August 11th, 10:00 AM EDT - 10:45 AM EDT
Technical
Dr. Steven Ceccio
Lecture Title: The Role of Compressibility on the Dynamics of Developed Cavitation
Abstract: Developed cavitation can occur on liquid flows over lifting surfaces, in the passages of turbomachinery, and in the wakes of bluff bodies. Such cavitation can be very deleterious to system performance, leading to thrust breakdown, vibration, and erosion. Alternatively, pockets of developed cavitation can be actively employed to reduce hydrodynamic resistance. The cyclical shedding of large-scale vapor and gas clouds (cloud cavitation) is an important feature of these flows, and the mechanisms responsible for sheet-to-cloud transition has received considerable study. Re-entrant liquid flow has traditionally been identified and the dominant mechanism for the creation of unstable sheet cavitation, but recent studies have revealed that a second important process is responsible for flow instability. High volume-fraction bubbly mixtures exhibit compressibility and can manifest sound speeds that are very low compared to the freestream speed of the flow. When this occurs, the local Mach number (based on local speed of sound) within the region of bubbly flow can exceed unity, leading to the formation of dynamic condensation waves. We have shown how this process leads to sheet to cloud transition, and how consideration of the local Mach number can explain a variety of previously observed flow cavity flow phenomena that cannot be explained simply with re-entrant flow dynamics. We have visualized these cavitating flows using traditional optical and cinematographic X-ray imaging. In the present talk we will explore the importance of compressibility on cavity dynamics for flows over a variety of canonical bodies and discuss the relationship between the cavitating mixture properties, the resulting sound speed (Mach number), and the formation of bubbly shock waves. We will also show how the injection of non-condensable gas can be used to suppress these flow dynamics by lowering the local mixture Mach number.
Presentations
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