Wingtip Vortex Statistics and Multiscale Evolution in Grid-Generated Turbulent Flow

Freestream turbulence (FST) exerts a pronounced influence on the evolution of wingtip vortices through interactions between multiscale vortex structures. In this study, the vortex statistics and multiscale dynamics of an isolated wingtip vortex subjected to three levels of FST are investigated using time-resolved stereoscopic particle image velocimetry. An ensemble-averaging procedure is employed to obtain the vortex statistics free of vortex wandering motion. The results show that, although the viscous diffusion of the vortex core remains essentially unchanged, increasing FST markedly accelerates the downstream decay of tangential velocity. The primary modifications are confined to the outer region of the vortex. The multiscale velocity fluctuations are further examined using triple decomposition and proper orthogonal decomposition. At large scales, elevated FST intensifies vortex wandering and redistributes the fluctuation energy from a distinct dominant frequency to a broadband spectral response. At smaller scales, the turbulent kinetic energy integrated over the vortex core exhibits a power-law decay with downstream distance, with the decay exponent decreasing substantially as the FST intensity increases. These results elucidate the multiscale response of an isolated wingtip vortex to freestream turbulence and provide new experimental evidence for the distinct roles of FST in modulating large-scale wandering dynamics and small-scale turbulent fluctuations.