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Research Papers: Multiphase Flows

Probing and Imaging of Vapor–Water Mixture Properties Inside Partial/Cloud Cavitating Flows

[+] Author and Article Information
Churui Wan

Department of Engineering Mechanics,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: jsvan@sjtu.edu.cn

Benlong Wang

Department of Engineering Mechanics,
Shanghai Jiao Tong University,
Shanghai 200240, China;
MOE Key Laboratory of Hydrodynamics (SJTU),
Shanghai 200240, China;
Collaborative Innovation Center for Advanced
Ship and Deep-Sea Exploration (CISSE),
Shanghai 200240, China
e-mail: benlongwang@sjtu.edu.cn

Qian Wang

Department of Engineering Mechanics,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: woshidaqianye@126.com

Yongliu Fang

Department of Engineering Mechanics,
Shanghai Jiao Tong University,
Shanghai 200240, China;
MOE Key Laboratory of Hydrodynamics (SJTU),
Shanghai 200240, China
e-mail: ylfang@sjtu.edu.cn

Hua Liu

Department of Engineering Mechanics,
Shanghai Jiao Tong University,
Shanghai 00240, China;
MOE Key Laboratory of Hydrodynamics (SJTU),
Shanghai 200240, China;
Collaborative Innovation Center for Advanced
Ship and Deep-Sea Exploration (CISSE),
Shanghai 200240, China
e-mail: hliu@sjtu.edu.cn

Guoping Zhang

China Ship Scientific Research Center,
Wuxi 214082, China
e-mail: zhanggp_cssrc@163.com

Lianghao Xu

China Ship Scientific Research Center,
Wuxi 214082, China
e-mail: xu_702@163.com

Xiaoxing Peng

China Ship Scientific Research Center,
Wuxi 214082, China
e-mail: henrypxx@163.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 6, 2016; final manuscript received October 6, 2016; published online January 19, 2017. Assoc. Editor: Mark R. Duignan.

J. Fluids Eng 139(3), 031303 (Jan 19, 2017) (10 pages) Paper No: FE-16-1221; doi: 10.1115/1.4035013 History: Received April 06, 2016; Revised October 06, 2016

Experimental results of the void fraction, statistical chord length distribution (CLD), and bubble size distribution (BSD) inside and downstream of hydrodynamic cavities are presented at the laboratory scale. Various cavitating flows have been intensively studied in water tunnels for several decades, but no corresponding quantitative CLD and BSD data were reported. This experimental study is aimed at elaboration of a general approach to measure CLD in typical cavitating flows. Dual-tip electrical impedance probe (dtEIP) is used to measure the void fraction and CLD in different cavitation flows over a flat plate, including both supercavitation and sheet/cloud cavitation. For supercavitating flows, the void fraction of vapor is unity in the major cavity region. In contrast, the maximum void fraction inside the sheet/cloud cavitation region is less than unity in the present studies. The high vapor concentration region is located in the center of the cavity region. Based on the experimental data of CLD, it is found that the mean chord lengths are around 2.9–4.8 mm and 1.9–4.4 mm in the center region and closure region, respectively. The backward converting bubble diameters at the peak of BSD have similar magnitude, with probability density values exceeding 0.2. Empirical parameters of CLD and BSD are obtained for different cavity regions.

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Figures

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Fig. 1

Illustration of the experimental setup: the cavitation tunnel and the plate. We choose a 45 deg wedge with a sharp edge to provide a clean definition of the separation point and leading edge of the cavity.

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Fig. 2

Geometry of the dtEIP. Bottom panels show the microphotographs of the two probe tips.

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Fig. 3

Snapshots of the bubble distributions using a high-speed camera at 400 frames per second; the time lag between two consecutive images is 25 ms

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Fig. 4

Distribution of velocity of various bubbles within one series of measurements. Blue points represent the data of the high-speed camera. For reference, the theoretical terminal velocity of air bubbles in pure water is plotted as a dashed line, and the empirical terminal velocity in tap water is plotted as a solid line [32].

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Fig. 5

Probability distribution of the chord length and diameter. μ=0.47 and σ=0.50. Bar: the directly measured raw data of the chord length; dashed line: normal distribution of the chord length, Pc(c;μ,σ); and solid line: spherical-corrected probability distribution Pp(d) using Eq. (2).

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Fig. 6

Distribution of the pressure and the standard deviation. The saturated pressure Ps is shown as a thick dashed line for reference.

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Fig. 7

Pressure histories at locations #3 to #6: (a) σv = 1.60 and (b) σv = 1.77

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Fig. 8

Instantaneous high-speed camera pictures of fluid structures at different cavitation numbers: (a) σv = 1.54, (b) σv = 1.60, (c) σv = 1.70, and (d) σv = 1.77

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Fig. 9

Averaged gray level of 2000 frames from the high-speed camera video: (a) σ = 1.60 and (b) σ = 1.77

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Fig. 10

Time-averaged distributions of the void fraction α are shown in black lines, inside the cavity region enclosed with a thick line. Cavitation number σv= 1.54, 1.60, 1.70, and 1.77 from top to bottom. The standard deviation of the void fraction is shown as thin lines. The solid and dash lines in green show the thickness of turbulent boundary layer δ defined with fluid properties of liquid phase and vapor phase, respectively.

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Fig. 11

Experimental data of CLD and fitting curves according to the log normal law at the sample positions #3 and #4, corresponding to x = 18 and 24 cm. The vertical coordinate z of the probe is shown in the legend. (a) σv = 1.54, (b) σv = 1.60, and (c) σv = 1.77.

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Fig. 12

Density distribution of the bubble size along the vertical coordinate z in millimeter as indicated in the legends, at four different horizontal sites #1 to #4 along the plate surface corresponding to x= 6 cm, 12 cm, 18 cm, and 24 cm downstream of the separation corner of the plate. The vertical lines in the top of each figure indicate the corresponding mean chord length cM. (a) σv = 1.54, (b) σv = 1.60, and (c) σv = 1.77.

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Fig. 13

Two distinct density distributions of bubble size at the main region of sheet cavitation (a) and the closure region (b). Red asterisks represent experimental data for the supercavitation case σv=1.54, and blue circles and green plus signs are the experimental data for σv=1.60 and 1.77. (a) Solid line is empirical formulation with μ=1.06 and σ=0.67. (b) Dashed line is empirical formulation with μ=0.52 and σ=0.68.

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