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Nuclei Population Dynamics and Cavitation

Liu, Zhenhuan (1995) Nuclei Population Dynamics and Cavitation. California Institute of Technology , Pasadena, CA. (Unpublished)

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The effect of the nuclei population in water on cavitation has not been investigated thoroughly due to the difficulties of measuring the microbubbles in water. In this thesis, a Phase Doppler Anemometer (PDA) was calibrated by a holographic method and used to measure the micro-bubble distribution in water. Agreement was achieved between the PDA and the holographic method. After the calibration, the PDA was used to study the nuclei population dynamics in two water tunnels. It was also employed in a study of cavitation on an axisymmetric Schiebe body in which the cavitation on the headform and the upstream nuclei population were simultaneously observed. Substantial changes in the nuclei number density distributions were found in these two water tunnels. The nuclei population in each water tunnel can also vary significantly, sometimes by as much as an order of magnitude. The nuclei population dynamics are complicated and are affected by the tunnel design, the tunnel operating condition and the air content. The cavitation event rate on the Schiebe headform is mainly determined by the cavitation number. It increases dramatically as the cavitation number is decreased. It also varies with the magnitude and the shape of the nuclei number distribution. As the upstream nuclei population increases, the cavitation event rate increases. During the experiments, cavitation acoustic emissions were also measured and analyzed. An analytical model based on the spherical bubble assumption and the Rayleigh-Plesset theory is developed to relate the free stream nuclei population to the cavitation event rate and the acoustic noise on an axisymmetric body. Complications, such as the effect of the boundary layer flow rate, of the bubble screening, of the bubble/bubble interactions and of the observable bubble size are examined and included in the model. The predicted cavitation event rate and acoustic impulse are compared with the experimental observations. It is shown that the predicted event rates agree with the observations when the population is small, but that increasing discrepancies occur at lower cavitation numbers when the bubble density becomes larger. The predicted noise qualitatively agrees with the observations, but is generally larger than the observations, mainly due to the fact that the spherical bubble assumption usually departs from the observed bubble shape.

Item Type:Report or Paper (Technical Report)
Additional Information:©1994 Zhenhuan Liu. Report No. ENG 200.31 on contracts N00014-85-K-0397 N00014-91-K-1295. There are many people who have played a role during the course of this work. I would like to thank my advisors, Dr. Christopher Brennen and Dr. Allan Acosta, whose professional guidance, encouragement and patience made this work possible. My thanks also go to my colleagues, especially to Dr. Kotara Sato, Dr. Yan Kuhn de Chizelle, Dr. Douglas Hart, Garrett Reisman, Yi-Chun Wang, Elizabeth McKenney and Fabrizio D'Auria. I gratefully acknowledge the assistance of the professional staff of Caltech, especially Pavel Svitek, Marty Gould, Joseph Fontana and Richard Eastvedt. Funding for this work was provided by the Office of Naval Research under contract number N-00014-85-K-0397 and N-0014-91-k-1295. This support is gratefully acknowledged. Finally, I dedicate this thesis to my wife, Hongyu Piao.
Funding AgencyGrant Number
Office of Naval Research (ONR)N-00014-85-K-0397
Office of Naval Research (ONR)N-00014-91-K-1295
Subject Keywords:cavitation, bubble dynamics, bubble acoustics, cavitation nuclei, Phase Doppler Anemometer
Record Number:CaltechAUTHORS:20140429-144019490
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45322
Deposited On:30 Apr 2014 21:47
Last Modified:03 Oct 2019 06:29

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