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TECHNICAL PAPERS

Dynamics and Intensity of Erosive Partial Cavitation

[+] Author and Article Information
Xavier Escaler

Center for Industrial Diagnostics (CDIF), Universitat Politècnica de Catalunya (UPC), Avinguda Diagonal 647, 08028 Barcelona, Spainescaler@mf.upc.edu

Mohamed Farhat

Laboratory for Hydraulic Machines (LMH-IMHEF), École Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerlandmohamed.farhat@epfl.ch

Eduard Egusquiza

Center for Industrial Diagnostics (CDIF), Universitat Politècnica de Catalunya (UPC), Avinguda Diagonal 647, 08028 Barcelona, Spainegusquiza@mf.upc.edu

François Avellan

Laboratory for Hydraulic Machines (LMH-IMHEF), École Polytechnique Fédérale de Lausanne (EPFL), Avenue de Cour 33bis, CH-1007 Lausanne, Switzerlandfrancois.avellan@epfl.ch

J. Fluids Eng 129(7), 886-893 (Jan 15, 2007) (8 pages) doi:10.1115/1.2742748 History: Received October 13, 2006; Revised January 15, 2007

An experimental work has been carried out to investigate the dynamic behavior and the intensity of erosive partial cavitation on a 2-D hydrofoil. Both sheet (stable) and cloud (unstable) cavitation have been tested in a cavitation tunnel for various free stream velocities. Special attention has been given to validate the use of acceleration transducers for studying the physical process. In particular, the modulation in amplitude of the cavitation induced vibrations in a high frequency band has allowed us to determine the shedding frequency and the relative intensity of the collapse process for each testing condition. Regarding the cavity dynamics, a typical Strouhal value based on its length of about 0.28 has been found for cloud cavitation; meanwhile, for sheet cavitation, it presents a value of about 0.16. Furthermore, the level of the vibration modulation in the band from 45kHz to 50kHz for cloud cavitation shows a power law dependency on the free stream velocity as well as a good correlation with the pitting rate measured on stainless steel samples mounted on the hydrofoil.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cross sections of the plane-convex (top) and of the NACA 65012 (bottom) hydrofoils

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Figure 2

Partial cavitation on a 2-D hydrofoil. Top: Sheet cavitation at Uinf=30m∕s, σ=0.7, and i=2deg. Bottom: Cloud cavitation at Uinf=30m∕s, σ=1.2, and i=5deg. Flow from left to right.

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Figure 3

Section of the hydrofoil, the revolving bedplate, and the support for the accelerometers. Schematic of the transducer locations and orientations.

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Figure 4

Filtered time signal and corresponding envelope of cavitation induced vibrations in the band from 45kHz to 50kHz (i=6deg, Uinf=30m∕s, l∕c=0.4, and σ=1.6)

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Figure 5

PSD (top) and modulation in the band from 45kHz to 50kHz (bottom) of cloud cavitation vibrations measured on the plane-convex hydrofoil with BKV, KV, and KH (i=0.8deg, Uinf=35m∕s, l∕c=0.5, and σ=0.6)

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Figure 6

PSD (top) and modulation in the band from 45kHz to 50kHz (bottom) of cloud cavitation vibrations measured on the plane-convex hydrofoil with two KH at different distances (i=5deg, Uinf=35m∕s, l∕c=0.3, and σ=1.1)

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Figure 7

Modulation results (top) and comparison of their amplitudes relative to the baselines (bottom) for different frequency bands (in kHz) of cloud cavitation vibrations measured on the NACA hydrofoil with BKV (i=6deg, Uinf=30m∕s, l∕c=0.4, and σ=1.6)

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Figure 8

PSD of the cavitation induced vibrations on the NACA hydrofoil

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Figure 9

Comparison of PSD at two incidence angles for the same l∕c=0.4 (top) and at two cavity lengths for the same i=6deg (bottom) for Uinf=30m∕s on the NACA hydrofoil

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Figure 10

Overall mean square value of accelerations as a function of Uinf in the band from 45kHz to 50kHz on the NACA hydrofoil

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Figure 11

PSD of vibration modulation spectra in the band from 45kHz to 50kHz on the NACA hydrofoil

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Figure 12

Mean square level of the vibration modulation as a function of Uinf in the band from 45kHz to 50kHz on the NACA hydrofoil

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Figure 13

Average pitting rate on stainless steel as a function of mean square level of the vibration modulation in the band from 45kHz to 50kHz at i=6deg and linear fit for the NACA hydrofoil

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