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Laser Rayleigh Scattering for Flow Density and Condensation Measurements in the Supercooled Mach-14 Free-Stream at AEDC Wind Tunnel No. 9Laser Rayleigh scattering was used to investigate clusters in the free-stream flow at Arnold Engineering Development Center’s Tunnel 9 (T9). The facility was run at Mach-14, with a pure-N2 flow medium, and at several total pressures and temperatures. Using an excimer laser operating at 248 nm, the Rayleigh instrument imaged scattering from the focused laser beam in the free-stream. As a wind-tunnel flow is accelerated, it cools and approaches the condensation boundary. As a precursor to condensation, small clusters of molecules are first formed, but the individual clusters are too small to be spatially resolved in typical images of the beam. Thus clusters effectively add a spatially smooth background signal to the pure diatomic-molecule Rayleigh signal. The main result of the present work is that clustering was not significant. After correcting for interference by small particles imbedded in the T9 flow, cluster scattering was unobservable or smaller than one standard deviation (1-sigma) of the uncertainties for almost all tunnel runs. The total light scattering level was measured to be 1.05 +/- 0.15 (1-sigma) of the expected diatomic scattering, when averaged over the entire usable data set. This result included flow conditions that were supercooled to temperatures of ~ 20 K, about 25 K below the condensation limit of ~ 45 K. Thus the Mach-14 nozzle flow is essentially cluster-free for many supercooled conditions that might be used to extend the facility operating range to larger Reynolds numbers.
Document ID
20190002741
Acquisition Source
Langley Research Center
Document Type
Technical Memorandum (TM)
Authors
Herring, Gregory C. (NASA Langley Research Center Hampton, VA, United States)
Balla, R. Jeffery (NASA Langley Research Center Hampton, VA, United States)
Smith, Michael S. (Arnold Engineering Development Center Silver Spring, MD, United States)
Date Acquired
April 25, 2019
Publication Date
March 1, 2019
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
NF1676L-32466
L-21001
NASA/TM-2019-220259
Funding Number(s)
WBS: WBS 109492.02.07.02.20
Distribution Limits
Public
Copyright
Public Use Permitted.

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