Molecular Rayleigh scattering is a technique that can measure density, velocity, and temperature fluctuations in supersonic wind tunnels. It works by passing a laser through the wind tunnel and analyzing the scattered light. This provides a non-intrusive way to obtain fundamental flow property measurements without disturbing the flow. The proposal seeks to demonstrate this technique's capabilities to measure thermal boundary layer and wake fluctuations in a research wind tunnel, with the goal of advancing the technique's readiness level from 2 to 5. This could help understand issues like buffet, acoustics, and shock oscillations on aerospace vehicles tested in wind tunnels.

1. Molecular Rayleigh Scattering to measure fluctuations in density, velocity and
temperature in wind tunnels
Innovation Jay Panda (ARC-AOX), jayanta.panda-1@nasa.gov
Spectrum of turbulent fluctuations
DESCRIPTION
QUANTITATIVE IMPACT
in supersonic and transonic wind
tunnels can not be measured
STATUS QUO
CONCEPT DESCRIPTION: Potential customers and
Problem: spectrum of turbulent The molecular Rayleigh scattering technique provides the Applications:
fluctuations in supersonic flows, most fundamental way of measuring flow properties: bulk Transonic and supersonic wind
especially across shock-waves in density via measuring molecular number density, bulk tunnels of NASA, Industry and
wind tunnel models cannot be velocity via measuring the central peak in the distribution academia can use this
measured. of molecular speed, and temperature via measuring the technique to determine
Current solution: full-width at half-maxima of that distribution. However, the causes and impact of buffet,
scattered light intensity is very weak. The present goal is acoustics, shock oscillation
particle image velocimetry can neither a proof-of-concept demonstration in a low-speed and transition over aerospace
measure spectrum of velocity research wind tunnel. vehicles.
fluctuations nor any scalar fluctuations
HOW IT WORKS: Quantitative metrics:
Proposed solution:Particle-free, non- For the proof-of-concept
intrusive, Molecular Rayleigh A narrow line-width continuous wave laser will be passed
through the wind tunnel test section, and light scattered demonstration we will measure
scattering based technique to temperature fluctuations in
simultaneously measure density, by gas molecules from a point on the beam will be
collected and analyzed using a Fabry-Perot thermal boundary layer over a
velocity and temperature fluctuations heated plate, and in the wake
interferometer. Optical spectrum analysis over small time
Starting TRL: 2 intervals will provide measures of velocity and static of a bluff body in a research
temperature fluctuations as a function of time. The tunnel.
fluctuations in air density will be determined by
Key new insights:
END-OF-TASK OBJECTIVES
monitoring the intensity variations of the scattered light
using photo-multiplier tubes.
ASSUMPTIONS AND LIMITATIONS: Deliverables: : Demonstration of
Significance technique in a research wind tunnel
NEW INSIGHTS
Recently Rayleigh scattering has Wind tunnel environments provide significant challenges for
Start-end TRL: 2-5
been advanced for flow the insertion of alaser beam,
measurements in supersonic free Team:
containment of specular and Jay Panda, AOX, 4-1553, PI
jets, but challenges of confined
walls in wind-tunnels have not diffused reflection, removal of Steve Schery, AOX, 4-0741,
been overcome. dust particles, and providing Associate
Your role: adequate vibration isolation. Follow-on work:
I have extensive background from Setting up at Ames 11-ft and 9X7
Present effort is to overcome wind tunnel. This will require
12+ years of work on Rayleigh
scattering at NASA Glenn these challenges support from Aeronautics Test
CONCEPT IMAGE> Program (ATP)
Molecular Rayleigh scattering can bring unprecedented measurement capabilities
to transonic and supersonic wind tunnels