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Research Papers: Multiphase Flows

Numerical Investigations of Pressure Distribution Inside a Ventilated Supercavity

[+] Author and Article Information
Lei Cao

Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China;
Saint Anthony Falls Laboratory,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55414

Ashish Karn

Department of Mechanical Engineering,
College of Engineering Roorkee,
Roorkee 247667, Uttarakhand, India

Roger E. A. Arndt

Saint Anthony Falls Laboratory,
University of Minnesota,
Minneapolis, MN 55414

Zhengwei Wang

Department of Thermal Engineering,
Tsinghua University,
Beijing 100084, China

Jiarong Hong

Saint Anthony Falls Laboratory,
Department of Mechanical Engineering,
University of Minnesota,
Minneapolis, MN 55414
e-mail: jhong@umn.edu

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received October 29, 2015; final manuscript received October 10, 2016; published online December 7, 2016. Assoc. Editor: Satoshi Watanabe.

J. Fluids Eng 139(2), 021301 (Dec 07, 2016) (8 pages) Paper No: FE-15-1786; doi: 10.1115/1.4035027 History: Received October 29, 2015; Revised October 10, 2016

A numerical study has been conducted on the internal pressure distribution of a ventilated supercavity generated from a backward facing cavitator under different air entrainment coefficients, Froude numbers, and blockage ratios. An Eulerian multiphase model with a free surface model is employed and validated by the experiments conducted at St. Anthony Falls Laboratory of the University of Minnesota. The results show that the internal pressure in the major portion of the supercavity is primarily governed by the hydrostatic pressure of water, while a steep adverse pressure gradient occurs at the closure region. Increasing the air entrainment coefficient does not largely change the pressure distribution, while the cavity tail extends longer and consequently the pressure gradient near the closure decreases. At smaller Froude number, there is a more pronounced gravitational effect on the supercavity with increasing uplift of the lower surface of the cavity and a decreasing uniformity of the pressure distribution in the supercavity. With the increase of blockage ratio, the overall pressure within the supercavity decreases as well as the pressure gradient in the main portion of the supercavity. The current study shows that the assumption of uniform pressure distribution in ventilated supercavities is not always valid, especially at low Fr. However, an alternative definition of cavitation number in such cases remains to be defined and experimentally ascertained in future investigations.

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References

Figures

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Fig. 1

(a) A side view of the test section and the mounting configuration of the backward facing cavitator, (b) a sectional view, and (c) a close-up view of the cavitator, ventilation line and the hypodermic tube used for pressure measurement. The dimensions shown in the figure are in centimeters. Adapted from Ref. [7].

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Fig. 2

Three-dimensional geometry of the computational domain (in this figure dc = 20 mm)

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Fig. 3

Partial view of the grid on the symmetry plane

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Fig. 4

Comparison of experimental and numerical results (a) photograph of ventilated cavity from experiment, (b) numerical air volume fraction distribution on the symmetry plane, and (c) numerical isosurface of rair = 0.5

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Fig. 5

Profiles of the three cavities with different air entrainment coefficients

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Fig. 6

Pressure coefficient distribution on the symmetry plane with different air entrainment coefficients (a) CQs = 0.10, (b) CQs = 0.15, and (c) CQs = 0.20

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Fig. 7

Streamlines of the air flow inside the supercavity (CQs = 0.15)

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Fig. 8

Twin vortices at the closure with different air entrainment coefficients (a) CQs = 0.10, (b) CQs = 0.15, and (c) CQs = 0.20

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Fig. 9

Profiles of the three cavities with different Froude numbers

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Fig. 10

Pressure coefficient distribution on the symmetry plane for different Froude numbers (a) Fr = 9, (b) Fr = 18, and (c) Fr = 27

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Fig. 11

Profiles of three cavities with different blockage ratios (a) original shape and (b) normalized shape

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Fig. 12

Pressure coefficient distribution on the symmetry plane for different blockage ratios (a) B = 5%, (b) B = 9%, and (c) B = 14%

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