Cavitation

Cavitation is the formation of vapor bubbles within a liquid when flow dynamics cause the local static pressure to drop below the vapor pressure. The bubbles usually last a short time, collapsing when they encounter higher pressure. Cavitation can cause noise and vibration, structural wear and damage, leading to reduced performance.

Cavitation can present problems with many products that are associated with fluid flow including:

  • Pumps (positive displacement)
  • Fuel injectors
  • Valves
  • Compressors
  • Turbochargers
  • Propellers (and other marine applications)
  • Spillways

However, cavitation can also be useful in controlled applications:

  • Ultrasonic devices (shock wave lithotripsy)
  • Cavitation jets for cleaning surfaces
  • Low drag torpedoes and marine hulls

Cavitation needs to be identified and diagnosed early in the design process to get the design right the first time. But it is usually impossible to identify cavitation during physical testing until it reaches high levels and the resulting noise and vibration become apparent. Even then, it's hard to confirm that cavitation is the root cause of the problem. Many computational fluid dynamics (CFD) software packages have difficulty in predicting cavitation because they are not able to account for the motion of structural components; are not able to couple flow analysis with other physics, which is often needed for accurate cavitation simulation; and offer no, or perhaps only a limited selection of, cavitation models. Without accurate prediction of cavitation, users cannot effectively optimize designs and set operating parameters and limits, potentially exposing their products to unexpected vibration and damage.

Pump cavitation

ANSYS Fluent simulation of oil volume in a gerotor pump showing the extent of cavitation (red) on the gear wall.

Accurate simulation of cavitation can enable your engineering team to quickly evaluate alternative product and process designs to increase efficiency, reliability, safety and durability in a competitive, time-critical environment. ANSYS CFD solutions provide the building blocks needed to accurately and quickly analyze cavitation. ANSYS dynamic or moving mesh capabilities make it easy to accurately model moving elements such as impellers or vanes that are commonly found in applications where cavitation is a concern. With ANSYS CFD solutions, you can easily predict interactions between fluids and structures, which is an important characteristic of many cavitation applications. Finally, ANSYS provides the most accurate multiphase modeling, including numerous choices of cavitation and turbulence submodels that maximize accuracy by matching the model to the application for the best fit. Cavitation is a critical computational fluid dynamics app that you have to get right.

Cavitation: A Critical App You Have to Get Right

New in ANSYS 18: Fluent accurately characterizes cavitation where multiple fluids and noncondensing gases are present

Pump designers need to accurately predict cavitation so they can define operating limits and prevent premature damage. New simulation tools are needed to accurately model cavitation in challenging operating conditions such as high pressures and multiple-fluid mixtures. ANSYS Fluent now can incorporate multiple cavitation mechanisms in a single simulation and account for noncondensable gases in liquid and their effect on cavitation using interphase species mass transfer models.

Pump cavitation prediction