Variation of Wall Shear Stress and Reynolds Stress over a Flat Plate Downstreamof a Boundary Layer Manipulator

摘要

An experiment to measure the variation of wall shear stress and Reynolds stressover a flat plate downstream of a honeycomb manipulator was conducted. Two velocity components of the flow were measured with an X-configured hot-wire probe, and wall shear stress was obtained from a surface differential pressure gauge or surface fence. Unmanipulated boundary layer data was collected at eight different free stream speeds to establish boundary layer characteristics and to calibrate the surface differential pressure gauge by making use of Coles' law of the wall for the mean velocity profile. Manipulated boundary layer data was obtained at three free stream speeds and six manipulator positions. Although manipulator hole size and length remained constant, height was varied to determine the influence of this length scale upon the surface friction coefficient. Manipulated stream and vertical mean and fluctuating velocity profiles and Reynolds stress profiles were compared to their unmanipulated counterparts to map the influence of the manipulator in the streamwise direction. Immediately downstream of the manipulations the transport of turbulent energy to the wall via the working of Reynolds stresses was sharply reduced. Complete restoration of Reynolds stress profiles to unmanipulated form was not observed out to the farthest downstream measurement position. Local drag reduction up to 40% was verified via comparison of the unmanipulated and manipulated friction coefficients obtained from the wall shear stress measurements. Theses. (jhd)