# Optimization Study on a Novel High-Speed Oil-Free Centrifugal Water Pump with Hydrodynamic Bearings  
Rong Xue  
School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China  
Yijie Cai  
School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China  
[PERSON]  
operation of the motor. The outer surface of the motor stator is sealed by the resin. Thus, the motor cavity can be used as parts of the flow path, which greatly reduces the pump volume. The traditional volute is substituted by the stay vane and guide section accordingly. The traditional one generates an axial inflow and a radial outflow, while an axial inflow and an axial outflow are guided by the new design. Although it increases the hydraulic loss, the new design will simplify the structure and reduce the size of the pump to a great extent. Due to the advantages of the small vibration, low noise, long life, stable performance, and low wear, liquid lubricated bearings are widely researched [2; 3; 4; 5] and used. Among all liquid lubricated bearings, water-lubricated bearings are gradually employed on tangent pumps, marine centrifugal pumps, boiler feed pumps, and so on, because it is pollution-free, non-combustible, and easy to implement. The effect of the surface roughness on the performance of water-lubricated polymer bearings was previously investigated [6]. An electronic pump supported by the water-lubricated bearing appeared in the boiler feed pump of a large scale internal-combustion engine [7]. The water-lubricated bearing was popular in marine centrifugal pumps [8]. Presently, water-lubricated bearings are generally used in medium and large-scale high-speed pumps. However, the research on their application in small scale high-speed centrifugal pumps are still few. Researchers focus on the generalization and summarization of hydraulic models [9; 10], profiles optimization of hydraulic components [11; 12], and internal flow fields by CFD (Computational Fluid Dynamics) with respect to optimizing the pump flow path [13; 14; 15]. Liquid streamlines in pumps are in accordance with the blade profiles, under the constraint of the impeller and stay vane. Therefore, the matching relation between the impeller and stay vane with a different blade number has a strong effect on the hydrodynamic performance of pumps [16]. The design optimization of the impeller and the stay vane was numerically carried out by [PERSON] et al. [17] and the performance improvement was obtained for the mixed-flow pump. [PERSON] and [PERSON] [18] experimentally analyzed the influence of the blade number on the performance of an axial flow turbine. They pointed out that the increased blade number will decrease the pump efficiency because of the direction change of the relative velocity at the turbine outlet. [PERSON] et al. [19] described an optimized process of the impeller and stay vane in a reactor coolant pump with the aid of CFD tools, which provided a theoretical guide for hydraulic design. The impact of the blade number on the head and efficiency of the low specific-speed centrifugal pump was studied by [PERSON] et al. [20]. A fully three-dimensional unsteady flow behavior within the impeller and stay vane of a centrifugal pump was revealed by [PERSON] [21] through laser measurements. Although the influence of the blade number on the pump performance has been researched extensively, conclusions are not in accordance with each other because of the different structures of pumps. Therefore, the systematic design work needs to be conducted for a specific design. In this paper, a novel high-speed pump with oil-free hydrodynamic bearings was proposed. A numerical model based on a steady and incompressible flow was established and assessed by comparing with experimental data. Then, the numerical studies were carried out to observe the influence of the blade number of the impeller and the stay vane on the hydraulic performance of the high-speed pump. The internal flow behavior was obtained under different computational cases.