Developments in signal analysis for laser Rayleigh scattering

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Abstract
Digital techniques are presented for filtering particle scatter contributions to laser Rayleigh scattering signals. The filter methods follow from criteria based on particle scatter characteristics and allow differentiating between molecular and particle scatter contributions to the measured signal. Use of the techniques reported allow for Rayleigh scattering measurements in flows where particles are present. Measurements of mean and RMS mole fraction distributions are presented for a free jet and the results for the mean compare with those obtained from a sampling probe and indicate uncertainty in the mean to be within 2% of unity. For the RMS results, particle scatter is shown to lead to overprediction when the Rayleigh signals are unfiltered but the problem can be circumvented to a significant degree by the methods described. It is concluded that particle scatter contributions to laser Rayleigh scattering signals cannot, in some instances, be associated with any criteria which allow their removal.