Confined flow vortex breakdown control using a small rotating disk

The steady-state flow generated by a rotating bottom in a closed cylindrical container and the resulting vortex breakdown bubbles have been studied experimentally. By comparing the flow inside two different container geometries, one with a rigid cover and the other with a free surface, we examined the way in which the formation and structure of the breakdown bubbles depend on the surrounding flow. Details of the flow were visualized by means of the electrolytic precipitation technique, whereas a particle tracking technique was used to characterize the whole flow field. We found that the breakdown bubbles inside the container flow are in many ways similar to those in vortex tubes. First, the bubbles are open with in- and outflow and second, their structure is, like in the case of vortex breakdown in pipe flows, highly axisymmetric on the upstream side of the bubble and asymmetric on their rear side. However, and surprisingly, we observed bubbles which are open and stationary at the same time. This shows that open breakdown bubbles are not necessarily the result of periodic oscillations of the recirculation zone. The asymmetry of the flow structure is found to be related to the existence of asymmetric flow separations on the container wall. If the angular velocity of the rotating bottom is increased the evolution of the breakdown bubbles is different in both configurations: in the rigid cover case the breakdown bubbles disappear but persist in the free surface case.

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Dual vortex breakdown in a two-fluid confined flow

Physics of Fluids ◽

10.1063/5.0012156 ◽

2020 ◽

Vol 32 (6) ◽

pp. 061706 ◽

Cited By ~ 1

Author(s):

Igor V. Naumov ◽

Bulat R. Sharifullin ◽

Mikhail A. Tsoy ◽

Vladimir N. Shtern

Keyword(s):

Vortex Breakdown ◽

Confined Flow ◽

Two Fluid

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Vortex Breakdown in an Enclosed Cylinder With a Partially Rotating Bottom-Wall

Journal of Fluids Engineering ◽

10.1115/1.2969427 ◽

2008 ◽

Vol 130 (11) ◽

Author(s):

P. Yu ◽

T. S. Lee ◽

Y. Zeng ◽

H. T. Low

Keyword(s):

Aspect Ratio ◽

Vortex Breakdown ◽

Numerical Study ◽

Axisymmetric Flow ◽

Rotating Disk ◽

Bottom Wall ◽

Cylindrical Chamber ◽

Noticeable Effect ◽

Disk Radius ◽

Boundary Curves

A numerical study of the axisymmetric flow in a cylindrical chamber of height H is presented, which is driven by a bottom disk rotating at angular velocity Ω. However, unlike most previous studies, the present rotating disk is of smaller radius than the bottom-wall. The boundary curves for the onset of vortex breakdown are presented using different definitions of the nondimensional parameters, depending on whether the cylinder radius R or the disk radius rd is used as the length scale. The study shows that the boundary curves are best correlated when presented in terms of the Reynolds number Ωrd2∕υ, aspect ratio H∕R, and cylinder-to-disk ratio R∕rd. The cylinder-to-disk ratio R∕rd up to 1.6 is found to have noticeable effect on vortex breakdown; this is attributed to the change of effective aspect ratio. The contours of streamline, angular momentum, and azimuthal vorticity are presented and compared with those of whole bottom-wall rotation.

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Experimental Characterisation of the Far-Field Noise in Axial Fans Fitted with Shaped Tip End-Plates

ISRN Mechanical Engineering ◽

10.5402/2012/212358 ◽

2012 ◽

Vol 2012 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

S. Bianchi ◽

A. Corsini ◽

A. G. Sheard

Keyword(s):

Vortex Breakdown ◽

Vortex Formation ◽

Broadband Noise ◽

Sound Power ◽

Far Field ◽

Tip Leakage Flow ◽

Noise Sources ◽

End Plate ◽

Field Noise ◽

Flow Vortex

The authors investigate the far-field noise emissions of a datum fan blade fitted with tip end-plate geometries, originally designed to control the leakage vortex swirl level. The end-plate geometries influence the tip-leakage flow, vortex formation, and swirl level. In doing so, the end-plate geometries influence the sound-power levels. After an evaluation of fan rotors' aerodynamic performance, the study compares the rotors' far-field noise signature characterised in terms of sound-power and pressure-level spectra to enable and assess the end-plate acoustic pay-off. The investigation attempts to establish a cause-and-effect relationship between the tip-flow dynamics and the radiated sound fields, exploring the diverse directivity patterns. The authors found a tonal reduction, due to the enhanced blade-tip end-plates and clarified the relevance of the tip features influencing the radial distribution of the noise sources using coherence analysis. The modified multiple-vortex breakdown end-plate design was effective in reducing the broadband noise, giving an improvement in the frequency range of the turbulent noise.

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Velocity Measurements of Vortex Breakdown in an Enclosed Cylinder

Journal of Fluids Engineering ◽

10.1115/1.1385834 ◽

2001 ◽

Vol 123 (3) ◽

pp. 604-611 ◽

Cited By ~ 16

Author(s):

Kazuyuki Fujimura ◽

Hiroaki Yoshizawa ◽

Reima Iwatsu ◽

Hide S. Koyama ◽

Jae Min Hyun

Keyword(s):

Laser Doppler Velocimetry ◽

Vortex Breakdown ◽

Rotating Disk ◽

Velocity Fields ◽

Laser Doppler ◽

Velocity Measurements ◽

Experimental Apparatus ◽

Breakdown Phenomenon ◽

Component Velocity ◽

Flow Visualizations

Experimental measurements were carried out of three-component velocity fields inside a cylindrical container. Flow was driven by the rotation of the top endwall disk. The purpose of the precision laser-Doppler velocimetry measurements was to describe the velocity characteristics pertinent to the vortex breakdown phenomenon. A turntable experimental apparatus was fabricated. Extensive laser-Doppler measurements, as well as flow visualizations, were made for the aspect ratio 1.50 and 2.50, and the Reynolds number ranges 0.99×103-2.20×103. The measured meridional velocities were found to be consistent with the prior visualization studies. The characteristic changes in swirling motions in the vicinity of vortex breakdown bubble are depicted. Detailed flow patterns near the rotating disk are constructed by using the experimental data.

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