Hydrodynamics, Acoustics and Scaling of Traveling Bubble Cavitation
Recent observations of the geometries of growing and collapsing bubbles over axisymmetric headforms have revealed the complexity of the "microfluidmechanics" associated with these flows (Hamilton et al., 1982, Briançon Marjollet and Franc, 1990, Ceccio and Brennen, 1991). Among the complex features observed were bubble to bubble interaction, cavitation noise generation and bubble interaction with the boundary layer which leads to the shearing of the underside of the bubble and alters the collapsing process. All of these previous tests were performed on small headform sizes. The focus of this research is to determine the dynamics governing the growth and collapse of traveling bubbles and to analyze the scaling effects due to variations in geometry size, Reynolds number and cavitation number. For this effect, cavitating flows over Schiebe headforms of different sizes (5.08cm, 25.4cm and 50.8cm in diameter) were studied in the David Taylor Large Cavitation Channel (LCC). This thesis presents the scaling effects captured on high-speed film and electrode sensors as well as the noise signals generated during the collapse of the cavities. The influence of each of these parameters on the dynamics involved in the growth and collapse phases of the traveling bubble are presented, along with the acoustical impulse produced during the collapse of the bubble. In order to model and analyze the dynamics of the three-dimensional bubble deformation in the presence of the pressure field around the Schiebe headform, an unsteady numerical code using traveling sources has been developed. This thesis presents calculations of the interaction between the irrotational flow outside the boundary layer of the headform and individual traveling bubbles. An error estimation of the method and comparisons with the LCC experiments are presented. This method is shown to predict some of the features of three-dimensional bubble growth and collapse dynamics remarkably well. Furthermore, analysis of these computations allow a better understanding of bubble interaction and event rate prediction.
Report No. ENG 200.30 on contracts N00014-91-J-1295, N00014-91-J-1426. First I would like to thank all of those who encouraged me to pursue my research work at Caltech. In chronological order these are my girlfriend (and now wife) Anh-Ngoc, my parents, Dr. François Avellan at EPFL who initiated me to the excitement of research and Dr. Allan Acosta who made my coming here possible. I cannot enumerate here the long list of fantastic friends and coworkers who made my stay in sunny California so pleasant and unforgettable along with those who helped me throughout my thesis work and I thank them from the bottom of my heart. Among them I would especially like to mention Petr Pich, Garrett Reisman, Carl Wassgren, Douglas Hart, Elizabeth McKenney and Zhenhuan Liu. I wish to express my deepest gratitude to my advisors Dr. Christopher Brennen and Dr. Allan Acosta for their continuing help and professional guidance. The experiments performed in the LCC required help of many people and I am very grateful to all those who were involved in this enterprise, particularly to Dr. Steve Ceccio and Po-Wen Yu from the University of Michigan and to Dr. Young Shen, Scott Gowing, Jim Blanton and Bob Etter from the David Taylor Research Center. I also thank the Office of Naval Research for funding this work under contract N00014-91-J-1295. Finally I dedicate this thesis to my loving wife, Anh-Ngoc and to the small island, Ile d'Arz, off the coast of Brittany (France) where we got married.
Published - Report_No._ENG_200.30.pdf