Empirically mapping the sensitivity of filtered Rayleigh scattering for multi-parameter measurements in high temperature flows

It is shown that the precision of multi-flow field parameter estimation with frequency-scanning filtered Rayleigh scattering (FSM-FRS) degrades at high temperature due to the Doppler broadening of the Rayleigh scattering signal. This is shown in FRS measurements acquired on a high-temperature reacting flow facility with total temperatures up to 1300 K and Mach 0.3, validated against a thermocouple. Through singular value decomposition of the FRS model as well as examination of the Fisher information matrix, error covariance, and parameter uncertainty estimates, the signal broadening is linked to a reduction in parameter sensitivity and parameter cross-sensitivity. The resulting loss in precision manifests as an error of up to 33% when compared against the probe in the high signal broadening regime. Therefore, it is recommended to increase the number of frequency scanning points FRS measurements are taken at to increase Fisher information and thus improve parameter estimation, or avoid measurement setups with high amounts of Doppler broadening.