New dimensionless number to predict cavitation in accelerated fluid

Abstract

Cavitation is the formation of vapour cavities in a liquid due to a local low pressure. The traditional cavitation number is used to predict the occurrence of cavitation in liquid flows through devices such as pumps, propellers or dam spillways. However this number can only be applied when cavitation is produced by changes of dynamic and static pressure in a liquid flow. There are other means to produce cavitation where the traditional cavitation number cannot be applied. The purpose of this research is to formulate a new dimensionless number valid to predict cavitation in some scenarios where the traditional cavitation number fails. The “tube-arrest” method produces cavitation by subjecting a column of liquid to a high acceleration without the need of any velocity between the liquid and the tube. In this scenario the traditional number is not useful due to the low values of relative velocity between liquid and walls. However the dimensionless number reported here predicts accurately the occurrence of cavitation in the “tube-arrest” method, as it is shown by Finite Element Method analysis. There is another scenario where the dimensionless number is tested successfully that is the bulk of a liquid downstream of a closing valve. A systematic comparison between the values of the dimensionless number and the occurrence of cavitation predicted by the FEM analysis is given. On the other hand the values of the traditional cavitation number are calculated and it is shown that these values are meaningless in these scenarios. In contrast, the agreement between the prediction of the dimensionless number and the simulations is excellent. It is concluded that the new dimensionless number predicts cavitation in scenarios where the traditional number is meaningless. It can also be used for a better design of experiments with the “tube-arrest” method as a practical application.