Vortex Breakdown in a Swirling Jet with Axial Forcing

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URI: http://hdl.handle.net/2042/15578
Title: Vortex Breakdown in a Swirling Jet with Axial Forcing
Author: OBERLEITHNER, Kilian; PASCHEREIT, Oliver; WYGNANSKI, Israel
Abstract: A swirling jet has been generated in water by passing the fluid through a rotating honeycomb and discharging it into a water tank. Experiments were conducted at 3000 < Re < 7000 and 1.15 < S < 1.5. In addition, axial periodic perturbations were applied in order to excite the shear layer by an axisymmetric mode m=0. The amplitudes of the forcing were in the range 4% < A < 44%. Quantitative measurements were carried out by using STEREO-PIV. Experiments show that at higher Reynolds numbers the vortex breakdown does not occur abruptly as often mentioned in the literature. Instead, all mean quantities which characterize the vortex breakdown show a continuous change with increasing swirl. The high turbulence level may explain the differences to former studies. Velocity contours of the cross-sectional view indicate azimuthal modes that decrease from m=4 close to the nozzle to m=2 near the vortex breakdown. Phase-locked data show that the location of vortex breakdown alternates with the forcing frequency without a significant mean displacement, whereas for a certain combination of frequency and amplitude it sheds downstream while losing its intensity.
Subject: C3 Stratified and rotating flows ; Geostrophic Dynamics-Instabilities; Vortex Breakdown; Turbulence; Swirl
Publisher: AFM, Maison de la Mécanique, 39/41 rue Louis Blanc - 92400 Courbevoie
Date: 2007-08-28

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