Being among a vast amount types of fluid machinery, centrifugal pumps play an essential role not only in industrial field but also in several areas such as civil applications, agriculture, and marine transportation. Because of possessing a series of advantages over the remaining types of pump, centrifugal pumps increasingly contribute in thousands applications of our daily life. They have a simple structure with few parts so it is really easy to operate, maintain and repair if necessary. Due to their compactness, more weight and space are saved especially in high demand working environments like merchant ships, or passenger ships. Besides, centrifugal pumps are capable to operate at high speed, can be directly connected with the electrical motor and steam turbine. They are also able to deal with a wide range of flow rate.
Nowadays, with the aid of Computational Fluid Dynamics method, the design and manufacture process of centrifugal pump are significantly shorten and improved. The trial-and-error process with a series of testing and making model is no longer a challenge, instead engineers with the assist of powerful tools are able to analyse performance of the pump with various geometries and parameters in such a short time compared to traditional method. High requirements in designing the pump to obtain higher efficiency, longer life-span, and better performance in cavity condition could raise more hardship for manufacturers. Therefore, it is essential for designers and engineers to acquire a comprehensive understanding of complicated internal flow as well as velocity and pressure field within fluid's working region in centrifugal pump so as to further improve pump performance, and shorten manufacture time. For that reason, this research is conducted and focuses on simulating and visualization flow field characteristic inside a centrifugal pump, which is installed on board a training ship and served as a general seawater cooling pump, by using numerical CFD tool. The 3D numerical analysis is carried out by addressing Reynolds Average Navier-Stock code with a Shear Stress Transport (SST) turbulence model, accounting for volumetric head loss at impeller wear ring and friction head loss due to rough wall at suction, impeller, and discharge areas. The pump's performance at designed and off-designed conditions is thoroughly investigated with steady analyses. A comparison between numerical and experimental results is executed, giving a good agreement with small discrepancy. The complex internal flows of pump can be fully simulated as smooth streamline along with impeller passage. Moreover, velocity and pressure distribution are well predicted through ANSYS CFX.
The second topic is to analyze the effects of the shape and structure of suction part on the pre-swirl vertexes formation as well as on the pump characteristics. For this purpose, three different geometries of suction domain are built and simulated at wide range of flow rate. Vectors of velocity and total pressure at several planes at suction parts are plotted to compare in order to choose the best geometry of suction shape.
Finally, a study in the pump working in cavitation condition is presented. A cavitation model is applied into the simulations for pump performance including pump head and efficiency, NPSH available at different flow rate. The bubbles formation with the reduction of suction pressure is illustrated, cavity areas at impeller eye and at the blades are also visualized clearly. Moreover, blades loading chart at 3 values of flow rate are displayed.