ZURUECK HOCH VOR INHALT SUCHEN

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Proposing Institution

Lehrstuhl für Aerodynamik, TU München
Project Manager

Dipl.-Ing. (Univ.) Bernd Budich
Boltzmannstr. 15
85748 Garching
Abstract
Phase transition from the liquid to a gaseous state within a fluid medium can happen either by heat addition, which is commonly known as boiling, or equally, by lowering the static pressure below the local vapor pressure, a phenomenon denoted as cavitation. Both processes result in the local evaporation of the liquid and the subsequent formation of vapor structures or cavities, which interact with the mean flow.When these vapor pockets, e.g. due to advection, reach flow regions of higher pressure, sudden implosion-like re-condensation of the vapor takes place. During these collapses, the surrounding fluid is accelerated towards the center of the vapor structure, or, under the presence of a material wall, will be focused on the structure. Due to the small compressibility of the fluid, pressure peaks with magnitudes of several GPa occur and strong shock waves are generated, which subsequently propagate through the liquid. The aggressiveness of these events can lead to material erosion of surfaces that are repeatedly exposed to cavitation and may eventually result in the failure of the affected mechanical systems.Many engineering applications are subjected to the phenomena of cavitation and cavitation erosion, including injector configurations of combustion engines or the propeller blades of naval propulsion systems. In the context of ship propellers, cavitation is highly undesirable. The erosive nature leads to increased cost for maintenance and overhaul. Additionally, performance of these devices is heavily impacted by the occurrence of cavitation. In order to better assess and control the influence on system performance, as well as to estimate erosion patterns and minimize failure probability, it is necessary to accurately predict the cavitation phenomenon.A key role for the detailed understanding of cavitation mechanisms and involved processes is the formation and propagation of complex shocks wave systems. These phenomena occur on length and time-scales which are several orders of magnitudes smaller than the characteristic scales of the convective mean flow. In order to accurately describe cavitating flows and their impact on the underlying structure by numerical simulations, it is a necessity to resolve these wave dynamics. However, the time- and length-scales between shock waves and the dimensions of the physical system under investigation typically span several orders of magnitudes, leading to substantial numerical effort. Furthermore, the mutual influences between boundary layers, fluid turbulence and the cavitation dynamics remain an open question, further adding to the complexity of the problem at hand. As a consequence, high fidelity numerical investigations requiring HPC resources are essential for addressing these issues.

Impressum, Conny Wendler