WIND TUNNEL REMOTE TURBULENCE CHARACTERIZATION (PD-147B)

WE PROPOSE A MONITOR FOR DENSITY FLUCTUATIONS IN THE BOUNDARY LAYER OF TURBULENT FLOWS AROUND TEST OBJECTS IN WIND TUNNELS. THE DIAGNOSTIC IS BASED UPON THE LASER-INDUCED FLUORESCENCE FROM MOLECULAR OXYGEN WHICH IS EXCITED WHEN 193 NM LIGHT FROM AN ARF EXCIMER LASER PROPAGATES THROUGH THE AIR. PARTIAL PREDISSOCIATION GIVES THE EXCITED MOLECULAR OXYGEN A VERY SHORT LIFETIME AND THEREFORE RENDERS IT IMMUNE TO ELECTRONIC QUENCHING. THE INTENSITY OF THE OBSERVED LASER-INDUCED FLUORESCENCE, THEREFORE, IS DIRECTLY PROPORTIONAL TO THE LOCAL NUMBER DENSITY OF THE VOLUME BEING PROBED. DETECTING THIS FLUORESCENCE WITH A TWO-DIMENSIONAL DIODE ARRAY AS THE LASERBEAM SCANS ABOVE THE SURFACE OF THE TEST OBJECT MAPS OUT THE TURBULENCE IN TWO DIMENSIONS. THREE DIMENSIONAL MAPPINGRESULTS FROM REPEATING THE LASER SCANS AT A NUMBER OF DISTANCES ABOVE THE SURFACE OF THE TEST OBJECT. THE OBJECTIVE OF THIS PROPOSAL IS TO DETERMINE QUANTITATIVELY THE FLUORESCENCE YIELD FROM THE EXCITATION, AND THEREBY, THEPOTENTIAL SENSITIVITY OF SUCH A DIAGNOSTIC. PRELIMINARY CALCULATIONS INDICATE A SENSITIVITY TO FLUCTUATIONS BELOW 0.1 PERCENT.