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TECHNICAL PAPERS

Characterization of the Content of the Cavity Behind a High-Speed Supercavitating Body

[+] Author and Article Information
Xiongjun Wu1

 Dynaflow Inc., 10621-J Iron Bridge Road, Jessup, MD 20794wxj@dynaflow-inc.com

Georges L. Chahine

 Dynaflow Inc., 10621-J Iron Bridge Road, Jessup, MD 20794glchahine@dynaflow-inc.com

1

Corresponding author.

J. Fluids Eng 129(2), 136-145 (Jul 14, 2006) (10 pages) doi:10.1115/1.2409356 History: Received January 04, 2006; Revised July 14, 2006

A high speed/high flow test facility was designed and implemented to study experimentally the supercavitating flow behind a projectile nose in a controlled laboratory setting. The simulated projectile nose was held in position in the flow and the cavity interior was made visible by having the walls of the visualization facility “cut through” the supercavity. Direct visualization of the cavity interior and measurements of the properties of the cavity contents were made. Transducers were positioned in the test section within the supercavitation volume to enable measurement of the sound speed and attenuation as a function of the flow and geometry parameters. These characterized indirectly the content of the cavity. Photography, high speed videos, and acoustic measurements were used to investigate the contents of the cavity. A side sampling cell was also used to sample in real time the contents of the cavity and measure the properties. Calibration tests conducted in parallel in a vapor cell enabled confirmation that, in absence of air injection, the properties of the supercavity medium match those of a mixture of water vapor and water droplets. Such a mixture has a very high sound speed with strong sound attenuation. Injection of air was also found to significantly decrease sound speed and to increase transmission.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the experimental simulation of the supercavitation behind a projectile. On the left (a) two configurations for the simulated projectile head placement in the visualization facility are shown with the arrows indicating the viewing angle. On the right (b) a sketch of the developed cavity and the viewing angle and placement of measurement transducers are shown.

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Figure 2

Sketch of the experimental facility setup

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Figure 3

Side view of the test section with dimensions in cm, A1 and A2 are air supply ports, S1–S4 are sensor mounting ports, and M is the projectile mounting port

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Figure 4

Evolution of the cavitating flow with decreasing cavitation numbers (here increasing flow rates). (a)Q=15.8L∕s (250 gpm), V≃8m∕s, σ∼0.13; (b)Q=22.1L∕s (350 gpm), V≃11m∕s, σ∼0.07; (c)Q∼34.7L∕s (550 gpm), V≃18m∕s, σ∼0.02.

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Figure 5

Effects of the projectile shape on the cavity formation. Q∼31.6L∕s (500 gpm), V≃16m∕s, σ∼0.03. The vortices above the supercavity are the horseshoe vortices formed near the projectile.

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Figure 6

Top view of different types of projectile shaped leading edge that were tested to minimize the secondary horseshoe vortex

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Figure 7

Cavities with air ventilation. (a) Air injection towards upstream. (b) Air injection towards downstream. Q∼31.6L∕s (500 gpm), V≃16m∕s. The vertical line and horizontal arrow indicates the approximate position of the injector and the direction of the injection, respectively.

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Figure 8

Supercavity formed from a 1∕2 projectile mounted on the top of the test section. (a) Formation of a reentrant jet, Q∼31.6L∕s (500 gpm), V≃16m∕s, σ∼0.03. (b) Cavity vented to the atmosphere, Q∼31.6L∕s (500 gpm), V≃16m∕s.

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Figure 9

Supercavity with reentrant jet formed from a full projectile mounted in the middle of the test section. Q∼34.7L∕s (550 gpm), V≃15m∕s, σ∼0.03.

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Figure 10

Setup for direct sound speed measurement in the test section

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Figure 11

Typical signals from optical sensor and hydrophone

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Figure 12

Sound speed in the test section under various conditions as indicated on labels

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Figure 13

Peak amplitude of signal in test section under various conditions as indicated on labels

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Figure 14

Sketch of the setup for measurements in the side sampling cell

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Figure 15

Sound speed as measured in the side sampling cell for increasing amounts of ventilation or supercavity pressures, Dataset 1 and Dataset 2 were conducted at two different dates

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Figure 16

Peak amplitude of signal measured in the side sampling cell for increasing amounts of ventilation or supercavity pressures, Dataset 1 and Dataset 2 were conducted at two different dates

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Figure 17

A sketch of the setup for measurement in the vapor cell. Both contents of the cell (vapor and air) and pressure were controlled.

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Figure 18

Sound speed in the vapor cell for various cell pressures or amounts of air/vapor mixtures, Dataset 1 and Dataset 2 were conducted at two different dates

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Figure 19

Peak amplitude of signal in the vapor cell for various cell pressures or amounts of air/vapor mixtures, Dataset 1 and Dataset 2 were conducted at two different dates

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Figure 20

Variation of sound speed with the pressure in the test cell or the cavity. Cavity and cell pressures increase are achieved by increasing air injection.

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