Numerical analysis about suppression effect of tandem cascade on cavitation instabilities

The occurrence of cavitation instabilities such as cavitation surge and rotating cavitation causes various problems to turbomachinery. In this study, several kinds of tandem cascade arrangements (cascade with a slit) are analyzed in terms of suppression of cavitation instabilities and then their effects are clarified numerically. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve the above-mentioned flowfields. The hydrofoil geometry is a flat plate with no thickness, and the cascade pitch/chord ratio is 0.5 and a stagger angle is 75 deg. with cyclic boundary condition every three cascade passages. As a result of analyses, It is confirmed that cavitation instabilities are suppressed in all types of tandem cascades. At the same time, when a slit position is changed, there are some differences about the flow around a slit, the length of sheet cavities arising from front blade, and pressurized characteristics. It is discussed in detail how these differences affect a cavitating flow and suppression on cavitation instabilities.