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Research Papers: Multiphase Flows

Combined Experimental and Computational Investigation of Unsteady Structure of Sheet/Cloud Cavitation

[+] Author and Article Information
Biao Huang

School of Mechanical and Vechicular Engineering,
Beijing Institute of Technology,
5 South Zhongguancun Street,
Beijing, 100081, China;
Department of Naval Architecture and
Marine Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: huangbiao@bit.edu.cn

Yin L. Young

Department of Naval Architecture and
Marine Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: ylyoung@umich.edu

Guoyu Wang

School of Mechanical and
Vechicular Engineering,
Beijing Institute of Technology,
5 South Zhongguancun Street,
Beijing, 100081, China

Wei Shyy

Department of Mechanical Engineering &
Provost's Office,
The Hong Kong University of
Science and Technology,
Clear Water Bay,
Kowloon, Hong Kong, China
e-mail: weishyy@ust.hk

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 19, 2012; final manuscript received January 16, 2013; published online May 17, 2013. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 135(7), 071301 (May 17, 2013) (16 pages) Paper No: FE-12-1461; doi: 10.1115/1.4023650 History: Received September 19, 2012; Revised January 16, 2013

The objective of this paper is to apply combined experimental and computational modeling to investigate unsteady sheet/cloud cavitating flows. In the numerical simulations, a filter-based density corrected model (FBDCM) is introduced to regulate the turbulent eddy viscosity in both the cavitation regions on the foil and in the wake, which is shown to be critical in accurately capturing the unsteady cavity shedding process, and the corresponding velocity and vorticity dynamics. In the experiments, high-speed video and particle image velocimetry (PIV) technique are used to measure the flow velocity and vorticity fields, as well as cavitation patterns. Results are presented for a Clark-Y hydrofoil fixed at an angle of attack of α = 8 deg at a moderate Reynolds number, Re = 7 × 105, for both subcavitating and sheet/cloud cavitating conditions. The results show that for the unsteady sheet/cloud cavitating case, the formation, breakup, shedding, and collapse of the sheet/cloud cavity lead to substantial increase in turbulent velocity fluctuations in the cavitating region around the foil and in the wake, and significantly modified the wake patterns. The turbulent boundary layer thickness is found to be much thicker, and the turbulent intensities are much higher in the sheet/cloud cavitating case. Compared to the wetted case, the wake region becomes much broader and is directed toward the suction side instead of the pressure side for the sheet/cloud cavitation case. The periodic formation, breakup, shedding, and collapse of the sheet/cloud cavities, and the associated baroclinic and viscoclinic torques, are shown to be important mechanisms for vorticity production and modification.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

(a) Schematic of the cavitation tunnel, and (b) schematic of the experimental setup

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Fig. 2

Sketch of the foil's position in the test section

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Fig. 3

Measured mean velocity and turbulence intensity distributions along the spanwise direction in the test section without the presence of the hydrofoil at U = 10 m/s, σ = 2.00

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Fig. 4

2D boundary conditions and mesh used in the CFD computations

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Fig. 5

(a) Typical flow visualization and schematic interpretation in experiment, and (b) comparisons of the predicted time evolution of the normalized cavity area (based on boundary defined by 10% vapor fraction isoline) with experimental measurements. σ = 0.8, Re = 7 × 105, α = 8 deg.

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Fig. 6

Comparisons of the experimentally observed cavitation pattern (left), numerically predicted vapor fraction contours and flow streamlines (middle) and vorticity contours (right) σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 7

Numerically predicted time evolution of the predicted (a) water vapor fraction (αv) and (b) reverse u-velocity in various sections (the position is reported in ordinate, from the foil leading edge x/L0 = 0 to the trailing edge x/L0 = 1) for σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 8

Comparisons of the predicted vorticity (left) and turbulent eddy viscosity (right) contours obtained using the original k–ε model, and the DCM and FBDCM approaches at 0.625 Tref for σ = 0.8, Re = 7 × 105, and α = 8 deg

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Fig. 10

Comparisons of the measured (Exp) and predicted (Num) mean, mode, and SD of the ensemble averaged axial velocity profiles at selected chordwise locations along the foil for sheet/cloud cavitating flow. σ = 0.8, Re = 7 × 105, α = 8 deg.

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Fig. 9

Comparisons of the measured (Exp) and predicted (Num) mean, mode, and SD of the ensemble averaged axial velocity profiles at selected chordwise locations along the foil for subcavitating flow. σ = 2.0, Re = 7 × 105, α = 8 deg.

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Fig. 11

Comparisons of the measured and predicted normalized ensemble averaged amplitudes of the turbulent velocity fluctuations at the selected monitoring locations along the foil for σ = 2.0 and σ = 0.8 at Re = 7 × 105, α = 8 deg

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Fig. 12

Comparisons of the measured and predicted normalized averaged z-vortity, ωz/ωo profiles at the selected monitoring locations along the foil for σ = 2.0 and σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 13

Comparisons of the predicted baroclinic torque (left) and vorticity transport/stretching term (middle) in Eq. (12), and the corresponding ratio of baroclinic torque to the vorticity transport/stretching term (right) obtained using (a) the original k–ε model, (b) the DCM model, and (c) the FBDCM model at 0.625 Tref for σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 14

Comparison of the predicted baroclinic torque (left), vorticity transport/stretching term (middle) and the ratio of the baroclinic torque to the vorticity/stretching term (right) in Eq. (12) at selected times obtained using the FBDCM model. σ = 0.8, Re = 7 × 105, α = 8 deg.

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Fig. 15

Schematic of the configuration used for PIV measurements in the wake of a cavitating hydrofoil. Field of view is 80 mm × 55 mm, and is illuminated by Nd: YAG laser.

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Fig. 16

Measured normalized ensemble averaged axial velocity contours in the wake region at (a) σ = 2.0 and (b) σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 17

Comparisons of the measured (Exp) and predicted (Num) normalized ensemble averaged axial velocity profiles at the selected monitoring locations in the wake region for σ = 2.0 and σ = 0.8 at Re = 7 × 105, α = 8 deg

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Fig. 18

Measured normalized amplitude of the turbulent velocity fluctuations in the wake region at (a) σ = 2.0 and (b) σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 19

Comparisons of the measured (Exp) and predicted (Num) normalized fluctuating velocity profiles at the selected monitoring locations in the wake region for σ = 2.0 and σ = 0.8, Re = 7 × 105, α = 8 deg

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Fig. 20

Comparisons of the measured (Exp) and predicted (Num) normalized ensemble averaged z-vorticity, ωz/ωo, profiles at the selected monitoring locations in the wake region for σ = 2.0 and σ = 0.8, Re = 7 × 105, α = 8 deg

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