An energy conservative method to predict the erosive aggressiveness of collapsing cavitating structures and cavitating flows from numerical simulations

Abstract

An energy conservative method to predict the erosive aggressiveness of collapsing cavitating structures and cavitating flows from numerical simulations Schenke, Sören; van Terwisga, Tom J.C. a b s t r a c tA new technique is proposed in this study to assess the erosive aggressiveness of cavitating flows from numerical flow simulations. The technique is based on the cavitation intensity approach by Leclercq et al. (2017), predicting the instantaneous surface impact power of collapsing cavities from the potential energy hypothesis (see Hammitt, 1963;Vogel and Lauterborn, 1988). The cavitation intensity approach by Leclercq et al. (2017) is further developed and the amount of accumulated surface energy caused by the near wall collapse of idealized cavity types is verified against analytical predictions. Furthermore, two different impact power functions are introduced to compute a weighted time average of the impact power distribution caused by the cavity collapses in cavitating flows. The extreme events are emphasized to an extent specified by a single model parameter. Thus, the impact power functions provide a physical measure of the cavitating flow aggressiveness. This approach is applied to four idealized cavities, as well as to the cavitating flow around a NACA0015 hydrofoil. Areas subjected to aggressive cavity collapse events are identified and the results are compared against experimental paint test results by Van Rijsbergen et al. (2012) and the numerical erosion risk assessment by Li et al. (2014). The model is implemented as a runtime post-processing tool in the open source CFD environment OpenFOAM (2018), employing the inviscid Euler equations and mass transfer source terms to model the cavitating flow.

On the Applicability of Cavitation Erosion Risk Models With a URANS Solver

“…(23) should not be taken into account for the radiated energy. Furthermore, the effect of the pressure gradient on the energy release is depicted by the p d term, as stated by Schenke and Terwisga [41]. Thus, the local impact rate _ eðtÞ is computed in every cell as follows:…”

“…This is also depicted by the density-pressure trajectory, which should be very close to vapor pressure during phase change. On top of that, the driving pressure is practically never exactly constant in space [41]. In this study, the timeaveraged pressure field is computed, from the instantaneous pressure field p i in cavitating flow conditions, assuming this field to be the ambient pressure field driving the cavity collapses.…”

Numerical Simulation of Cavitation Erosion Aggressiveness Induced by Unsteady Cloud Cavitation

“…In order to calculate the potential power reaching a certain position j on the surface of the hydrofoil that has been induced by a collapse occurring at a given point source i on the fluid domain at instant t, the method proposed by Sören and van Terwisga [26] has been applied. For that, it has been assumed that P den (i,t) propagates circumferentially with an infinite wave speed in radial direction without energy losses and that it reaches position j at the same time t, as outlined in Figure 3.…”

“…Besides, the divergence term, ∇ • u, is actually another form of continuity equation (Equation 5) defined as ∇• = ( − ) [26]. Hence, Equation 18can be rewritten as:…”

“…Among the erosion models discussed above, the model proposed by Fortes-Patella et al [17,18] has been widely used because it has been validated by various researchers and it provides a good agreement with the experiments [23][24][25][26][27]. Another reason for its popularity is that it has also been applied to industrial and engineering cases such as marine propellers [25] and pumps [28].…”