Numerical Analysis of Suppression Effect of Asymmetric Slit on Cavitation Instabilities in Cascade

In this study, numerical analysis is carried out around the cyclic flat-plate cascade with symmetric and asymmetric slit, so as to examine the suppressing or controlling effect of the slit on cavitation instabilities such as cavitation oscillation (CO) which resembles cavitation surge, and rotating cavitation. These instabilities cause various problems for the turbomachinery, for example, rotating cavitation causes an asynchronous shaft vibration, and CO causes an oscillation of column of working fluid as a result of the resonance phenomenon of the system. In liquid propellant rocket engine, suppression device for these instabilities bring increase in cost of the launch. Therefore, it is thought that to develop effective suppression technique is important for turbopumps. Especially, in this paper, two types of the flat-plate three blades cascade which have symmetric slit on each blade and three types of the cascade which have asymmetric slit were analyzed, and the results are compared with those of cascade without slit. As a result, the CO is perfectly suppressed in both of two types cascade with asymmetric slit. Also, other examined cascades have suppression effect of CO These results indicate the possibility of suppressing cavitation instabilities in actual inducers or controlling the type of the cavitation instabilities by the arrangement of the slit. Moreover, the head performance is equal or slightly increased by arranging slit.