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Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Free FlightSmooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.
Document ID
20100021400
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Reda, Daniel C. (NASA Ames Research Center Moffett Field, CA, United States)
Wilder, Michael C. (NASA Ames Research Center Moffett Field, CA, United States)
Prabhu, Dinesh K. (Eloret Corp. Sunnyvale, CA, United States)
Date Acquired
August 24, 2013
Publication Date
January 4, 2010
Subject Category
Aircraft Design, Testing And Performance
Report/Patent Number
ARC-E-DAA-TN1036
AIAA Paper 2010-1367
Meeting Information
Meeting: 48th AIAA Aerospace Sciences Meeting
Location: Orlando, FL
Country: United States
Start Date: January 4, 2010
End Date: January 7, 2010
Funding Number(s)
CONTRACT_GRANT: NNA04BC25C
Distribution Limits
Public
Copyright
Public Use Permitted.

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