THIS INVESTIGATION IS AIMED AT DEVELOPING AN ACTIVE FLOW CONTROL DEVICE TO GENERATE LARGE-SCALE, PERIODIC STRUCTURES IN A TURBULENT SHEAR FLOW.

THIS INVESTIGATION IS AIMED AT DEVELOPING AN ACTIVE FLOW CONTROL DEVICE TO GENERATE LARGE-SCALE, PERIODIC STRUCTURES IN A TURBULENT SHEAR FLOW. THE DEVICE WILL BE USED ON AIRBORNE LASER PLATFORMS TO REDUCE OR ELIMINATE OPTICAL DISTORTION OF THE LASER BEAM CAUSED BY THE TURBULENCE. CONTROLLED EXPERIMENTS WILL BE CONDUCTED IN AN 18-METER TOWING TANK TO INVESTIGATE THE FEASIBILITY OF GENERATING LARGE-SCALE, PERIODIC STRUCTURES IN A HIGHLY TURBULENT FLOW FIELD. TWO METHODS ARE PROPOSED FOR ALTERING THE TURBULENCESTRUCTURE. THE FIRST IS THE USE OF A CONTROLLED CYCLIC JET ISSUING FROM THE WALL OF A BOUNDARY LAYER TO COLLECT THE TURBULENCE FOR A FINITE TIME AND THE RELEASE ALL OF THE ENERGY INSTANTANEOUSLY IN ONE LARGE EDDY THAT CONVECTS DOWNSTREAM. THE SECOND METHOD INVOLVES A TURRET-LIKE DEVICETO DIVERT THE AIRPLANE'S BOUNDARY LAYER AWAY FROM THE PATH OF THE LASER BEAM. THE RESULTING FREE SHEAR LAYER WILL THENBE ACTIVELY CONTROLLED BY SUBHARMONIC PERTURBATION. BOTH DEVICES WILL BE TESTED AND OPTIMIZED ON A ZERO PRESSURE-GRADIENT BOUNDARY LAYER USING NOVEL FLOW VISUALIZATION TECHNIQUES AND FAST-RESPONSE VELOCITY PROBE MEASUREMENTS. CONDITIONAL SAMPLING AND PATTERN RECOGNITION TECHNIQUES WILL BE USED TO ANALYZE THE RANDOM VELOCITY SIGNAL.