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Multiphase Flows

Numerical and Experimental Study of the Interaction of a Spark-Generated Bubble and a Vertical Wall

[+] Author and Article Information
Arvind Jayaprakash1

 DYNAFLOW , INC ., 10621-J Iron Bridge Road, Jessup, MD 20794arvind@dynaflow-inc.com

Chao-Tsung Hsiao

 DYNAFLOW , INC ., 10621-J Iron Bridge Road, Jessup, MD 20794ctsung@dynaflow-inc.com

Georges Chahine

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

1

Corresponding author.

J. Fluids Eng 134(3), 031301 (Mar 19, 2012) (12 pages) doi:10.1115/1.4005688 History: Received February 11, 2011; Revised November 30, 2011; Published March 16, 2012; Online March 19, 2012

An understanding of the fundamental mechanisms involved in the interaction between bubbles and structures is of importance for many applications involving cavitation erosion. Generally, the final stage of bubble collapse is associated with the formation of a high-speed reentrant liquid jet directed toward the solid surface. Local forces associated with the collapse of such bubbles can be very high and can exert significant loads on the materials. This formation and impact of liquid jet is an area of intense research. Under some conditions, the presence of gravity and other nearby boundaries and free surfaces alters the jet direction and need to be understood, especially that in the laboratory, small scale tests in finite containers have these effects inherently present. In this work, experiments and numerical simulations of the interaction between a vertical wall and a bubble are carried out using Dynaflow’s three-dimensional code, 3DYNA FS-BEM , which models the unsteady dynamics of a liquid flow including the presence of highly nonlinear time evolving gas-liquid interfaces. The numerical predictions were validated using scaled experiments carried out using spark generated bubbles. These spark bubble tests produced high fidelity test data that properly scale the fluid dynamics as long as the geometric nondimensional parameters, gravity and time are properly scaled. The use of a high speed camera allowing framing rates as high as 50,000 frames per second to photograph the bubbles produced high quality observations of bubble dynamics including clear visualizations of the reentrant jet formation inside the bubble. Such observations were very useful in developing and validating the numerical models. The cases studied showed very good correlation between the numerical simulations and the experimental observations and allowed development of predictive rules for the re-entrant jet characteristics, including jet angle, jet speed, and various geometric characteristics of the jet.

Copyright © 2012 by American Society of Mechanical Engineers
Topics: Bubbles
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Figures

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Figure 1

Definition sketch of the parameters of the problem of a bubble dynamics near a vertical wall, a free surface, and a rigid bottom

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Figure 2

Quantities used to characterize a collapsing bubble reentrant jet

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Figure 3

Evolution of the bubble diametrical contours. The left panel shows a bubble growth sequence, while the right panel shows bubble collapse and reentrant jet formation. Contours are shown a regular time step intervals not equal times (time steps are very much reduced during the bubble collapse period). The bubble initial center is at a depth of 12 cm, the tank pressure over the free surface is 12,200 Pa, the initial gas pressure is 6.6 × 109 Pa, and the initial bubble radius is 0.1 mm.

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Figure 4

Normalized reentrant jet dimensions as a function of time for the bubble of Fig. 3

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Figure 5

Normalized reentrant jet shape factor for the bubble of Fig. 3

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Figure 6

Normalized jet speed as a function of time. Various definitions of the jet as described in the text, Eqs. 20 to 22. Same conditions as bubble in Fig. 3.

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Figure 7

Schematic of a Dynaflow’s spark cell setup for single and multiple bubble dynamics study

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Figure 8

A picture of the large Dynaflow’s spark-generated bubbles test facility. The Plexiglas tank dimensions are 1 m × 1 m × 1 m and the wall thickness is 2.5 cm. The tank can support internal pressure as low as 3500 Pa.

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Figure 9

Pressures recorded on the rigid wall at the end of the bubble collapse for two repeated runs. The experimental conditions are: Electrode depth of 15 cm from free surface; 1.7 cm from the vertical wall, bottom depth of 24 cm, and cell pressure of 7270 Pa.

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Figure 10

Snapshots of spark bubble and corresponding 3DYNA FS-BEM bubble for the electrode depth of 6 cm from free surface; 0.85 cm from simulated wall, depth of 12 cm, and cell pressure of 12,200 Pa. The nondimensional stand-off = 0.65 Rmax .

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Figure 11

Comparison of the evolution of the bubble equivalent radii between scaled spark tests and corresponding 3DYNA FS-PHANTOMCLOUD and 3DYNA FS-BEM simulations using R0  = 0.04 cm, Rmax  = 1.38 cm, and Patm  = 12,200 Pa. This corresponds to the conditions of Fig. 1.

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Figure 12

Snapshots of spark bubble and corresponding 3DYNA FS-BEM bubble for the electrode depth of 6 cm from free surface; 2 cm from simulated wall, depth of 12 cm, and cell pressure of 12,200 Pa. The nondimensional stand-off = 1.5 Rmax .

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Figure 13

Comparison of the evolution of the bubble equivalent radii between scaled spark tests and corresponding 3DYNA FS-PHANTOMCLOUD and 3DYNA FS-BEM simulations using R0  = 0.04 cm, Rmax  = 1.35 cm, and Patm  = 12,500 Pa. This corresponds to the conditions of Fig. 1.

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Figure 14

Cross-cut of bubble shape at touchdown for various stand-off distances from the wall. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa. Also shown are the bubble initial locations.

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Figure 15

Variation of jet angle for various standoff distances. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa.

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Figure 16

Normalized curves of variation of jet radii and jet height for various standoff distances. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa.

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Figure 17

Normalized curves of variation of jet volume for various standoff distances. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa.

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Figure 18

Normalized curves of variation of jet averaged velocities for various stand-off distances. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa.

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Figure 19

Normalized curves of variation of jet momentum for various stand-off distances. The simulation conditions are: R0  = 1.17 cm, Rmax  = 16.48 cm, D = 121.92 cm, and Patm  = 101,230 Pa.

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