Search

A novel cavitation erosion risk model, developed by Schenke et al. ["On the relevance of kinematics for cavitation implosion loads," Phys. Fluids 31, 052102 (2019)], is applied to compute the cavitation implosion loads. The instantaneous energy balance during the collapse of cavitating structures is considered, where the initial potential energy is first converted into collapse-induced kinetic energy, before it is radiated to the surrounding surface at the final stage of the collapse. In this study, we focus on assessing the cavitation development and the risk of erosion on the blades of propellers operating behind a Ro–Ro container vessel. The presence of the hull contributes to the non-uniformity of the inflow. The consequent variation in velocities and angles of attack leads to the amplification of the cavitation dynamics, especially when the blade passes through the top position. Two designs are investigated that experience cavitation erosion on the pressure side. A statistical filter is used to attenuate low-amplitude implosion loads and identify the extreme events on the blade. The results show a very good correlation with the position of the actual erosion damage on the real propeller blades. [ABSTRACT FROM AUTHOR]

In the maritime industry, cavitation erosion prediction becomes more and more critical, as the requirements for more efficient propellers increase. Model testing is yet the most typical way a propeller designer can, nowadays, get an estimation of the erosion risk on the propeller blades. However, cavitation erosion prediction using computational fluid dynamics (CFD) can possibly provide more information than a model test. In the present work, we review erosion risk models that can be used in conjunction with a multiphase unsteady Reynolds-averaged Navier-Stokes (URANS) solver. Three different approaches have been evaluated, and we conclude that the energy balance approach, where it is assumed that the potential energy contained in a vapor structure is proportional to the volume of the structure, and the pressure difference between the surrounding pressure and the pressure within the structure, provides the best framework for erosion risk assessment. Based on this framework, the model used in this study is tested on the Delft Twist 11 hydrofoil, using a URANS method, and is validated against experimental observations. The predicted impact distribution agrees well with the damage pattern obtained from paint test. The model shows great potential for future use. Nevertheless, it should further be validated against full scale data, followed by an extended investigation on the effect of the driving pressure that leads to the collapse. [ABSTRACT FROM AUTHOR]

Highlights • A method to assess the aggressiveness of cavitating flows with CFD is developed. • The energy balance of cavity energy conversion into impact power is investigated. • The driving pressure distribution plays a major role in this energy conversion. • It is crucial to know the sensitivity of a material to isolated extreme impacts. Abstract A 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. [ABSTRACT FROM AUTHOR]

Propeller cavitation erosion prediction at an early design stage is becoming more and more important since it is one of the key constraints in the search for maximum propeller efficiency. Despite the experience from model tests, cavitation erosion research on actual ship scale is very limited. In this study, an attempt is made to assess the erosion risk on the blades of a full-scale steerable thruster of a tug boat. Pressure side cavitation was detected on board for three different propeller designs. For the first time, a cavitation erosion analysis is performed on ship-scale, using a rigorous potential energy approach, which accounts for the focusing of the potential energy at the collapse center during the cavity collapse. A full sensitivity study has been performed for the blade surface accumulated energy. The erosion model shows the erosion risk for different propeller designs applied on the vessel, and different operating conditions, by looking at the surface specific energy on the blade. The erosion analysis shows locations of high erosion risk that show a good resemblance with the actual damage locations on the real blades. • Potential energy approach for the energy cascade of collapsing cavities. • Focusing of potential energy to the collapse center. • Solid angle is used for energy projection to the surface. • Sensitivity study of the surface accumulated energy on the propeller blade. • Comparison of blade impact distribution with actual damage on the real blades. [ABSTRACT FROM AUTHOR]