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The Convection Speed of the Dynamic Stall Vortex
Final rept. 1 Nov 1989-31 Oct 1991
GLASGOW UNIV (UNITED KINGDOM) DEPT OF AEROSPACE ENGINEERING
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This report describes measurements of the convection speed of the dynamic stall vortex. A survey reveals a disharmony between the various researchers as to the dependency of the convection speed upon the aerofoil motion. A preliminary analysis of pressure data from aerofoil models tested at Reynolds and Mach numbers of 1.5 million and 0.11 respectively showed that the convection speed was independent of aerofoil motion and model type to a first order. Testing a high aspect ratio NACA 0015 showed that wind tunnel constraint was not a significant factor. An enhanced analysis technique produced results which, in spite of their poor accuracy, suggest that at low pitch rates the convection speed falls with increasing reduced pitch rate to a constant value for the NACA 0015 and 0018 models. The effect of a leading edge trip was to significantly alter the details of the dynamic stall and to change the vortex convection speed. Although the convection speedaerofoil motion dependency anomaly has not been not fully solved, it is suggested that leading edge effects influence the convection speed, and the aerofoil leading edge geometry, Reynolds and Mach numbers are highlighted.
APPROVED FOR PUBLIC RELEASE