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Research Papers: Multiphase Flows

Tip Vortex Cavitation Suppression by Active Mass Injection

[+] Author and Article Information
Natasha Chang

Naval Surface Warfare Center - Carderock Division, 9500 MacArthur Blvd., West Bethesda, MD 20817 e-mail: Natasha.chang@navy.mil

Harish Ganesh

 University of Michigan, 2010, Walter E Lay Auto Lab, 1231 Beal Avenue, Ann Arbor, MI, 48109 e-mail: gharish@umich.edu

Ryo Yakushiji

2010, Walter E Lay Auto Lab, 1231 Beal Avenue, Ann Arbor, MI 48109 e-mail: ryaku@muc.biglobe.ne.jp

Steven L Ceccio

 University of Michigan, 215 NAME Bldg., 2600 Draper Dr., Ann Arbor, MI 48109-2133 e-mail: ceccio@umich.edu

J. Fluids Eng 133(11), 111301 (Oct 27, 2011) (11 pages) doi:10.1115/1.4005138 History: Received December 24, 2010; Revised September 07, 2011; Published October 27, 2011; Online October 27, 2011

Injection of water and aqueous polymer solutions in to the core of a trailing vortex was found to delay the inception of tip vortex cavitation (TVC). Optimal levels of mass injection reduced the inception cavitation number from 3.5 to 1.9, or a reduction of 45%. At the optimal fluxes, injection of water alone produced a reduction of 35%, and the addition of polymer solution led to a reduction of 45%. Stereo particle image velocimetry was employed to examine the flow fields in the region of TVC inception and infer the average core pressure, and planar PIV was used to examine the flow unsteadiness in this region. The time-averaged pressure coefficients for the vortex core pressure were estimated and compared to the pressure needed for TVC inception and full development. Measurement of flow variability in the TVC inception region indicated that relatively low fluxes of mass injection in the TVC roll-up region led to a substantial decrease in flow unsteadiness in the core region near the observed location of inception, and this corresponded to a substantial decrease in the inception pressure. Increased injection of water or polymer solutions led to a modest increase in the average vortex core radius, which was discernable in the measured pressure needed for developed cavitation.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) A schematic diagram showing the hydrofoil in the water tunnel test section and the mass injection delivery system. The dimensions are in mm (c refers to the chord length); (b) a drawing of the of the hydrofoil plan and cross section with an image of the Dinj = 1.6 injection hole.

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Figure 2

A schematic diagram of the stereo and planar particle imaging velocimetry (PIV) systems used in the experiment. For stereo PIV, the light sheet was oriented perpendicular to the main flow direction and placed a distance z/c downstream from the tip of the hydrofoil in the region of inception. For the planar PIV, the light sheet was oriented parallel to the main flow direction, and placed to nearly intersect the axis of the forming tip vortex in the region of inception.

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Figure 3

The measured free-stream nuclei spectrum for varying free-stream dissolved oxygen levels and concentrations polymer: (□) water at 70% dissolved oxygen (DO); (⊳) water at 25% DO; (Δ) polymer ocean at 70% DO and 31 wppm PEO; and (+) polymer ocean at 70% DO and 125 wppm PEO.

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Figure 4

(a) The inception cavitation number, σI , and (b) the developed cavitation number, σD , as a function of the injectant volume flow-rate Q with varying polymer fluxes F; (○) F = 0; (▴) F = 4; (▾) F = 16; the solid lines are for cases with the smaller injection port (higher U), and the dashed lines are for the larger injection port (smaller U).

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Figure 5

The event rates and location of incipient TVC bubbles measured for varying injection rates and polymer fluxes. The location of inception is ∼ 0.2 z/c. However, some nuclei were captured by the vortex and incepted at a location z/c > 0.5 for all conditions, and there were some cases of TVC inception due to the introduction of bubbles through the injector. * 1 event or less.

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Figure 6

The averaged in-plane (a) and out-of-plane (b) velocity field at z/c = 0.25 for Q = 0, U = 0, F = 0, the baseline conditions.

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Figure 7

The measured core size, circulation, and inferred core pressure for the baseline and three conditions of polymer injection; cinj  = 500 wppm with U∞  = 8 m/s and Dinj  = 1.6 mm.

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Figure 8

(a) σI  + 〈Cp , Core 〉, and (b) σD  + 〈Cp , Core 〉, as a function of the injectant volume flow-rate Q with varying polymer fluxes F; (○) F = 0; (▴) F = 4; (▾) F = 16; the solid lines are for cases with the smaller injection port (higher U), and the dashed lines are for the larger injection port (smaller U).

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Figure 9

σI - σD as a function of the injectant volume flow-rate Q with varying polymer fluxes F; (○) F = 0; (▴) F = 4; (▾) F = 16; the solid lines are for cases with the smaller injection port (higher U), and the dashed lines are for the larger injection port (smaller U).

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Figure 10

The averaged in-plane velocity fields, 〈vy /U∞ 〉, for the planar cut nearly parallel to the vortex axis for (a) the baseline condition Q = 0, F = 0, U = 0; (b) Q = 0.13, F = 0, U = 0.70; (c) Q = 0.03, F = 16, U = 0.17; and (d) Q = 0.13, F = 16, U = 0.70.

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Figure 11

The RMS in-plane velocity fluctuations, vy ’ /U∞ , for the planar cut nearly parallel to the vortex axis for (a) the baseline condition Q = 0, F = 0, U = 0; (b) Q = 0.13, F = 0, U = 0.70; (c) Q = 0.03, F = 16, U = 0.17; and (d) Q = 0.13, F = 16, U = 0.70.

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Figure 12

The RMS in-plane velocity fluctuations, vy ’ /U∞ , along the vortex axis (a) and perpendicular to the vortex axis (b) with the origin at the location of the maximum fluctuation magnitude; (▪) Q = 0, F = 0, U = 0 (baseline); (○) Q = 0.13, F = 0, U = 0.70; (▴) Q = 0.13, F = 4, U = 0.17; (▾) Q = 0.13, F = 16, U = 0.70; and (♦) Q = 0.03, F = 16, U = 0.70.

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