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Research Papers: Multiphase Flows

Improvement of Hydrofoil Performance by Partial Ventilated Cavitation in Steady Flow and Periodic Gusts

[+] Author and Article Information
Jim Kopriva, Roger E. Arndt

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

Eduard L. Amromin

 Mechmath LLC, Prior Lake, MN 55372

J. Fluids Eng 130(3), 031301 (Mar 03, 2008) (7 pages) doi:10.1115/1.2842147 History: Received May 09, 2006; Revised December 31, 2007; Published March 03, 2008

This paper describes a study of the response of a recently developed low-drag partially cavitating hydrofoil (denoted as OK-2003) to periodical perturbations of incoming flow. A two-flap assembly specially designed to simulate sea wave impact on the cavitating hydrofoil generates the perturbations. The design range of cavitation number was maintained by ventilation. Unsteady flow can be simulated over a range of ratios of gust flow wavelength to cavity length. The measurement of time-average lift and drag coefficients and their fluctuating values over a range of inflow characteristics allows a determination of hydrofoil performance over a range of conditions that could be expected for a prototype hydrofoil. Both regular interaction with practically linear perturbations and resonancelike singular interaction with substantial nonlinear effects were noted. The observations are accompanied by a numerical analysis that identifies resonance phenomena as a function of excitation frequency.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 12

Measured drag coefficient of the hydrofoil OK-2003 at St=0.2. Squares relate to steady flow, triangles to 2deg of flap oscillation amplitude β, and rhombuses to β=4deg.

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Figure 15

Measured lift coefficient of the hydrofoil OK-2003 at St=0.4. Rhombuses relate to steady flow, squares relate to β=2deg, and triangles relate to β=4deg.

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Figure 16

Lift to drag ratio of the hydrofoil OK-2003 at St=0.4. Dotted line relates to steady flow, dashed line relates to β=2deg, and solid line relates to β=4deg.

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Figure 17

Frequency effect on normalized drag reduction of the ventilated hydrofoil OK-2003 at α=6deg and β=6deg. Drag is normalized to drag for noncavitating flow.

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Figure 13

Lift to drag ratio of the hydrofoil OK-2003 at St=0.2. Dashed line relates to steady flow, solid line relates to β=2deg, and dotted line relates to β=4deg.

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Figure 14

Measured drag coefficient of the hydrofoil OK-2003 at St=0.4. Rhombuses relate to steady flow, squares relate to β=2deg, and triangles relate to β=4deg.

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Figure 21

Coefficients describing thickness oscillation of the cavity tail versus St. Computation made for 4deg flap oscillations and σ=1.0.

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Figure 1

Hydrofoil contours of the OK-2003 and NACA-0015. The ideal cavity shape predicted by theory is also shown.

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Figure 2

Drag coefficient for natural and ventilated cavitations of the hydrofoil OK-2003 at α=6deg

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Figure 3

Lift to drag ratio for natural and ventilated cavitations of the hydrofoil OK-2003 at α=6deg

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Figure 4

Effect of airflow rate on the maximum values of average lift and fluctuating (rms) lift coefficients. U∞=8m∕s, while Pc and P∞ were tuned to maintain the maximum CL.

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Figure 5

Correlation between airflow rate Q and the total drag coefficient for cavitating hydrofoil OK-2003

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Figure 6

Schematic of two-flap gust generator (top) and view from the bottom of the apparatus in place. Note that the OK-2003 hydrofoil is cavitating in the absence of cavitation on the gust generator.

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Figure 7

Comparison of measured vertical velocity component (symbols) with its sinusoidal approximation (line)

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Figure 8

Dependencies of coefficients A0 and A1 on flap rpm for β=3deg flap oscillation amplitude shown on the top plot. Spanwise variation in oscillation amplitude A1 for β=4deg at 2400rpm shown on the bottom plot.

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Figure 9

Opposite phases (left and right) of a ventilated cavity on the hydrofoil OK-2003 at α=6deg and rpm=2400. The flow is from right to left.

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Figure 10

Opposite phases (left and right) of a ventilated cavity on the hydrofoil OK-2003 at α=7deg and rpm=1200. The flow is from right to left.

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Figure 11

Measured lift coefficient of the hydrofoil OK-2003 at St=0.2. Squares relate to steady flow, triangles to 2deg of flap oscillation amplitude β, and rhombuses to β=4deg.

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Figure 18

Measured rms pulsation of lift and drag for the ventilated hydrofoil OK-2003 at St=0.2. Lift pulsations are shown by triangles; drag pulsations are shown by squares. Data for β=4deg are shown by shaded symbols; data for β=2deg are shown by open symbols.

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Figure 19

Measured rms pulsation of lift and drag for the ventilated hydrofoil OK-2003 at St=0.4. Lift pulsations are shown by triangles; drag pulsations are shown by squares. Data for β=4deg are shown by shaded symbols; data for β=2deg are shown by open symbols.

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Figure 20

Cavity length L and cavity length pulsation amplitude dL on the ventilated OK-2003 hydrofoil for β=4deg. Squares show L values; triangles show dL. Shaded symbols relate to experimental data for St=0.4; open symbols relate to St=0.2. The dashed line for St=0.4 and the solid line for St=0.2 are computational results.

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