Research Papers: Multiphase Flows

Measurements in High Void-Fraction Bubbly Wakes Created by Ventilated Supercavitation

[+] Author and Article Information
Martin Wosnik

Department of Mechanical Engineering,
University of New Hampshire,
S252 Kingsbury Hall,
33 Academic Way,
Durham, NH 03824
e-mail: martin.wosnik@unh.edu

Roger E. A. Arndt

St. Anthony Falls Laboratory,
University of Minnesota,
2 Third Avenue S.E.,
Minneapolis, MN 55405
e-mail: arndt001@umn.edu

Manuscript received May 7, 2012; final manuscript received December 11, 2012; published online January 18, 2013. Assoc. Editor: Pavlos P. Vlachos.

J. Fluids Eng 135(1), 011304 (Jan 18, 2013) (9 pages) Paper No: FE-12-1230; doi: 10.1115/1.4023193 History: Received May 07, 2012; Revised December 11, 2012

A study of ventilated supercavitation in the reentrant jet regime has been carried out in the high-speed water tunnel at St. Anthony Falls Laboratory as the hydrodynamics part of an interdisciplinary study on stability and control of high-speed cavity-running bodies. The work is aimed at understanding the interaction between a ventilated supercavity and its turbulent bubbly wake, with the goal to provide the information needed for the development of control algorithms. Particle image velocimetry (PIV) measurements in high-void fraction bubbly wakes created by the collapse of ventilated supercavities are reported. Bubble velocity fields are obtained and are shown to submit to the same high Reynolds number similarity scaling as the single-phase turbulent axisymmetric wake. A grayscale technique to measure local average void fraction is outlined. Results of a time-resolved PIV experiment at 2000 Hz, using an adaptive masking scheme based on a sliding intensity threshold filter, are also presented.

Copyright © 2013 by ASME
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Fig. 6

PIV in the bubbly wake of a ventilated axisymmetric supercavity

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Fig. 7

PIV measurement positions in bubbly wake

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Fig. 4

(a) Ventilated cavitation: air entrainment coefficient Q¯ is increasing top to bottom; cavitation number σc is decreasing top to bottom. (b) Digital cavity images corresponding to measurements of ventilation air demand (cavitator disk diameter d = 10 mm, elliptical strut).

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Fig. 3

Vertical and horizontal cross sections of test body; sharp-edged disk cavitator on left (d = 10 mm)

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Fig. 2

Schematic of high-speed water tunnel

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Fig. 1

Schematic of axisymmetric supercavity

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Fig. 8

Detail of typical PIV image in the bubbly wake of a ventilated axisymmetric supercavity

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Fig. 9

Schematic of axisymmetric wake

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Fig. 10

Local Reynolds number variation with downstream position (here: U0=U∞-UCL, δ is wake width defined as an integral length scale similar to displacement thickness, and θ is momentum thickness (Red = 1.0 × 105))

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Fig. 11

Local turbulence intensity variation in wake

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Fig. 12

Raw velocity data in single-phase liquid wake

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Fig. 13

Velocity data in single-phase liquid wake with high (infinite) Reynolds number scaling (d = 15 mm, U = 6.6 m/s, Red = 1.0 × 105)

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Fig. 14

PIV in the bubbly wake of a ventilated axisymmetric supercavity

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Fig. 16

Local average void fraction in the bubbly wake of a ventilated axisymmetric supercavity (d = 15 mm, Q = 16 l/min, 7 < x/d < 13, σ = 0.2, U = 6.6 m/s, Fr = 17)

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Fig. 17

Local average void fraction in the bubbly wake of a ventilated axisymmetric supercavity (d = 10 mm, Q = 9.8 l/min, 14 < x/d < 34, σ = 0.13, U = 9.1 m/s, Fr = 29)

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Fig. 18

Configuration for time-resolved PIV measurements of bubbly wake of ventilated supercavity

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Fig. 19

PIV image acquired in wake of ventilated supercavity (image from laser 1, 1024 × 512 pixel, cf. Fig. 14). Image was brightened for presentation.

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Fig. 20

Adaptive processing mask obtained from thresholding 32 × 32-pixel areas based on the sum of the grayscale intensity values (here: threshold 127 or normalized 0.5). Overlaid in “active” areas of the mask is the original raw PIV image.

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Fig. 21

(a) Velocity vectors and contours in bubbly wake of ventilated supercavity, σ ≈ 0.14, from cross-correlation of bubbles (missing vectors interpolated, data smoothed with Gaussian filter, vector field matrix multiplied with mask of Fig. 16, wake velocity U = 5.7 m/s subtracted). (b) Velocity vectors and vorticity contours in bubbly wake of ventilated supercavity (parameters are the same as for Fig. 21(a)).

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Fig. 15

PIV in the bubbly wake of a ventilated axisymmetric supercavity (d = 15 mm, Q = 16 l/min, 7 < x/d < 13, σ = 0.2, U = 6.6 m/s, Fr = 17, Red = 1.0 × 105)




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