Abstract
A liquid jet is of fundamental interest as a canonical multiphase-flow phenomenon to study free-surface motion as well as of great importance in industrial/medical processes. This seminar introduces a liquid jet and cavitation induced by a large acceleration via impulsive force. Remarkably, a simple device employing such an impulsive force is able to generate a highly-viscous jet of 10,000 mm^2/s, which is as viscous as honey. The onset of cavitation in the accelerated liquid is found to enhance the jet velocity significantly. The fluid dynamics behind is elucidated by dividing the jet generation process into two parts that occur in different time scales; the impact interval, in which the liquid accelerates due to the impact, and the focusing interval, in which the liquid jet emerges via flow focusing. The threshold of acceleration-induced cavitation (renewed Cavitation number) is derived from the equation of motion. For practical application of the jets, an effective way to control the cavitation effect on the jet velocity is suggested using preformed bubbles in soft materials.

About the Presenter
Yoshiyuki Tagawa did his undergraduate and graduate studies at The University of Tokyo in Japan. He was a Japan Society for the Promotion of Science Research Fellow at The University of Tokyo, a postdoctoral fellow at the University of Twente in the Netherlands for 2010-2012. Since 2013, Dr. Tagawa has been a principal investigator in the Department of Mechanical Systems Engineering at the Tokyo University of Agriculture and Technology and served as a Professor from 2020. Dr. Tagawa's original contribution is his work in proposing a method for creating a focused liquid jet, which is a complex phenomena on the basis of free surface flow dynamics, bubble dynamics and microfluidics. As a result of his accomplishments, he received the Andrea Prosperetti Award 2019, and was Distinguished Young Researcher 2016 of the Japanese Society of Multiphase Flow, among others awards. He has served on Editorial Advisory Board of the International Journal of Multiphase Flow and the national (Japan) board of The Japan Society of Multiphase Flow.

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