Abstract
Cavitation is an inevitable phenomenon that occurs when improvements such as performance enhancement and weight reduction are made to the turbopump in liquid-propellant rocket engines. Unsteady cavitation may cause oscillations (cavitation instabilities) in the turbopump. Accurate prediction and efficient suppression of cavitation instabilities are important for designing turbopumps. We performed a numerical simulation of the unsteady cavitation in tandem cascades and compared the results with those obtained for a single-stage cascade. The type of cavitation instability could be controlled by changing the front- and rear-blade chord lengths. When the clearance gap between the front and rear blades was located near the cascade throat entrance, rotating-stall conditions could be easily achieved, even at high flow rates. Cavitation surge and super-synchronous and sub-synchronous rotating cavitations were suppressed when the clearance gap was located at 40% of the total chord length. When the clearance gap was located inside the cascade throat, cavitation reached a steady state at the σ value where the cavity length equaled the front-blade length; then, cavitation instabilities and unsteady cavitation were suppressed in the low-σ region. When the clearance gap was located at 80% of the total chord length, cavitation surge was completely suppressed, although rotating cavitation occurred over a larger region.
