The tip clearance, a compact gap between the inducer blade tip and casing wall, is critical to both the liquid leakage and cavitation-induced forces of a turbopump. In this study, we numerically investigate the effect of tip clearance on the cavitation characteristics of an inducer. Six different tip clearances, 0.1, 0.3, 0.5, 1.0, 1.5, and 2 mm, namely Models A–F, were designed to evaluate the cavitation performance, cavity structure, blade loading, radial force, etc. Model D (1.0 mm) had the relatively highest head coefficient and smallest cavity area on each blade as compared to all other models. The pressure coefficient distribution and blade loading further confirmed that Model D can maintain a higher pressure head and better suppress the cavitation onset than the other models. The radial force signals in the time and frequency domains show that Model D has an intermediate force magnitude with slightly higher noises at the rotating frequency and its harmonic frequencies. Model D also has a relatively smaller vortex region and smaller vortex strength (λ2 criterion). In short, all results show that Model D is the best alternative to balance the complex interactions of the bulk flow and tip leakage flow, compromising the hydraulic head and rotating cavitation.

Rotating cavitation (RC) in inducers mainly degrades performance with unstable radial force. In this paper, the influence of step casings on cavitation performance and the instabilities of inducers were numerically investigated. Firstly, a numerical scheme was validated by means of a comparison with experimental measurements taken for an original inducer (Model O). We then performed simulations with five different step casing models (Models A–E), in which the starting locations and enlargement sizes of the step casings were altered. The interaction between tip leakage flow and main flow in the inter-blade passages was found to highly affected by cavity structure and blade loading. Considering both cavitation performance and radial force, our results suggest that Model E is an alternative improvement. In short, this study provides a standard workflow for the effective suppression of rotating cavitation in inducers by the simple adoption of the step casing configuration presented here in engineering practice.