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Schedule for this lecture.
Goddard Space Flight Center Engineering Colloquium
Date: Monday, May 18, 1998
The very mechanism that traps a bubble in a standing acoustic wave causes it to execute an oscillatory translational motion in the direction of gravity. A bubble driven below resonance will move up during the collapse phase and down during the expansion phase. A bubble translating and collapsing develops a jet in the direction of motion. It is hypothesized that sonoluminescence is due to the collision of this jet with the other side of the bubble surface. The mechanism of light emission is a "fracture" process of the liquid that initially cannot respond by flowing due to the very short rise time of the applied pressure. The picosecond duration of the light flash is the time it takes for the microjet overpressure to be relieved by reflection from the microjet free surface. Several other observed features of sonoluminescence (such as noble gas and temperature sensitivity, anomalous mass loss process, effect of surfactants) can also be explained, at least qualitatively. A number of new and old experimental observations that support this picture will be discussed. (Work supported by the Office of Naval Research).
Andrea Prosperetti received his undergraduate degree in Physics (with an essay in elementary particle physics) summa cum laude from the University of Milano in 1968. With the help of a Fulbright Foundation grant, he went to Caltech for a Master's degree in 1971, and continued on for a doctorate that was awarded in 1974. Back in Milano, he was first Assistant and then Associate Professor of Physics jointly in the Physics Departments of the Engineering School and of the Faculty of Sciences. Since 1985 he has been Professor of Mechanical Engineering at the Johns Hopkins University. He was department chairman in the period 1988-1991 and was awarded the Charles A. Miller Distinguished Chair in Mechanical Engineering in 1994. He is a Fellow of the American Physical Society, the American Society of Mechanical Engineers, and the Acoustical Society of America. His expertise lies in the general area of multiphase flow, with concentration in bubble dynamics, disperse flows, and free-surface flows. He is also interested in underwater acoustics and thermoacoustic refrigeration. He is author or co-author of over 100 papers in refereed journals.
Colloquium Committee Sponsor: Jim Lobell
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