Interferometric Rayleigh Scattering for Flow Temperature and Velocity Analysis

A new processing method is developed to analyze images from a Fabry–Pérot interferometer in order to extract point measurements of temperature and velocity within a gas flow, using Rayleigh scattering. Two types of interferograms are generated from a Fabry–Pérot model combined with a simulated light source. The first type is obtained from a diffuse coherent light source, namely, a laser beam on a diffuser. The interferometer characteristics, defined by only two independent parameters, are retrieved within 0.1% accuracy. The knowledge of these parameters is mandatory to analyze interferograms from Rayleigh scattered light. The second type corresponds to Rayleigh scattered light from a small volume under flow conditions, lighted with a focused laser beam and captured with long exposure time. Several flow parameters are chosen to generate these interferograms. The relative errors on the temperature and velocity estimates are found to be weak. Noise is also added to assess the robustness of the processing method. The error induced by the estimates of the instrument function is found to be of second order compared to the error induced by the image analysis.