Authors: P Bearman A Heyes C Lear D Smith
Publish Date: 2007/08/28
Volume: 43, Issue: 4, Pages: 501-507
Abstract
In this paper results from an experimental study of the natural and forced evolution of a pair of counter rotating wingtip vortices are reported The vortices were generated using a pair of opposed wingtips in a wind tunnel and measurements made up to 77 tipspacings downstream of the models at a chord Reynolds number of 13 × 105 The wake was interrogated using 2D particle image velocimetry and the longwave Crow instability observed Velocity data were recorded throughout the lifetime of the instability from initial growth through linking formation of vortex rings and their subsequent decay Forcing was achieved using pulsed air jets blowing in the spanwise direction from the wing tip and imparting spatially periodic perturbations to the vortices Forcing at a frequency within the range amplified by the Crow instability was found to enhance the instability growth rate whereas forcing at a frequency outside the amplified range was found to inhibit instability growth In the latter case the imparted wavelength was observed to die out with a preferred wavelength growing in its placemass flow coefficient left ifmmodeexpandafterdotelseexpandafterfim j mathordleft/ vphantom ifmmodeexpandafterdotelseexpandafterfim j rho U infty S right kernnulldelimiterspace rho U infty S right
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