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Research Papers: Multiphase Flows

The Influence of Viscous Effects and Physical Scale on Cavitation Tunnel Contraction Performance

[+] Author and Article Information
P. A. Brandner

Australian Maritime Hydrodynamics Research Centre, Australian Maritime College, University of Tasmania, Locked Bag 1395, Launceston, Tasmania 7250, Australia

J. L. Roberts

Tasmanian Partnership for Advanced Computing, University of Tasmania, Private Bag 37, Hobart, Tasmania 7001, Australia

G. J. Walker

School of Engineering, University of Tasmania, Private Bag 65, Hobart, Tasmania 7001, Australia

The AMHRC is a collaborative venture involving the Australian Maritime College (AMC), the Australian Defence Science and Technology Organisation (DSTO), and the University of Tasmania (UTAS).

J. Fluids Eng 130(10), 101301 (Sep 04, 2008) (14 pages) doi:10.1115/1.2969274 History: Received May 15, 2007; Revised July 03, 2008; Published September 04, 2008

The general performance of an asymmetric cavitation tunnel contraction is investigated using computational fluid dynamics (CFD) including the effects of fluid viscosity and physical scale. The horizontal and vertical profiles of the contraction geometry were chosen from a family of four-term sixth-order polynomials based on results from a CFD analysis and a consideration of the wall curvature distribution and its anticipated influence on boundary layer behavior. Inviscid and viscous CFD analyses were performed. The viscous predictions were validated against boundary layer measurements on existing full-scale cavitation tunnel test section ceiling and floor and for the chosen contraction geometry against model-scale wind tunnel tests. The viscous analysis showed the displacement effect of boundary layers to have a fairing effect on the contraction profile that reduced the magnitude of local pressure extrema at the entrance and exit. The maximum pressure gradients and minimum achievable test section cavitation numbers predicted by the viscous analysis are correspondingly less than those predicted by the inviscid analysis. The prediction of cavitation onset is discussed in detail. The minimum cavitation number is shown to be a function of the Froude number based on the test section velocity and height that incorporate the effects of physical scale on cavitation tunnel performance.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 5

Viscous CFD grid independence test for various values of IBT

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Figure 6

Measured test section floor/ceiling boundary layer profiles at x=0.12

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Figure 7

Comparison of measured and predicted test section ceiling/floor centerline boundary layer displacement and momentum thicknesses at x=0.12

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Figure 8

Boundary element mesh for inviscid CFD analysis with 7744 elements

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Figure 9

Inviscid CFD grid convergence test with number of boundary elements

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Figure 10

Model-scale wind tunnel test setup (dimensions in mm)

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Figure 11

Cpi distribution at the contraction inlet from viscous (RANS) CFD prediction, Re=7.2×106 (a) Floor and sides (b) Ceiling and sides

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Figure 12

Cpo Distribution at the contraction exit from viscous (RANS) CFD prediction, Re=7.2×106 (a) Floor and sides (b) Ceiling and sides

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Figure 13

Variation of minimum pressure coefficient, Cpo, near contraction outlet with the inlet second derivative and inflection point location from CFD prediction (a) Re=1.2×106 (minimum for existing tunnel) (b) Re=7.2×106 (maximum for existing tunnel)

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Figure 14

Variation of global minimum friction coefficient, Cf, near the contraction inlet with the inlet second derivative and inflection point location from CFD prediction (a) Re=1.2×106 (minimum for existing tunnel) (b) Re=7.2×106 (maximum for existing tunnel)

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Figure 15

Comparison of floor corner pressure distributions near the contraction inlet from viscous (RANS) and inviscid CFD predictions and experiment

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Figure 16

Comparison of floor corner pressure distributions near the contraction outlet from viscous (RANS) and inviscid CFD predictions and experiment

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Figure 17

Comparison of predicted minimum pressure near the contraction outlet from viscous (RANS) and inviscid CFD predictions and experiment

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Figure 18

Comparison of predicted contraction cavitation inception from viscous (RANS) and inviscid computations

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Figure 1

Floor profiles z(x), z′(x), and z″(x) from Eq. 1 with varying inflection location, x(z″=0), and entrance second derivative, z−1″=3

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Figure 2

Floor profiles z(x), z′(x), and z″(x) from Eq. 1 with varying inflection location, x(z″=0), and entrance second derivative, z−1″=0

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Figure 3

Variation of location and magnitude of maximum curvature near the contraction exit for practical values of inflection point location and inlet curvature

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Figure 4

Typical surface mesh for viscous CFD analysis for a maximum edge length (MEL) of 100mm and an inflated boundary thickness (IBT) of 50mm

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