The scope of this dissertation is to develop and apply a non-intrusive molecular Rayleigh scattering diagnostic that is capable of providing time-resolved simultaneous measurements of gas temperature, velocity, and density in unseeded turbulent flows at sampling rates up to 32 kHz. Molecular Rayleigh scattering is elastic light scattering from molecules; the spectrum of Rayleigh scattered light contains information about the gas temperature and velocity of the flow. Additionally, the scattered signal is directly proportional to the molecular number density. These characteristics are utilized in the development of the measurement technique. This dissertation results in the following:
1. Development of a point-based Rayleigh scattering measurement system that provides time-resolved simultaneous measurement of temperature, velocity, and density at sampling rates up to 32 kHz.
2. Numerical modeling of the light scattering and detection process to evaluate uncertainty levels and capabilities of the measurement technique.
3. Validation of the developed measurement system in benchmark flow experiments in which velocity and temperature fluctuations were decoupled and independently forced at various amplitudes and frequencies.
4. Demonstration of simultaneous measurement of all three quantities in an electrically-heated free jet facility at NASA Glenn Research Center.
5. Comparison of Rayleigh scattering measurements in all experiment phases with thermal anemometry measurements.
The experimental measurements are presented in terms of first-order time-series results that are measured directly by the technique, and second-order statistics, such as power spectral density and rms fluctuations, which are calculated from the direct time-resolved quasi-instantaneous measurements. Temperature fluctuation results are compared with constant current anemometry measurements and velocity fluctuation results are compared with constant temperature anemometry measurements. Experiments were performed in air flows with densities ranging from 0.45 to 1.15 kg/m 3, temperatures from 295 K to 775 K, and velocities from 0 to 110 m/s. Accuracies of 0.02 kg/m 3, 5 - 12 K, and 4 - 10 m/s in the mean density, temperature, and velocity measurements were demonstrated, respectively. Fluctuation amplitude measurements of density, temperature, and velocity in the ranges of 0.02 – 0.125 kg/m 3, 5 – 60 K, and 10 – 20 m/s with accuracies better than 0.01 kg/m 3, 3 K, and 7 m/s were achieved, respectively.