SIMULTANEOUS TEMPERATURE, DENSITY, AND FLOW DIAGNOSTICS FOR AEROPROPULSION SYSTEMS

THE DESIGN OF ADVANCED PROPULSION SYSTEMS REQUIRES SIMULTANEOUS MEASUREMENT OF THE FLOW VELOCITIES AND THE THERMODYNAMIC QUANTITIES OF THE GAS IN ORDER TO VERIFY THE MATHEMATICAL MODELS BASED ON THE TIME-AVERAGED NAVIER-STOKES EQUATIONS. THE DEVELOPMENT OF THE COHERENT ANTI-STOKES RAMAN SCATTERING (CARS) TECHNIQUE HAS MADE POSSIBLE THE MEASUREMENT OF THE TEMPERATURE AND THE PRESSURE OF THE FLOW, BUT WITHOUT VELOCITY INFORMATION. THE CONVENTIONAL LASER DOPPLER VELOCIMETRY TECHNIQUE IS INCAPABLE OF SUPPLYING INFORMATION AT THE REQUIRED LEVEL OF DETAIL BECAUSE THE MEASURED DUST PARTICLES NO LONGER FOLLOW THE FLOW LINES AT HIGH VELOCITIES. OUR OBJECTIVE IS TO COMBINE CARS WITH A WELL KNOWN SPECTROSCOPIC TECHNIQUE, STIMULATED BRILLOUIN SCATTERING (SBS) WHICH CAN MEASURE FLOW VELOCITY FROM SUBSONIC THROUGH HYPERSONIC SPEEDS. NO ADDITIONAL LASERS ARE NEEDED SINCE THE CARS LASERS THEMSELVES CAN BE USED TO PRODUCE AN SBS SIGNAL. BY ADDING A DETECTION SYSTEM AND CHANGING THE CARS GEOMETRY SLIGHTLY, ONE CAN OBTAIN MEASUREMENTS OF ALL THE KEY PARAMETERS OF THE FLOW (VELOCITY, TEMPERATURE, DENSITY) IN A SINGLE STOP-MOTION LASER PULSE. THE AVAILABILITY OF SIMULTANEOUS MEASUREMENTS IS REQUIRED FOR THE COMPARISON WITH THE TIME AVERAGED THEORY WHICH DEALS WITH THE INSTANTANEOUS CORRELATIONS BETWEEN PAIRS OF THERMODYNAMIC VARIABLES. WE PLAN TO INVESTIGATE THE COMPATIBILITY OF CARS AND SBS, AND TO DESIGN A PROTOTYPE SYSTEM WHICH WE WILL USE IN THE PHASE II PROGRAM TO VERIFY THE PERFORMANCE OF THE COMBINED SYSTEM.