We are comparing results of numerical simulations against high speed simultaneous observations of cavitation and cavitation erosion. We performed fully compressible, cavitating flow simulations to resolve the formation of the shock waves at cloud collapse % these are believed to be directly related to the formation of the damage. Good agreements were noticed between calculations and tests. Two high pressure peaks were found during one cavitation cycle. One relates to the cavitation collapse and the other one corresponds to the cavitation shed off, both contributing to a distinctive stepwise erosion damage growth pattern. Additional, more precise, simulations with much shorter time step were performed to investigate the processes of cavitation collapse and shedding off in more detail. There the importance of small cavitation structures which collapse independently of the main cloud was found. The present work shows a great potential for future development of techniques for accurate predictions of cavitation erosion by numerical means only.
COBISS.SI-ID: 13879067
Recently van Rijsbergen et al. (2012), by simultaneous observation of cavitation and acoustic emission measurements, and Petkovsek and Dular (2013), by simultaneous observation of both cavitation structures and cavitation damage, have pointed to the fact that the small scale structures and the topology of the cavitation clouds play a significant role in cavitation erosive potential. Despite the two, before mentioned, studies opened some new insights to the physics of cavitation damage, many new questions appeared. In the present study we attached a thin aluminum foil to the surface of a transparent Venturi section using two sided transparent adhesive tape. The surface was very soft - prone to be severely damaged by cavitation in a very short period of time. Using high speed cameras, which captured the images at 30,000 frames per second, we simultaneously recorded cavitation structures (from several perspectives) and the surface of the foil. Analysis of the images revealed that five distinctive damage mechanisms exist - spherical cavitation cloud collapse, horseshoe cavitation cloud collapse, the twister cavitation cloud collapse and in addition it was found that pits also appear at the moment of cavitation cloud separation and near the stagnation point at the closure of the attached cavity.
COBISS.SI-ID: 14036763
A new algorithm for fast DNS cavitating flows simulations is developed. The algorithm is based on Kim and Moin projection method form. Homogeneous mixture approach with transport equation for vapour volume fraction is used to model cavitation and various cavitation models can be used. Infuence matrix and matrix diagonalisation technique enable fast parallel computations.
COBISS.SI-ID: 14392603