Cavitation in Hydraulic Machines: Measurement, Numerical Simulation and Damage Patterns

Cavitation is a phenomenon that occurs in liquid media when the pressure drops below the vapor pressure. Cavitation is accompanied by damage when the imploding vapor bubbles implode in the vicinity of components. Cavitation is known in all hydraulic machines, be it a pump or a turbine, and it can occur within all components that are flowed through and have a low-pressure side or area. In the last 100 years, a lot has been done to understand the damage caused by cavitation, and cavitation has been classified within the entire range of component-damaging mechanisms. Nevertheless, users are now interested in the behavior of different machine types and different specific speeds and need information for a particular installation situation, while hydraulic developers are interested in a methodology for the rapid assessment of CFD results. This paper presents examples of damage to all kinds of hydraulic machines as well as numerical simulations of cavitation. Cross-comparisons between single-phase numerical calculations are realized with the histogram method, and multiphase calculations are carried out and then compared with test rig investigations. Often, it is not possible or economically feasible to completely avoid cavitation. With the help of dimensionless values and the assumption of complete cavitation, a generally valid physical limit curve can be specified for turbines.