The behaviour of horse-shoe like vortices (H-S vortices), which appear on the surfaces of spiral vortices in the laminar boundary-layer of a rotating cone, are experimentally investigated in detail using a drum camera and a light sheet illumination system with a stroboscope flash light. With this method, the time dependent turbulent transition processes of these H-S vortices are greatly clarified. The results show that the H-S vortices, which are traveling along the spiral vortices with certain phase velocity, are generated by steep shear velocity profiles with an inflexion point which is created by the existence of the spiral vortices. This work is pertinent to heat transfer and aerodynamics.
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