Development and demonstration of filtered Rayleigh scattering: A laser based flow diagnostic for planar measurement of velocity, temperature and pressure

This dissertation presents a laser based flow field diagnostic technique called Filtered Rayleigh Scattering (FRS), and demonstrates its capability for flow visualization and planar measurement of velocity, temperature and pressure. The technique uses a tunable, narrow linewidth laser to induce Rayleigh-Brillouin scattering from the molecules of a gaseous flow. By passing this scattered light through a narrow bandwidth optical notch filter, based on an absorption line of iodine vapor, the scattering is spectrally resolved. This allows for the determination of the Rayleigh-Brillouin lineshape and the Doppler shift. Flow temperature and pressure are then determined from the spectral lineshape, while velocity is determined from the Doppler shift. High quality flow visualization is achieved by using the spectral filter to block stray scattering, while transmitting most of the scattering from the flow.; Key elements of the dissertation include: (1) development of a model for the scattering and detection processes involved in FRS, (2) evaluation of the effects of signal collection over a large solid collection angle, (3) theoretical and experimental characterization of the molecular iodine absorption filter, (4) assembly of a working FRS system, including a subsystem for the accurate measurement of laser frequencies, (5) demonstration of FRS for flow visualization, and (6) demonstration of FRS for planar measurements of velocity, temperature and pressure.; The flow visualization capabilities of FRS were demonstrated in the boundary layer of a Mach 3 wind tunnel, in a Mach 5 free jet, and inside of a supersonic jet inlet model. The use of FRS for time-averaged planar measurements of velocity, temperature and pressure was demonstrated in ambient air and in a Mach 2 free jet. In both cases, accuracies better than or equal to +/{dollar}-{dollar} 3% and +/{dollar}-{dollar} 6% were achieved for temperature and pressure, respectively. Velocity measurements indicated the presence of an error due to a previously unknown variation in frequency across the laser beam. Using a simple calibration scheme, the Mach 2 velocity measurements were accurate to +/{dollar}-{dollar} 5 m/s (+/{dollar}-{dollar} 3%). It was shown that by removing or better calibrating this error source, absolute measurement uncertainties of +/{dollar}-{dollar} 2 m/s are attainable.