An Experimental Investigation of Vortex Breakdown in Tubes at High Reynolds Numbers

An Experimental Investigation of Vortex Breakdown in Tubes at High Reynolds Numbers
Author: Francis G. Novak
Publisher:
Total Pages: 336
Release: 1998-09-01
Genre:
ISBN: 9781423557371

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This thesis deals with non-cavitating swirling flows with vortex breakdown in various tubes. Phenomenological and quantitative investigations were carried out at Reynolds numbers as high as 300,000. It was shown that a high Re(D) vortex transitions to its new state (breaks down) via a rapidly spinning spiral form, as demonstrated with 4,000 frame per second video, short exposure time (6 ns) imaging, and Digital Particle Image Velocimetry. Of the known types, the spiral emerges as the fundamental breakdown form and the axisymmetric bubble may now be regarded as a relatively low Re(D) occurrence that is bypassed at sufficiently high Re(D). Some new phenomena were observed at high Re(D): Extremely rapid spiral rotation (over 1,000 revolutions per second), core bifurcation, and changes in the sense of the spiral windings. Familiar features of breakdowns, such as the transition from a jet-like to wake-like axial velocity profile and the rapidly expanding vortex core, were observed in extensive time averaged velocity and turbulence results ascertained with Laser Doppler Velocimetry. However, a mean stagnation point and recirculation were absent in the highest Re(D) flow. The core meandering and stagnation point darting in the turbulent flow field were quantified and discussed in detail.

An Experimental Investigation of the Vortex-breakdown Phenomenon

An Experimental Investigation of the Vortex-breakdown Phenomenon
Author: Turgut Sarpkaya
Publisher:
Total Pages: 0
Release: 1970
Genre: Vortex-motion
ISBN:

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The results of an experimental investigation of the characteristics of stationary and travelling vortex breakdowns in swirling flow in a diverging cylindrical tube are presented and discussed. Basically, three types of vortex breakdown were observed, viz., double helix, spiral, and axisymmetric breakdown. The type and location of the stationary breakdowns were found to be dependent upon the Reynolds and circulation numbers of the flow. The breakdown bubble responded to gradual and abrupt changes in the upstream and downstream flow conditions in a manner analogous to the hydraulic jump in open-channel flow. The observations reported and the evidence presented revealed unmistakably that the vortex breakdown is a finite transition from a uniform state of swirling flow (supercritical) to one (subcritical) featuring a large standing wave, followed by standing wavelets, of finite amplitude. (Author).

An Experimental Investigation of the Effect of Adverse Pressure Gradient on Vortex Breakdown

An Experimental Investigation of the Effect of Adverse Pressure Gradient on Vortex Breakdown
Author: Gale Edward Treiber
Publisher:
Total Pages: 74
Release: 1973
Genre: Mechanical engineering
ISBN:

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The results of an experimental investigation of the effect of adverse pressure gradient on the vortex breakdown phenomenon in a diverging tube are presented. Adverse pressure gradient was found to be as significant in determining the breakdown position as were the previously known parameters of Reynolds and circulation numbers. An approximate momentum analysis for predicting the vortex breakdown position was carried out which appears to hold promise as a breakdown predictor. (Modified author abstract).

Streamwise Fluctuations of Vortex Breakdown at High Reynolds Numbers

Streamwise Fluctuations of Vortex Breakdown at High Reynolds Numbers
Author:
Publisher:
Total Pages: 49
Release: 2006
Genre: Stagnation point
ISBN:

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This thesis deals with the characterization of the dependence on the flow geometry of the stream wise fluctuations of the stagnation point of vortex breakdown in axisymmetric tubes and over delta wing aircraft. The statistical analysis presented herein shows that in an axisymmetric tube the 'darting' about the mean stagnation point are distributed normally for the two Reynolds numbers: Re(D) 230,000 and 300,000 (independently of the Reynolds number in the range noted). The darting over a delta wing is not only non-Gaussian but also exhibits rather large localized fluctuations (Stouhal numbers ranging from 0.04 to 0.1). presumably due to the strong influence of the surrounding flow and the geometrical conditions: increase of circulation along the trailing edge, the abrupt separation of flow at the base of the delta wing, and other protuberances that emerge from the upper and lower surfaces of the wing (support elements in laboratory and stabilizers on delta wing aircraft). It is concluded that the behavior of vortex breakdown is strongly dependent on the surrounding geometry and that only experiments in axisymmetric tubes can provide the purest form of vortex breakdown for numerical simulations and analytical studies towards the understanding of the internal turbulence and its spectrum within the breakdown bubble for theoretical and industrial purposes.