Time-Resolved Rayleigh Scattering Measurements in Hot Gas Flows

Abstract

[Abstract] A molecular Rayleigh scattering technique is developed to measure timeresolved 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 flow field and Rayleigh scattered light is collected and fiber-optically transmitted to the spectral analysis and detection equipment. The spectrum of the light, which contains information about the temperature and velocity of the flow, is analyzed using a Fabry-Perot interferometer. Photomultipler tubes operated in the photon counting mode allow high frequency sampling of the circular interference pattern to provide time-resolved flow property measurements. Mean and rms velocity and temperature fluctuation measurements in both an electrically-heated jet facility with a 10-mm diameter nozzle and also in a hydrogen-combustor heated jet facility with a 50.8-mm diameter nozzle at NASA Glenn Research Center are presented.

Analysis and design of imaging Fabry-Perot interferometers for measurement of Rayleigh-Brillouin scattering spectra in gas flows

“…Laser Rayleigh-Brillouin scattering provides an effective method for non-intrusive measurement of gas flow properties [1][2][3][4][5][6][7][8][9][10][11][12][13]. The received scattered laser light power is proportional to the gas density, the linewidth of the Rayleigh-Brillouin scattering spectrum is related to the gas temperature, and the Doppler frequency shift of the peak of the RayleighBrillouin scattering spectrum is related to the gas velocity.…”

“…The measurement of gas flow's properties relies on the exact knowledge of the spectral profile of the scattered light. The Rayleigh-Brillouin scattering spectra can be acquired by a Fabry-Perot interferometer operated in the imaging mode where an intensified CCD camera is frequently used to record the interference patterns of the Fabry-Perot interferometer [3][4][5][6][7][8][9][10][11][12][13]. The Rayleigh-Brillouin scattering spectrum is then reconstructed from the measured data deconvolved with the Fabry-Perot instrument function.…”

Progress on a Rayleigh Scattering Mass Flux Measurement Technique

“…Seasholtz et al 4 made velocity measurements in a supersonic wind tunnel where they used an iodine absorption filter to remove unwanted stray laser light. Our research group at NASA Glenn Research Center (GRC) has developed several fiber-coupled point-wise Rayleigh scattering measurement systems that are capable of acquiring data at high sampling rates using high quantum efficiency detectors [5][6][7] R . In most of our previous work an air-spaced FP interferometer was used to measure the Rayleigh spectrum.…”

Multiple-Point Mass Flux Measurement System Using Rayleigh Scattering

“…The instrumentation under development is planned for use in the 15 cm x 15 cm supersonic wind tunnel at NASA Glenn Research Center. In order to provide spatially-resolved measurements using direct-imaging of the laser beam a solid Fabry-Perot etalon is used rather than the adjustable air-spaced FP interferometer used in previous work [8][9][10] to avoid degradation of the signal due to vibration of the individual plates in the harsh environment of the facility. For this preliminary work at low data acquisition rates, a low read-noise CCD camera is used to record the image of an 18 Watt 532 nm laser beam filtered by the FP etalon.…”

“…Using an optical fiber to collect the Rayleigh scattered light provides point-wise or spatially-averaged measurements over a finite distance (on the order of 1.0 mm) along a focused laser beam. Our research group at NASA Glenn Research Center has developed several fibercoupled point-wise Rayleigh scattering measurement systems that are capable of acquiring data at high sampling rates using high quantum efficiency detectors [8][9][10] . Although single-point time-resolved measurements are quite useful, there are many situations that would benefit from multiple-point measurements, especially if these can be acquired at high sampling rates.…”