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Water-tunnel experiments on an oscillating airfoil at RE equals 21,000Flow visualization experiments were performed in a water tunnel on a modified NACA 0012 airfoil undergoing large amplitude harmonic oscillations in pitch. Hydrogen bubbles were used to: (1) create a conveniently striated and well preserved set of inviscid flow markers; and (2) to expose the succession of events occurring within the viscous domain during the onset of dynamic stall. Unsteady effects were shown to have an important influence on the progression of flow reversal along the airfoil surface prior to stall. A region of reversed flow underlying a free shear layer was found to momentarily exist over the entire upper surface without any appreciable disturbance of the viscous-inviscid boundary. A flow protuberance was observed to develop near the leading edge, while minor vortices evolve from an expanding instability of the free shear layer over the rear portion of the airfoil. The complete breakdown of this shear layer culminates in the successive formation of two dominant vortices.
Document ID
19780011115
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Mcalister, K. W. (NASA Ames Research Center Moffett Field, CA, United States)
Carr, L. W. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 3, 2013
Publication Date
March 1, 1978
Subject Category
Aerodynamics
Report/Patent Number
NASA-TM-78446
A-7232
Accession Number
78N19058
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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