Cavity Collapse at Spherical Free Surfaces in Microgravity
- Paper number
IAC-05-A2.1.04
- Author
Mr. Danail Obreschkow, European Space Agency/Student Participation Programme, United Kingdom
- Year
2005
- Abstract
it REMARK: Our project contains an experimental proposal that was designed for ESA’s student parabolic flight campaign 2005. Yet, the underlying theory and our ground-based experiments reveal new physical insight, independently from the admission to the parabolic flight campaign.
Turbulent liquid flows are subject to the formation of small vapor cavities, which implode rapidly. Because of its high complexity this "cavitation" phenomenon is only partially understood. Yet, cavitation is a major concern in the design of turbo-machines and cryogenic pumps for rocket propulsion. It causes strong vibrations, serious efficiency loss and erosion damage. Those phenomena are associated with shock waves and microjets formed during the cavity implosion. Both features have been investigated for many years at the Laboratory of Hydraulic Machines (LMH) at the Swiss Federal Institute of Technology (EPFL).
In collaboration with LMH, we have recently studied vapor cavities next to planar free surfaces of water. These cavities were created using electrical discharges, which generate a small plasma inside the water. The plasma suddenly expands and gives rise to a vapor cavity of 8mm in diameter. During the subsequent cavity implosion we could observe the formation of a microjet and for the first time measure its volume and velocity (see illustration at it www.quantumholism.com/cavitation). These results give insight in the physics of the last stage of cavity implosion, which is hardly understood nowadays. Further, our experiments and theoretical investigations have revealed the importance of studding cavities next to SPHERICAL surfaces of water. However, nobody has ever produced cavities next to spherical surfaces due to the difficulty of creating such surfaces in the presence of gravity.
Our next goal is to study the cavity implosion and microjet formation next to a spherical free surface of water, realized in microgravity. During the cavity implosion we expect to observe the formation of a microjet, which is probably highly different from the one next to a planar surface. In particular, a second microjet in the opposite direction is predicted theoretically.
Based on our ground-based experiment, we have developed a microgravity experiment, which is currently proposed for ESA’s "8th student parabolic flight campaign". Let us give a short description of the experiment: A micro-pump allows us to generate a spherical bubble of water in microgravity. Precisely, a volume of 1ml to 5ml of water is expelled over 10s to 15s. Thereby we generate a stable spherical bubble of 1cm to 2cm in diameter, held together by surface tension. Once the bubble is formed, an electrical charge is released between two electrodes that penetrate the bubble. This creates a small plasma inside the water sphere that blows up to a cavity in some microseconds. Its diameter can be varied from 2mm to 8mm, as observed in our ground-based experiments (see above). Some microseconds after its formation, the cavity will implode and create one or eventually several microjets. The cavity generation, the implosion and the microjet formation will be filmed with a "Photron" high-speed camera.
- Abstract document
- Manuscript document
IAC-05-A2.1.04.pdf (🔒 authorized access only).
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