Research has been conducted to evaluate a technique for measuring the cavitation strength of water. The technique is based on counting cavitation events as a function of cavitation number on a standard body, thereby producing cavitation characteristic curves. It is assumed that water cavitates because of nuclei carried in the water and that the measured characteristic curves must therefore be related to the nuclei which are present. In this research it was hypothesized that the nuclei, whatever their real nature, could be represented by a distribution of equivalent gas bubbles of neutral density. The standard bodies were designed according to potential flow theory so that the bubble trajectories, along with their cavitation rates, could be calculated. By calculating cavitation characteristic curves for various bubble numbers and size distributions and comparing the calculated curves with measured curves for the same body, it was possible to infer the specifications for the equivalent bubble nuclei that were present in any test. The equivalent nuclei can be described using N, the number of cavitatable bubbles per unit volume of water (a number far smaller than the total number of nuclei per unit volume); rmax, the likeiy radius of the largest bubbles in the distribution; and a, a parameter of the exponential size distribution assumed for the bubbles. As a consequenoe, given (N,rmax,a) and an experimental realization whose flow field can be calculated by potential flow theory, it should be possible to predict incipient cavitation. The experiment devised for verifying this statement proved to be faulty, and experimental verification has not yet been accomplished. An alternative for future study has been proposed which calls for abandoning the hypothesis of equivalent bubble nuclei and determining the relative cavitation strength of water by direct comparison of a measured cavitation characteristic curve obtained on a standard body in a specific test configuration with a catalogue of such curves kept on file for a family of standard bodies.
|Original language||English (US)|
|State||Published - Sep 1973|