Velocity Dependence of Cavitation Damage : Sheet-Type Cavitation

Abstract

Experimental studies are conducted to clarify the velocity dependence of cavitation damage by sheet-type cavitation around a hemispherical cylindrical body. Erosion tests are carried out using a cavitation tunnel the test section of which has a flow velocity ranging from 35 to 50 m/s with pure aluminum specimens. The peak erosion rate varies roughly with 7.8 power of the velocity. The frequency of damaging blows in the flow velocity range of 25 to 50 m/s is also obtained by counting the number of pits on the aluminum specimen. The total pitting rate varies roughly with the 7.2th power of the flow velocity. However, the exponent of the pitting rate for large pits is approximately 8.1 to 8.7. The number of large pits increases drastically with the flow velocity. Furthermore, the relationship between the flow structure in the closure region of the main cavity and the cavitation damage is discussed and it is tentatively established that cavitation erosion is caused by the collapse of inverse U-shape vortex cavities and cloud cavitation.