Investigations on the Energy Characteristics and Internal Flow Dynamics of a Mixed-Flow Pump Considering of Inlet Pre-Rotation at Off-Rated Flow Conditions

In the industrial sphere, mixed-flow centrifugal pumps are widely used to convey acids, alkalis, brines, petroleum and other media. Their performance has a significant impact on the production efficiency of industrial systems. This paper presents an analysis of the influence of positive pre-rotation on the hydraulic performance and energy conversion characteristics of mixed flow pumps under off-rated flow conditions. The accuracy of the numerical methods adopted in this study was validated by experiments, with less than 5% error observed in head and efficiency between the experimental and numerical results at rated flow condition. The influence of positive pre-rotation on the pump's performance was found to be contingent upon the prevailing flow conditions. Under part-load flow conditions, positive pre-rotation improved the match between the medium inlet angle and blade inlet angle, leading to a reduction of the high vorticity area near the blade inlet, and consequently an improvement of hydraulic performance. However, under overload flow conditions, positive pre-rotation causes a further increment in the difference between the media inlet angle and the blade inlet angle. An increase in the secondary flow intensity within the impeller is induced, which leads to flow instability and ultimately to significant energy losses. These findings contribute to the theoretical basis for the prediction of mixed flow pump performance and operational stability improvement under off-rated flow conditions.