GENERATION OF AN "ARTIFICIAL" BURST IN A TURBULENT BOUNDARY LAYER

IT IS GENERALLY AGREED THAT THE BURSTING PHENOMENON IS THE MOST SIGNIFICANT DYNAMIC EVENT IN A TURBULENT BOUNDARY LAYER. ABOUT 80% OF THE MOMENTUM TRANSFER OCCURS DURING THESE BURSTS. TO REDUCE VISCOUS DRAG, THE PHYSICS AND STRUCTURE OF THESE EVENTS MUST BE FULLY UNDERSTOOD. HOWEVER, PREVIOUS ATTEMPTS TO ACCOMPLISH THIS HAVE BEEN FRUSTRATED BY THE FACT THAT BURSTS OCCUR RANDOMLY IN TIME AND SPACE. IN THE PRESENT STUDY, ARTIFICIAL GENERATION OF A BURSTING EVENT WILL BE ATTEMPTED, THUS CONTROLLING THE TIME AND POSITION OF ITS OCCURRENCE. THE STRUCTURAL DETAILS OF THESE BURSTS WILL BE EDUCED VIA MEASUREMENTS PHASE-LOCKED TO THE ARTIFICIAL EXCITATION. EXPERIMENTS WILL BE CONDUCTED USING A ZERO-PRESSURE GRADIENT BOUNDARY LAYER THAT DEVELOPS ON A FLAT PLATE TOWED IN AN 18-M WATER CHANNEL. FLOW VISUALIZATION AND HOT-FILM MEASUREMENTS WILL BE CONDUCTED TO EDUCE THE TOPOLOGICAL PROPERTIES OF THE ARTIFICIAL BURSTS. THE KNOWLEDGE DEVELOPED THROUGH THIS STUDY MAY PROVIDE A CONCEPTUAL APPROACH TO MODULATING THE FREQUENCY AND STRENGTH OF NATURAL BURSTS, THEREBY REDUCING DRAG.