Measurements of a turbulent vortex pair using time resolved PIV

Stereoscopic time resolved PIV is applied to study vortex pair instabilities. The two vortices are generated by a split wing apparatus that is designed to fasten the development of cooperative instabilities such as the Crow and Widnall modes thanks to a short vortex separation and a strong circulation. We use spectral analysis and vortex center detection to validate the presence of both instabilities. In addition we characterize these instabilities in terms of wevelength, growth rate and of the direction of the oscillations of the vortices. Our results are found to be in good agreement with theoretical results taken from litterature. The structure of the flow is found to be richer than the sole instabilities, with the presence of strong turbulence levels at the outskirts of the vortices, that results from the elongation of vorticity at the leading stagnation point of the vortex pair and wrapping of this vorticity around the vortex cores.