from the plate. It also facilitates phase-locked averaging of the LDA data. The LDA bursts are sorted according to their arrival instants relative to a particular phase of the vortex shedding cycles. The phase-averaged velocity results reveal large-scale vortical structures in the wake. Dynamical properties of these structures such as coherent vorticity and Reynolds stress production are discussed. The wake is found to be strongly asymmetric. The flow dynamics in the wake are dominated by a train of counterclockwise vortices shed from the trailing edge of the plate. The development, shedding and subsequent convection of these vortices are studied by following the consecutive phases of the shedding cycle. ©1996 American Institute of Physics.