Research And Discussion On Unconventional Methods Of Impeller Cutting In The Centrifugal Pump

There is a tendency in some low specific-speed pumps to generate drooping H-Q characteristics as flow rate Q decreasing around the shut-off point. This phenomenon might result in instability when the pump working at low flow rate area. Some unconventional impeller cutting methods can improve this H-Q instability, such as removing part of the vane and impeller crown, removing a triangle or semicircular area at the vane outlet and so on. In order to remove H-Q instability, these unconventional impeller cutting methods were studied based on CFD simulation and experiments. To investigate the relationship between the geometry of impeller outlet and H-Q instability, the flow field of pump at off-design point was analyzed, typically at low flow rate area.The main research content is as flowing:(1) Searched for a wealth of literatures about centrifugal pump impeller cutting, and summarized the conventional impeller cutting method which is carried out by reducing impeller external diameter and a variety of impeller cutting laws. These works provided theory supporting for designing new unconventional impeller cutting methods.(2) The technology about studying flow field in centrifugal pump based on CFD simulation was introduced systematically, including three-dimensional modeling by Pro/E, mesh generation by Gambit and the process of Fluent setting. And then the hydraulic model of IS80-50-250single-stage and single-suction rinsing centrifugal pump was simulated by the CFD technology mentioned previously.(3) The triangle cutting, semicircular cutting and part of the vane and impeller crown cutting methods were described in detail. Performance curves of the original centrifugal pump model and all pump models modified by different unconventional impeller cutting methods were predicted based on CFD simulation results. The influence of different cutting methods with different shape and size on performance of centrifugal pump was investigated and a set of optimized cutting models to remove H-Q instability were determined at last.(4) Depending on CFD simulation results, the flow pattern of centrifugal pump at design and off-design condition was analyzed by post-processing tools of Fluent. The analysis shows that the mixing and shock losses due to unsymmetrical distribution of flow pressure and velocity at impeller inlet are important factors resulting in decreasing the shut-off head and generating H-Q instability. And modifications of impeller outlet by proper unconventional cutting methods can removal the H-Q instability effectively.(5) In order to check the reliability of CFD simulation, a group of pump performance tests about model pump and the triangle cutting method with the optimized size were carried out. The comparison shows that both of head and efficiency can be predicted based on CFD simulation with acceptable accuracy. Specifically, the head prediction error is-3.02%～1.69%, and the efficiency prediction error is1.46%-4.72%.