Long-wavelength vortex motion induced by free-stream turbulence

This study further examines experimentally the motion of an isolated vortex immersed in grid-generated free-stream turbulence. Using a novel analytical procedure, we determined approximately the time history of the vortex axis position from velocity vectors at two locations measured simultaneously with the use of hot-wire anemometry. We identified a long-wavelength, organized, helical motion of the vortex axis, which is present in both low-turbulence and high-turbulence streams, thus pointing to a universal instability mechanism. Free-stream turbulence appears to intensify this instability, while simultaneously enhancing the stochastic motion of the vortex axis.