Near-Wall Flow Measurements Using Frequency-Modulating Filtered Rayleigh Scattering (FM-FRS)

The frequency-modulating filtered Rayleigh scattering (FM-FRS) technique has been developed and applied for the boundary layer measurements. The FM-FRS technique effectively extracts Rayleigh scattering information from noisy low SNR signals caused by intense wall glare. The boundary layer velocity profiles measured by FM-FRS show excellent agreement with an independent pressure probe measurement and the law-of-the-wall, including approximately 100 μ m above the wall. This technique is desirable for the practical applications of the Rayleigh scattering technique for flow diagnostics to regions that were limited due to strong background and low signal-to-noise ratio.