6. Cavitation

6.1 Different types of cavitation

Observations of cavitation on a scale model are only possible in clear water, hence the need to degas the circuit water for several hours at low sigma values. Stroboscopic lighting is used to freeze-frame a particular blade. As the blades scroll by, the impact of a manufacturing defect on the appearance of cavitation is revealed.

With the exception of a zone in the vicinity of the heart hill, cavitation is omnipresent in a hydraulic turbine wheel. At full load, there is outlet cavitation, which generally starts on the blading at the wheel outlet on the belt side. At partial load, vortices generated by the very negative impacts encountered at low flow rates appear in the wheel's interblade channels. At high heads (respectively...