An experimental investigation of wing-tip vortex decay in turbulence

Abstract

Particle image velocimetry measurements were conducted for a wing-tip vortex decaying in free-stream turbulence. The vortex exhibited stochastic collapse with free-stream turbulence present, with the breakdown initiating earlier for higher levels of turbulence. An increased rate of decay of the vortex tangential velocity was also observed, increasing with increasing free-stream turbulence. The decay of the vortex tangential velocity without the free-stream turbulence was well represented by viscous diffusion, resulting in an increase in the core radius and decrease in the peak tangential velocity. With the addition of free-stream turbulence, the rate of decay of the peak tangential velocity of the vortex increases, whereas the rate of increase of core radius remains unchanged. The circulation of the vortex decayed in time when immersed in free-stream turbulence, whereas it remained approximately constant when free-stream turbulence was not present. This decay in circulation was found to be almost entirely due to a decrease in circulation of the vortex core, caused by the relative decrease in the peak tangential velocity without a corresponding increase in the core radius. The scaling of the radial profiles of velocity and circulation was also examined, and it was found that, regardless of the free-stream condition, the core was scaled by the peak tangential velocity and core radius. The region outside the core did not scale with these quantities, and an alternative scaling for circulation is proposed which results in improved collapse of the profiles.