Smart Wall for Control of the Burst Cycle of Longitudinal Vortices in TurbulentBoundary Layers

摘要

This work was aimed at developing a 'smart wall' through the integration of anoptical sensor pressure transducer array and an array of miniature magnetic actuators. The pressure transducer array corresponded to one mirror of an interferometer. This mirror was a thin, flexible sheet on which a reflective layer had been vapor deposited. The sheet overlayed an array of small closely spaced holes in the wall surface. The instantaneous pressure was determined over each hole by the spacing of Moire fringes. The fringe patterns over each hole were simultaneously acquired by a ccd-camera (viewing the full field) and frame-grabber connected to a host computer. The processing involved converting the fringe pattern to pressures, using a neural network, and performing spatial filtering to highlight features associated with longitudinal vortices (large streamwise wave lengths and short spanwise wave lengths). As a compliment to this, a 1-D array of hot wire sensors were acquired for the same flow conditions. 2-D space time analysis of the hot-wire data series were used to categorize the most effective actuator settings. These results were compared to those from the optical pressure sensor array. Bridging the two experiments was the development of software for 2-D Fourier, frequency/wave number analysis of the data series. The final part of the work was the development of a wall element which could introduce spanwise periodic distortions in the wall surface. This consisted of a flexible silicon sheet which covered narrow electromagnetic strips. The strips formed a 1-D array with a spanwise spacing which was suitable for the spanwise scale of streamwise vortices which formed in the flow. The strips deflected in response to a computer output which was designed to produce a standing pattern in the flow.