SCALING OF CAVITATION DAMAGE

This investigation has focused on the initial stages of cavitation erosion using a ductile material in a flowing system employing water as the working fluid. The test models were 0.25-in. (0.635-cm)-diam zero-caliber ogives made of pure annealed aluminum. The damage was in the form of small round depressions in the model surface. In the formation of these pits, there was no material removal. For a range of velocities from 49 to 195 fps (14.9 to 59.3 m/sec), the pitting rate increased by approximately the sixth power of velocity. The average volume of the cavitation damage pits increased by the fifth power of velocity. A relationship between the volume of a pit and the absorbed bubble collapse energy was developed. The rate of total bubble collapse energy absorbed by the model then increases by the eleventh power of velocity. A plot of the distribution of absorbed collapse energies was generated for three flow conditions. The effect of cavitation number and air content of the working fluid were also major areas of investigation. A high-speed motion-picture study of cavity dynamics was undertaken to understand better some of the processes involved in cavitation damage. Lastly, the results of this study were compared with those of previous investigations of cavitation erosion.