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ISBN 9783843913584

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978-3-8439-1358-4, Reihe Strömungsmechanik

Eric Lauer
Numerical simulation and investigation of high-speed bubble-dynamics in cavitating flow.

130 Seiten, Dissertation Technische Universität München (2013), Softcover, A4

Zusammenfassung / Abstract

The prevention or control of cavitation is of major interest in an increasing number of technical processes. These goals can only be achieved by a full understanding of the occurring mechanisms. For this purpose, we present a conservative sharp-interface method that includes a numerically efficient evaporation/condensation model. A level-set approach allows for an accurate tracking of the interface evolution throughout collapse and rebound of cavitation bubbles.

With a first set of simulations, we investigate the collapse of air-cavity arrays in water under shock wave loading with particular consideration of maximum pressures. As a general trend, we find a pressure amplification in consecutive cavity collapses. However, by increasing the number of cavities, we are able to demonstrate that the amplification is not monotonic. A parameter study of the cavity-separation distance in horizontal arrays shows that a smaller distance generally, but not necessarily, results in larger collapse pressures. Exceptions from the general trend are due to the very complex shock and

expansion-wave interactions and demonstrate the importance of using state-of-the-art numerical methods. By varying boundary conditions, we illustrate the significance of large test sections in experimental investigations.

Of high practical interest in cavitating flows is the collapse of vapor bubbles near walls since the large collapse pressures might lead to erosion. A non-equilibrium approach for phase-change in water enables the description of the differences in collapse evolution for detached and attached vapor bubbles. We show that the maximum wall pressure strongly depends on the symmetry of the collapse mechanisms, and regions with a high probability of bubble rebound are identified. Asymmetric attached bubbles lead to significantly different topology changes during collapse than symmetric bubbles but exhibit roughly the same range of maximum pressures.!