Multiproperty Measurements at High Sampling Rates Using Rayleigh Scattering

A molecular Rayleigh scattering technique is developed to measure gas velocity, temperature, and density in unseeded gas flows at sampling rates up to 32 kHz. A high-power continuous-wave laser beam is focused at a point in an air flowfield, and Rayleigh scattered light is collected and fiber-optically transmitted to a Fabry-Perot interferometer for spectral analysis. Photomultiplier tubes operated in the photon-counting mode allow high-frequency sampling of the total signal level and the circular interference pattern to provide density, temperature, and velocity measurements. Mean and root-mean-square fluctuation measurements in both an electrically heated jet facility with a 10-mm-diam nozzle and in a hydrogen-combustor-heated-jet facility with a 50.8-mm-diam nozzle at NASA John H. Glenn Research Center at Lewis Field are presented. Measurements are compared with hot-wire anemometry, cold-wire thermometry, and temporally resolved particle image velocimetry to validate the Rayleigh technique.