Flat-plate Turbulent Boundary Layer Documentation And Pulsed-jet Actuator Development

Skin-friction drag acting on the surfaces of land, sea and air vehicles is mainly dueto turbulent boundary layers around them. Effective control of turbulent boundarylayers could reduce the skin-friction drag. A turbulent boundary layer can be dividedinto different regions, each exhibiting unique features. Meanwhile, coherent structures,which play a key role on turbulence production, energy, momentum and masstransportations, can be identified in a turbulent boundary layer. Further investigations tothe turbulent boundary layer may not only improve our understanding of coherentstructure dynamics and flow physics, but also shed light on active control for dragreduction. In order to produce a canonical turbulent boundary layer in wind tunnel andprovide a candidate of actuators for active control, this thesis has focused on thefollowing three parts.The documentation of a turbulent boundary layer produced by a flat plate at zeropressure gradient. Experiments were conducted in wind tunnel at an oncoming velocityU=10m/s. A single-wire hotwire was used to measure the profile of streamwisevelocity U at a location3.1m downstream of the leading edge. Four different trippingswere used. Wall shear stress was estimated based on the Clauser method. Statistics of Uwere calculated, including mean, rms, skewness and flatness. The present data, whennormalized by either outer or inner scales, are in good agreement with the publishedones, thus indicating a fully developed turbulent boundary layer at the measurementlocation. Two-dimensionality of the boundary layer was also confirmed within aspanwise range of z ?6. Moreover, parameters such asRe??Re ?, andH12, andaveraged width, spacing and length of near-wall low-speed streaks were documented.Here shows the development of a pulsed-jet actuator and its characterization. Thepulsed-jet actuator consists of a loudspeaker, a cavity and an exit. Pulsed jet and vortexring can be produced by the actuator once a step driving voltage is applied. Input-outputrelationship, response time, and jet velocity of the actuator were measured at a widerange of driving voltages (0.1~5volt.). Results indicate that the pulsed-jet actuator hasgood performance, in terms of response time and perturbation, and thus is suitable foractive control of a turbulent boundary layer. DNS (Direct Numerical Simulation) about the drag reduction effect of the pulsedjet actuator for the turbulent boundary layer is shown. The turbulent boundary layercurve was chose at an oncoming velocity U=10m/s, and the pulsed jet come from theactuator with the input voltage2volt, that got the54%drag reduction efficiency.