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HORSEHOE VORTICES IN UNIFORMLY SHEARED TURBULENCE

Christina Vanderwel
Department of Mechanical Engineering University of Ottawa, Canada

Stavros Tavoularis
Department of Mechanical Engineering, University of Ottawa, Ottawa, Ontario KIN 6N5, Canada

Аннотация

Uniformly sheared flow (USF) with a turbulence Reynolds number Reλ of approximately 150 and a shear rate parameter of approximately 12 has been generated in a water tunnel and its instantaneous structure has been examined using flow visualization, laser Doppler velocimetry and particle image velocimetry. Horseshoe-shaped vortices, similar to those observed in turbulent boundary layers (TBL), were found to be prevalent in this flow. These vortices were observed within relatively strong shear layers, which separated regions of fluid with nearly uniform velocity. Like TBL, USF was found to contain structures whose heads pointed towards the high speeds, but, in contrast to TBL, USF also contained inverted structures. These results demonstrate that organized horseshoe/hairpin-type vortices are generated by mean shear irrespectively of the presence of solid walls.