Abstract
A numerical investigation of the erosion aggressiveness of leading edge unsteady cloud cavitation based on the energy balance approach has been carried out to ascertain the main damaging mechanisms and the influence of the free stream flow velocity. A systematic approach has permitted the determination of the influence of several parameters on the spatial and temporal distribution of the erosion results comprising the selection of the cavitation model and the collapse driving pressure. In particular, the Zwart, Sauer and Kunz cavitation models have been compared as well as the use of instantaneous versus average pressure values. The numerical results have been compared against a series of experimental results obtained from pitting tests on copper and stainless steel specimens. Several cavitation erosion indicators have been defined and their accuracy to predict the experimental observations has been assessed and confirmed when using a material-dependent damaging threshold level. In summary, the use of the average pressure levels during a sufficient number of simulated shedding cycles combined with the Sauer cavitation model are the recommended parameters to achieve reliable results that reproduce the main erosion mechanisms found in cloud cavitation. Moreover, the proposed erosion indicators follow a power law as a function of the free stream flow velocity with exponents ranging from 3 to 5 depending on their definition.
Highlights
Cavitation is an unique phenomenon in the field of hydrodynamics that occurs when the local pressure in a liquid drops below a critical value, usually close to the vapor pressure, and results in the development of various types of vapor structures such as attached cavities, travelling bubbles, vortical cavities and bubble clouds [1]
In the previous section it has been mentioned that the choice of the cavitation model and the definition of pd in Equation (20) might bring some uncertainty to the calculation of Pden and that this can lead to different estimates of Pload on the hydrofoil wall
All the models demonstrate a good performance in capturing the cloud cavitation dynamic behavior
Summary
Cavitation is an unique phenomenon in the field of hydrodynamics that occurs when the local pressure in a liquid drops below a critical value, usually close to the vapor pressure, and results in the development of various types of vapor structures such as attached cavities, travelling bubbles, vortical cavities and bubble clouds [1]. The third approach, developed by Schmidt et al, [12,13], consists of predicting the impact load spectra of a cavitating flow This method, considers the two-phase flow as homogeneous, compressible and inviscid, and it resolves the collapse-induced pressure waves to determine the spectrum of collapse events in the fluid domain. Peters et al [22] calculated the erosion potential of a cavitating flow based the accumulation of the dimensionless intensity coefficient, defined by the ratio of the jet velocity to a threshold velocity value, on every element face along the total calculation time The advantage of these approaches is that there are no critical requirements regarding the cell size and the time step and the calculation time becomes more reasonable than for instance the methods included in the third approach. The influence of the free stream velocity and the dynamic behavior of the cavitation on the estimated erosion power has been estimated based on the collapse efficiency
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