Generality of rotating partial cavitation in two-dimensional cascades

Abstract

Numerical simulations of 2-dimensional (2D) unsteady cavitating flows were carried out under various conditions of the number of blades, incidence angles and cavitation numbers. When the incidence angle increased or the cavitation number decreased, the steady balanced cavitation transited to unsteady and non-uniform patterns. Typical patterns reported in the previous studies such as rotating, asymmetric and alternating for 3- and 4-blades were successfully reproduced. In this study, cascades of the larger number of blades were dealt with to consider the generality of unsteadiness by reducing the influence of periodicity. The cavitation is basically triggered in the backward next section. However, the period of time for growing causes complexity in the discrimination of propagation. In most cases of rotating partial cavitation, except for 4-blades, the cavity develops in the second passage of backward direction after the decay of largest cavity. In case of many blades, multiple cavities rotate simultaneously and the particular patterns observed in cascades of small even numbers of blades attenuate.