TRACERS AND INSTRUMENTATION FOR VELOCITY MEASUREMENTS IN COMPLEX VERTICAL FIELDS

THE DEFENSE ADVANCED RESEARCH PROJECTS AGENCY (DARPA) HAS IDENTIFIED A NEED FOR NEW INSTRUMENTATION TECHNIQUES CAPABLE OF VELOCITY MEASUREMENTS FOR HIGHLY UNSTEADY, COMPLEX VORTICAL FIELDS CHARACTERISTIC OF FLOW AROUND A SUBMARINE. THIS PROPOSAL, PREPARED IN COLLABORATION WITH THE PRINCETON UNIVERSITY LASER AND APPLIED PHYSICS GROUP, OFFERS A NEW OPTICAL FLOW FIELD DIAGNOSTIC CAPABLE OF THREE-DIMENSIONAL TRACKING OF SPECIFIC FLUID ELEMENTS IN BOTH SPACE AND TIME. THE TECHNIQUE IS READILY PERFORMED IN WATER AND HAS THE POTENTIAL TO BE USED IN LARGE-SCALE FLOW FACILITIES WITH A MINIMUM OF INSTRUMENTAL COMPLEXITY AND IMAGE POST-PROCESSING. MOLECULAR PROBES WILL DESIGN AND SYNTHESIZE NEW PHOTOACTIVATED FLUOROPHORES (PAFS). WHEN A UV LASER BEAM (OR SUITABLE NON-LASER SOURCE) ILLUMINATES A FLOW CONTAINING THE PAF, IT INDUCES A PHOTOCHEMICAL REACTION THAT PERMANENTLY ALTERS THE CHEMICAL STRUCTURE AND ABSORPTION/FLUORESCENCE CHARACTERISTICS OF THE TRACER. THIS EFFECTIVELY "TAGS" THE FLOW WITH AN ARBITRARY PATTERN "WRITTEN" IN WITH THE UV ILLUMINATING OPTICS. THE TEMPORAL AND SPATIAL EVOLUTION OF THIS PATTERN CAN BE TRACKED INDEFINITELY WITH A SECOND, VISIBLE WAVELENGTH "INTERROGATION" LASER BY RECORDING THE TIME-EVOLVING IMAGE SEQUENCE WITH A VIDEO CAMERA. ANTICIPATED BENEFITS/POTENTIAL APPLICATIONS - THE PHANTOMM FLOW TAGGING METHOD OFFERS UNIQUE CAPABILITY FOR OBTAINING QUANTITATIVE VELOCITY DATA IN INCOMPRESSIBLE FLOW FIELDS. IT IS ANTICIPATED THAT A VERY SIGNIFICANT GROUP OF RESEARCHERS, BOTH FEDERALLY-SPONSORED AND GOVERNMENT LABS, IN A VARIETY OF FLUID MECHANIC DISCIPLINES WILL BENEFIT FROM THE DEVELOPMENT OF SUITABLE PROBES. THE CONUNERCIAL POTENTIAL FOR THE LARGE-SCALE MANUFACTURING OF THESE PROBES IS SIGNIFICANT.