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Research Papers: Multiphase Flows

# An Assessment of the Influence of Environmental Factors on Cavitation Instabilities

[+] Author and Article Information
Damien T. Kawakami, A. Fuji, Y. Tsujimoto

University of Minnesota, Mississippi River at 3rd Ave. S.E., Minneapolis, MN 55414

R. E. Arndt1

University of Minnesota, Mississippi River at 3rd Ave. S.E., Minneapolis, MN 55414arndt001@umn.edu

They were manufactured in the same shop by the same machinist.

1

Corresponding author.

J. Fluids Eng 130(3), 031303 (Mar 10, 2008) (8 pages) doi:10.1115/1.2842146 History: Received July 03, 2005; Revised December 28, 2007; Published March 10, 2008

## Abstract

Cavitation induced flow instabilities are of interest in numerous applications. Experimental and numerical investigations of this phenomenon are taking place at several institutions around the world. Although there is qualitative agreement among the numerous recent papers on the subject, there is a lack of agreement with regard to important details, such as the spectral content of unsteady lift oscillations. This paper summarizes observations of a cavitating NACA0015 foil in three different tunnels that revealed remarkably different cavity shedding appearances and behaviors. Some of the differences were attributed to system instabilities. However, in addition to a different cavitation behavior attributed to system instabilities, it was found that differences in gas content could significantly alter the lift spectrum of a cavitating foil. For a certain range of the composite parameter $σ∕2α$ near 4, the dominant frequency appears to double when the gas content is reduced by a half. It is also argued that surface effects can have a significant influence on fully wetted time during cavity shedding. Normally, surface effects are assumed to play an important role in the initial inception of a fully wetted hydrofoil with gas content being the primary factor governing developed cavitation behavior. However, the repetitive nature of the process implies that each shedding cycle is an individual inception process. Hence, the unexpected role of surface effects in partially cavitating hydrofoils. The conclusions reached have important ramifications concerning numerical code verification that is a topic of major concern.

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## Figures

Figure 1

Types of cavitation found on the NACA 0015 hydrofoil

Figure 2

Spectra of measured lift oscillations (3)

Figure 3

Comparison between Sato (12) and Arndt (3) data for a cavitating hydrofoil. l∕c is the ratio of upstream duct length to chord length.

Figure 4

Sketch of the Obernach cavitation tunnel and its essential components

Figure 5

Sketch of the SAFL water tunnel

Figure 6

Osaka water tunnel

Figure 7

Cavitation cycle for anodized foil σ=1.0, α=8deg(σ∕2α=3.58), and gas content ∼13ppm in the SAFL tunnel (plan and profile view)

Figure 8

Cavitation cycle for σ=1.0 and α=8deg(σ∕2α=3.58) in the Osaka tunnel (plan and profile view)

Figure 9

Cavitation cycle for σ=1.0 and α=8deg(σ∕2α=3.58) in the Obernach tunnel (plan view). Note the leading edge is visible on the right edge of each image.

Figure 10

NACA0015 fully wetted time normalized by period for three tunnels (Note: SAFL results show no fully wetted leading edge)

Figure 11

Observed shedding frequency for three tunnels

Figure 12

Comparison of pressure and lift spectra for the NACA0015 foil observed in three tunnels: (a) unsteady lift—Obernach tunnels; (b) Unsteady lift—SAFL tunnel (anodized, ∼13ppm); (c) upstream strain gage—Osaka tunnel

Figure 13

Comparison of SAFL anodized foil unsteady lift spectra for high and low gas content. The intensity of shading corresponds to amplitude: (a) high gas content (b) low gas content

Figure 14

Comparison between lift spectrum and suction side surface pressure fluctuations for high and low gas contents: (a) high gas content—SAFL lift balance; (b) High gas content—SAFL instrumented foil; (c) low gas content—SAFL lift balance; (d) low gas content—SAFL instrumented foil.

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