Study on the Temporal and Spatial Evolution Mechanism of Rotating Cavitation in the First Stage Impeller of LNG Submersible Pump With Two-Stage Splitter Blades

Abstract

This study establishes a full-flow passage numerical model of an LNG submerged pump equipped with two-stage splitter blades through three-dimensional modeling. Numerical simulations validated by liquid nitrogen experiments demonstrate that at 1.4 times the design flow rate, the peak efficiency reaches 60.6%, with a maximum head of 194.93 m. The errors in head and efficiency across all operating conditions are below 4.3% and 8.3%, respectively. Cavitation inception occurs at NPSHa = 15, with a critical cavitation number of σ_cir = 0.142 (corresponding to a net positive suction head of 3.12). Before cavitation breakdown, the head increases by 4.69%. A sub-synchronous rotating cavitation phenomenon is observed under design conditions. Its evolution mechanism involves cavitation recession triggering high turbulent kinetic energy (TKE) accumulation in the blade wake region. The TKE surge induces stall and flow separation on secondary main blades, further promoting downstream cavitation volume growth. The study confirms that the TKE propagation frequency (0.227 times the rotational frequency) synchronizes with the cavitation rotation frequency, indicating a coupled evolution relationship. By analyzing the critical conditions and instability mechanisms of impeller cavitation flow, this study provides critical technical support for enhancing the operational reliability and hydraulic performance of LNG pumps.