Growth of Vortical Structures by Interaction between Horizontally Displaced Horseshoe Vortices in a Turbulent Boundary Layer

Abstract

Interaction phenomena between adjacent two horseshoe vortices were experimentally investigated. A pair of horseshoe vortices was artificially induced by injecting small swirling jets into the bottom of a fully developed turbulent boundary layer. Coherent velocity vector were obtained from the ensemble-averaged velocity components measured through the conditional sampling. When two horseshoe vortices developed downstream, they merged with each other. Merged horseshoe vortices generated M shaped structure and, finally, conformed a single larger horseshoe vortex. As these structures were stretched downstream, ejection and sweep were lined up along the symmetry plane of merged structure. In the lower boundary layer, high and low speed structures were aligned alternately in the spanwise direction.