AN OPTICAL METHOD FOR ACCURATE MEASUREMENT OF PARTICLE TRAJECTORIES IN HIGH-SPEED FLOWS

THE DEVELOPMENT OF AN OPTICAL METHOD IS PROPOSED FOR THE IMMEDIATE APPLICATION OF INVESTIGATING THE EFFECTS OF SMALL PARTICLES ON THE EVOLUTION OF A LAMINAR BOUNDARY LAYER FORMED AS FLOW PASSES THE NOSE OF AN UNDERWATER VEHICLE. DURING PHASE I, WE WILL DEMONSTRATE THE FEASIBILITY OF DEVELOPING SUCH A METHOD. A TWO-DIMENSIONAL FLOW FACILITY, WITH A STREAMLINED OBSTACLE TO SIMULATE THE FLOW PAST AN UNDERWATER VEHICLES, WILL BE ASSEMBLED FOR THE PHASE I DEMONSTRATION. NEARLY NEUTRALLY BUOYANT MICROCAPSULES FILLED WITH A FLUORESCENT DYE SOLUTION WILL BE USED AS THE PARTICLES. A SHEET OF LASER LIGHT WILL ILLUMINATE THE FLOW FIELD. THE POSITIONS AND THUS THE TRAJECTORIES OF THE PARTICLES WILL BE RECORDED WITH A TWO-DIMENSIONAL PHOTODIODE ARRAY CAMERA CONSISTING OF 128 X 128 PIXELS. TO MAXIMIZE THE FIELD OF VIEW WITHOUT SACRIFICING THE RESOLUTION, WE WILL INTENTIONALLY BLURR THE IMAGES OF THE PARTICLES TO COVER 10 TO 20 PIXELS, WHICH HAS BEEN SHOWN TO IMPROVE SIGNFICANTLY THE RESOLUTION OF THE ARRAY CAMERA. UP TO 10 FRAMES OF CAMERA OUTPUT WILL BE STORED ON FAST STATIC RAM CHIPS VIA A FLASH ANALOG-TO-DIGITAL INTERFACE. THE DATA WILL BE TRANSFERRED TO A HARD DISK OF A MICROCOMPUTER. SOFTWARE WILL BE DEVELOPED FOR DATA ACQUISITION AND ANALYSIS TO DETERMINE THE PARTICLE TRAJECTORIES, VELOCITIES AND ACCELERATIONS. EXTENSION OF THE METHOD TO MEASUREMENTS IN A THREE-DIMENSIONAL FLOW FIELD MAY BE MADE IN PHASE II BY USING A TWO-CAMERA STEREOSCOPIC SYSTEM.