Dear Mohammadali M.

Cavitation is the formation of vapour cavities in a liquid – i.e. small liquid-free zones ("bubbles" or "voids") – that are the consequence of forces acting upon the liquid. It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shock wave. Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. This results in surface fatigue of the metal causing a type of wear also called "cavitation".

If the pressure of a liquid in course of its flow becomes equal to its vapour pressure at the existing temperature, then the liquid starts boiling and the pockets of vapour are formed which create vapour locks to the flow and the flow is stopped. The phenomenon is known as cavitation. To avoid cavitation, the minimum pressure in the passage of a liquid flow, should always be more than the vapour pressure of the liquid at the working temperature. In a reaction turbine, the point of minimum pressure is usually at the outlet end of the runner blades, i.e at the inlet to the draft tube. For the flow between such a point and the final discharge into the trail race (where the pressure is atmospheric),

https://www.researchgate.net/post/How_does_cavitation_happen_in_a_turbine_Is_there_any_book_referring_to_this?_tpcectx=profile_questions

https://books.google.co.in/books?id=u18FNWXnrEYC&pg=PA32&lpg=PA32&dq=steam+turbine+cavitation&source=bl&ots=fM-cvnJ6Hn&sig=GK_O6gn5NO4z0v-Ko96sgk1nDlM&hl=en&sa=X&ved=0ahUKEwjjj5HlvsDOAhUiS48KHdy1B38Q6AEIVzAH

Article CAUSE AND PREVENTION FOR STEAM TURBINE BLADE SCALING & FOULING

Thank you for your useful information. It is important for me to know how to set cavity in Fluent too. A file to  guide how to analyze  cavity on blades in Fluent