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Research Papers: Multiphase Flows

Cavitation Inception in the Wake of a Jet-Driven Body

[+] Author and Article Information
Roger E. A. Arndt, William Hambleton

University of Minnesota, 2 Third Avenue SE, Minneapolis, MN 55414

Eduard L. Amromin

Mechmath LLC, 14530 Bluebird Trail, Prior Lake, MN 55372-1283

J. Fluids Eng 131(11), 111302 (Oct 27, 2009) (8 pages) doi:10.1115/1.4000388 History: Received August 19, 2008; Revised September 28, 2009; Published October 27, 2009

Abstract

Although cavitation inception in jets has been studied extensively, little is known about the more complex problem of a jet flow interacting with an outer flow behind a moving body. This problem is studied experimentally by considering inception behind an axisymmetric body driven by a waterjet. Tests were carried out for various water tunnel velocities and jet speeds such that jet velocity ratio $UJ/U$ could be varied in the range of 0–2. Distinctly different cavitation patterns were observed at zero jet velocity (when cavitation appeared in spiral vortices in such flows) and at various jet velocity ratios (when cavitation appeared around the jet in such flows). A simple superposition analysis, utilizing particle imaging velocimetry (PIV) measurements, is able to qualitatively predict the experimental result. On the basis of these observations, a numerical prediction of cavitation inception number based on viscous-inviscid interaction concept is suggested.

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Figures

Figure 1

Cavitation inception index for coflowing jets (1) at two ratios of coflow speed to the jet initial velocity

Figure 2

Experimental setup including the test body, mounting strut, and force balance

Figure 3

Side view of test body

Figure 4

Pressure distribution around the nose of the Schiebe body

Figure 5

Schematic of flow pattern. The boundary between jet and wake behind the transom is shown by a dashed line.

Figure 6

Mean velocity measurements illustrating wake development at Uj/U=0 (left) and Uj/U=1.5 (right). The distances shown are in mm.

Figure 7

Mean streamlines and photos of cavitation for velocity ratios of 0 (left) and 1.5 (right). The distances shown are in mm.

Figure 8

PIV data. Mean velocity is shown on the left and turbulent stress ⟨u′v′⟩(m2/s2) is shown on the right. The distances shown are in mm.

Figure 9

Cavitation patterns for different Uj at the same U and water tunnel pressure. Top photo corresponds to Uj/U=0, center photo corresponds to Uj/U=1, and bottom photo corresponds to Uj/U=2.

Figure 10

Cavitation inception data

Figure 11

Schematic of cavitation inception as influenced by the interaction of the jet and the surrounding wake

Figure 12

Comparison of theoretical and measured dimensionless circumferential velocity 2πwRC/Γ in the vortex core. The solid line corresponds to Eq. 7, and the dashed line corresponds to a laminar viscous core with linear dependency of the velocity w on the dimensionless radius ς. Experimental data are shown by symbols.

Figure 13

Computed dependency of cavitation number on bubble radius

Figure 14

Computed velocity profiles in the wake at U=5 m/s. The velocity profiles u(r/δ) have minima at x=1.05L and x=2.2L. Such minima are inherent neither to jets discharged in immobile water nor to wakes behind towed bodies.

Figure 15

Measured dependency ⟨u′v′⟩ on Re for a wake

Figure 16

Comparison of computed (lines) and measured (symbols) (1) cavitation inception indexes versus Reynolds number (calculated using the average of the jet and coflow speeds as a characteristic velocity). The comparison is made for Uj/U=4/3 and 1.

Figure 17

Comparison of computed (lines) and measured (symbols) values of cavitation inception index versus jet speed for Schiebe body at two freestream speeds

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