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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN:
1-56700-135-1 (Print)

ON VORTEX GENERATING JETS

Zia U. Khan
AT. Kearney, Inc. 153 East 53rd Street, New York NY 10022, USA

James P. Johnston
Department of Mechanical Engineering Stanford University Stanford, CA 94305-3030, USA

Abstract

Vortex Generating Jets (VGJs) are jets that pass through a wall and into a crossflow to create a dominant streamwise vortex that remains embedded in the boundary layer over the wall. The VGJ is characterized by its pitch and skew angles (Φ and Θ), and the velocity ratio between the jet and the crossflow (VR).
The VGJ configuration of Φ=30°, Θ=60° for VR=1.0 has been identified as that which produces the strongest vortex. Three component Laser Doppler Velocimetry (LDV) data for this particular configuration demonstrate many interesting features of the flow. Mean velocity data show a deficit of streamwise momentum in the core of the vortex, thinning of the boundary layer on the downwash side of the vortex, and thickening of the boundary layer on the upwash side. Plots of the turbulent kinetic energy and the turbulent shear stress show that the turbulent structure of the boundary layer is grossly disturbed by the presence of the vortex. The turbulent transport of the turbulent kinetic energy shows the possibility for a gradient diffusion model in most regions but not not the vortex core.