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Research Papers

Experimental Investigation of Cavitation Behind a Circular Cylinder in Cross-Flow

[+] Author and Article Information
Pankaj Kumar

Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: pankaj20221@gmail.com

Shamit Bakshi

Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: shamit@iitm.ac.in

Dhiman Chatterjee

Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: dhiman@iitm.ac.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received May 19, 2016; final manuscript received September 10, 2016; published online April 4, 2017. Assoc. Editor: Ziad Saghir.

J. Thermal Sci. Eng. Appl 9(3), 031004 (Apr 04, 2017) (6 pages) Paper No: TSEA-16-1135; doi: 10.1115/1.4035923 History: Received May 19, 2016; Revised September 10, 2016

Cavitation behind a circular cylinder is studied with the aid of highly time-resolved images at a constant Reynolds number of 64,000. Apart from recording the overall cavitation activity behind the cylinder, the study also delves into the dynamics of individual cavities. The length of cavity scales with cavitation number and this scaling is similar to the existing results obtained in flow regimes different from that presented here. Dynamics of individual cavities show distinct phases of cavity formation, growth, and collapse. At lower cavitation numbers, cavity collapse was followed by a rebounce. Variation of area normalized by the length of cavity shows self similarity in the growth phase of cavities for different cavitation numbers. Thus, the cavity length is the suitable length scale for dynamics of cavities, at least for the growth phase. The cavity lifetime scales inversely with the square of cavitation number. Dynamics of individual small cavity captured at higher frame rates was found to be similar to that of an isolated bubble. In this case, a rapid collapse follow a more gradual expansion phase, unlike that shown by larger cavities.

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Figures

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Fig. 1

Schematic of the test section along with instrumentation

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Fig. 2

Coefficient of pressure (CP) with angular position (θ): (a) σ/σi=1.2 to 0.68 and (b) σ/σi=0.68 to 0.50

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Fig. 3

Variation of drag coefficient (CD) and base pressure coefficient (CPb) with cavitation number

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Fig. 4

Snapshot of the bottom view of cavitating wake indicative of the extent of cavity at different cavitation number: (a) σ/σi=0.85, (b) σ/σi=0.80, (c) σ/σi=0.68, (d) σ/σi=0.58, (e) σ/σi=0.54, and (f) σ/σi=0.50. Flow is from right to left. Images were captured at 1000 frames/s.

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Fig. 5

Image processing steps to determine the length of cavity: (a) instantaneous gray-scale image, (b) mean black and white image, and (c) intensity variation along streamwise direction. Dashed circle in (a) and (b) indicates that the cylinder while dashed vertical lines in (b) show the location used for determination of the length of cavity for σ/σi=0.5. Flow is from right to left in (a) and (b).

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Fig. 6

Variation of normalized length (Lc/D) with cavitation number

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Fig. 7

Occurrence of cavity behind the cylinder near inception (σ/σi = 0.85). The image was captured at 3600 frames/s. Flow is from right to left.

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Fig. 8

Sequence of images depicting the life of a cavity from its initiation to growth and complete collapse at σ/σi = 0.50: (a) initiation, (b) growth, (c) coalescence, (d) maximum size, (e) convects downstream, (f) intermediate stage of collapse, (g) collapse, (h) rebounce, and (i) complete collapse. Flow is from right to left. Images were captured at 3600 frames/s.

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Fig. 9

Variation of cavity area and cavity position with time for a typical cycle at σ/σi=0.5. Points (a)–(i) correspond to the sequence of images shown in Fig. 8. tL represents the total cavity life.

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Fig. 10

(a) Variation of cavity area with time. t refers to time spent from the formation of the cavity. (b) Cavity area normalized with cavity length (LC) and plotted against time. Cavity length (LC) is obtained from Fig. 6 where lower cavitation number (σ/σi=0.58, 0.54, and 0.5) is obtained from our experiment and higher cavitation number (σ/σi=0.85, 0.8, and 0.68) is obtained from correlation developed by Varga and Sebestyen [4] and shown in Fig. 6.

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Fig. 11

Nondimensional cavity life time (τ=(tLD/U)) variation with cavitation number

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Fig. 12

Single cavity formation, collapse, and rebounce in cycle for σ/σi=0.5. Flow is from right to left. High speed images were taken at 20,000 frames/s. Image sequence is shown in every 0.15 ms intervals.

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Fig. 13

Dynamics of single cavity shown in Fig. 12: growth, collapse, and rebounce

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