Spatially-and temporally-resolved multi-parameter interferometric rayleigh scattering system and method
Inventors
Bivolaru, Daniel • Cutler, Andrew D. • Danehy, Paul M.
Assignees
George Washington University • National Aeronautics and Space Administration NASA
Publication Number
US-8976351-B2
Publication Date
2015-03-10
Expiration Date
2031-05-06
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Abstract
A system that simultaneously measures the translational temperature, bulk velocity, and density in gases by collecting, referencing, and analyzing nanosecond time-scale Rayleigh scattered light from molecules is described. A narrow-band pulsed laser source is used to probe two largely separated measurement locations, one of which is used for reference. The elastically scattered photons containing information from both measurement locations are collected at the same time and analyzed spectrally using a planar Fabry-Perot interferometer. A practical means of referencing the measurement of velocity using the laser frequency, and the density and temperature using the information from the reference measurement location maintained at constant properties is provided.
Core Innovation
The invention provides a system and method for spatially and temporally resolved multi-parameter interferometric Rayleigh scattering (IRS) to simultaneously measure translational temperature, bulk velocity, and density in gases by collecting, referencing, and analyzing nanosecond time-scale Rayleigh scattered light from molecules. It utilizes a narrow-band pulsed laser source to probe two largely separated measurement locations, with one location serving as a reference. The elastically scattered photons from both locations are collected simultaneously and spectrally analyzed using a planar Fabry-Perot interferometer, providing a practical means of referencing velocity measurements using the laser frequency and the density and temperature measurements using the reference location maintained at constant properties.
The problem addressed by the invention arises from the critical need for molecular-based diagnostic techniques capable of obtaining simultaneous multiple fluid properties such as temperature, density, and velocity with spatial resolutions of hundreds of microns or less and temporal resolutions of hundreds of nanoseconds or less. Previously, no single diagnostic technique could meet these requirements for simultaneous measurements in gases, especially at elevated temperatures and various flow regimes, including subsonic, supersonic, and hypersonic flows. Earlier approaches using linear optical techniques such as IRS and nonlinear techniques like CARS (coherent anti-Stokes Raman spectroscopy) were limited in precision, scope, or simultaneous measurement capabilities for density and translational temperature from IRS.
The invention thus provides a non-intrusive optical diagnostic system employing a seeded dual Nd:YAG narrow-band pulsed laser source at 532 nm wavelength, combined with a beam combiner, polarization dependent beam splitter, and a planar Fabry-Perot interferometer to collect and analyze Rayleigh scattered signals from two locations concurrently. It introduces an optical setup to normalize measured signals against those from a reference cell with known gas properties, thus correcting for laser energy fluctuations and providing referencing for gas density, temperature, and velocity. A simplified Gaussian-Lorentzian spectral model is used with corrections applied for deviations at lower gas temperatures. The system demonstrates capability in measuring flame properties in an H2-air Hencken burner flame compared to adiabatic flame theory predictions and can operate over a wide range of temperatures (cryogenic to about 2500 K), densities (0.1 to about 2 kg/m³), and velocities (up to ±1.5 km/s or 3 km/s with directional knowledge).
Claims Coverage
The patent contains multiple independent claims defining inventive features of a closed-loop optical system for multi-parameter analysis of gaseous media.
Multi-parameter gas analysis system with dual-location probing
A system comprising a narrow-band pulsed laser source probing both a measurement location and a reference location in the gaseous media; optical elements collecting scattered light from these locations; and a beam combiner optically mixing the scattered light and unscattered light reference signals to facilitate simultaneous analysis.
Spectral analysis instrumentation with Fabry-Perot interferometer and CCD imaging
Integration of a Fabry-Perot interferometer receiving the mixed light signals followed by a CCD camera imaging system to spectrally analyze the interferometric signals for deriving gas properties.
Signal recycling multi-interferometer optical configuration
An optical arrangement employing two Fabry-Perot interferometers oriented perpendicularly, combined with a quarter-wave plate to recycle the scattered light polarization and extend the velocity measurement dynamic range and accuracy by mixing high and low spectral resolution interferometers.
Optical assembly including beam reducers and polarization-dependent beam combiner
A detailed construction of the system using first and second beam reducers/expanders, polarization dependent beam combiner, and a series of lenses and mirrors to focus, collect, and direct scattered light from gaseous samples and a reference volume to the interferometers for measurement.
These inventive features collectively define a system for simultaneous multi-parameter optical diagnostics of gaseous flows by probing both measurement and reference locations with scattered and unscattered laser light, spectrally analyzed through Fabry-Perot interferometry enhanced by signal recycling configurations and beam combining optics, enhancing accuracy, referencing, and dynamic measurement range.
Stated Advantages
Simultaneous non-intrusive measurement of translational temperature, bulk velocity, and density in gases with high spatial and temporal resolution.
Practical referencing with a reference measurement location of known properties to correct for laser energy fluctuations and provide calibration for velocity, temperature, and density measurements.
Capability to measure over a wide range of temperatures (cryogenic up to about 2500 K), gas densities, and velocities including supersonic and hypersonic regimes up to 3 km/s.
Improved measurement accuracy by using signal recycling with dual interferometers to remove velocity sign ambiguity and extend dynamic range while providing high spectral resolution.
Documented Applications
Characterizing flows within airbreathing engines such as scramjet and scramjet-turbine combined cycle engines for hypervelocity vehicles.
Studying turbulent fluctuations and mean fluid properties for development of turbulence models and aircraft noise prediction tools in subsonic aircraft.
Measurement and diagnostics of reacting and non-reacting gaseous flows, including flames such as H2-air combustion flames under near-adiabatic conditions.
Simultaneous multi-property turbulence studies of subsonic, supersonic, and hypersonic nonreacting flows and predictable composition reacting flows.
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