THE RELATION BETWEEN THE NUCLEI POPULATION AND THE CAVITATION EVENT RATE

Simultaneous measurements were made of the cavitation event rates on a Schiebe body and the nuclei number dis-tributions in the oncoming stream in the Low Turbulence Water Tunnel at Caltech. Cavitation inception occurred at an average cavitation number of 0.57. Cavitation event rates increased dramatically as the cavitation number was de-creased. It was also found that both the magnitude and the shape of the nuclei distribution changed substantially with the operating condition. These changes had very strong ef-fect on the event rate and therefore on cavitation inception number based on a fixed event rate. At the same cavita-tion number, the changes in the event rate due to different free stream nuclei populations can be as much as a decade. The changes in the shape of the nuclei distribution occurred mostly in the nuclei size range above 15 pm. The nuclei concentration tended to increase as cavitation number was decreased. And the cavitation event rate increased with the free stream nuclei concentration. The measured nuclei density distributions are used in an analytical model which attempts to correlate the event rate with the nuclei population. The predicted event rates are compared with those observed experimentally.