molecular rayleigh scattering to measure fluctuations in density, velocity and temperature in wind...
TRANSCRIPT
Potential customers and Applications:Transonic and supersonic wind tunnels of NASA, Industry and academia can use this technique to determine causes and impact of buffet, acoustics, shock oscillation and transition over aerospace vehicles.
Quantitative metrics:For the proof-of-concept demonstration we will measure temperature fluctuations in thermal boundary layer over a heated plate, and in the wake of a bluff body in a research tunnel.
Significance
Recently Rayleigh scattering has been advanced for flow measurements in supersonic free jets, but challenges of confined walls in wind-tunnels have not been overcome.
Your role:I have extensive background from 12+ years of work on Rayleigh scattering at NASA Glenn
Molecular Rayleigh scattering can bring unprecedented measurement capabilities to transonic and supersonic wind tunnels
CONCEPT DESCRIPTION:
The molecular Rayleigh scattering technique provides the most fundamental way of measuring flow properties: bulk density via measuring molecular number density, bulk velocity via measuring the central peak in the distribution of molecular speed, and temperature via measuring the full-width at half-maxima of that distribution. However, the scattered light intensity is very weak. The present goal is a proof-of-concept demonstration in a low-speed research wind tunnel.
HOW IT WORKS:
A narrow line-width continuous wave laser will be passed through the wind tunnel test section, and light scattered by gas molecules from a point on the beam will be collected and analyzed using a Fabry-Perot interferometer. Optical spectrum analysis over small time intervals will provide measures of velocity and static temperature fluctuations as a function of time. The fluctuations in air density will be determined by monitoring the intensity variations of the scattered light using photo-multiplier tubes.
ASSUMPTIONS AND LIMITATIONS:
Wind tunnel environments provide significant challenges for the insertion of alaser beam,
containment of specular and
diffused reflection, removal of
dust particles, and providing
adequate vibration isolation.
Present effort is to overcome
these challenges
CONCEPT IMAGE>
Deliverables: : Demonstration of technique in a research wind tunnel
Start-end TRL: 2-5
Team:Jay Panda, AOX, 4-1553, PI
Steve Schery, AOX, 4-0741, Associate
Follow-on work:Setting up at Ames 11-ft and 9X7 wind tunnel. This will require support from Aeronautics Test Program (ATP)
Spectrum of turbulent fluctuations in supersonic and transonic wind tunnels can not be measured
Key new insights:
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SMolecular Rayleigh Scattering to measure fluctuations in density, velocity and
temperature in wind tunnelsInnovation Jay Panda (ARC-AOX), [email protected]
Problem: spectrum of turbulent fluctuations in supersonic flows, especially across shock-waves in wind tunnel models cannot be measured.
Current solution:
particle image velocimetry can neither measure spectrum of velocity fluctuations nor any scalar fluctuations
Proposed solution:Particle-free, non-intrusive, Molecular Rayleigh scattering based technique to simultaneously measure density, velocity and temperature fluctuations
Starting TRL: 2