Multi-objective Optimizaton And Turbulence Simulation Of Low Specific Speed Centrifugal Pump

Low specific speed centrifugal pumps are widely used under operating conditions of low flow rate and high delivery head. But since the traditional velocity modulus design method can not be suitably applied to this range completely, low specific speed centrifugal pump always present deficiencies such as inefficiency, instability operating condition and so on. For the purpose of im-proving the performance and stability of low specific speed centrifugal pumps, this paper adopts a vertical type pipeline pump of 17 specific speed as a typical case and then conducts relevan-t research works about the CFD numerical simulation, the modification and the multi-objective optimization of low specific speed centrifugal pumps.Firstly, aiming at raising the efficiency of this low specific speed pipeline pump, several mod-ifications are done, namely, the redesign of volute, the adding of offset splitters. From numerical simulation results we may find that the new rectangular volute fixes the mismatching of stator and rotor and reduces the obvious static pressure drop near the interface between the impeller and the volute; the new volute suppresses the emergence and evolution of wake structure and alleviates the axial swirl caused by the inertia; the final trim of impeller raises the hydraulic efficiency of pump while reduces the disk friction. The experiment outcome shows that in all the flux points, the en-ergy consumption of modified pump has decreased about 2kW and the total efficiency of modified pump has increased 4%.Secondly, toward improving the performance of low specific speed centrifugal pump further, a multi-objective optimization system of impeller shape is developed. Its two objective functions are the difference between the static pressure in the pump inlet and the minimum static pressure in the impeller, the weighted sum of the deviation of local Euler head distribution curve to its ideal state and the ratio of torque exerted on the casing to the head, respectively. Five modules-(1) parametric geometrical representation of impeller shape, (2) generation of initial samples based on the Design of Experiment method, (3) automation of mesh generation and CFD numerical simu-lation, (4) approximation model of a two-layer feed-forward artificial neural network trained by back-propagation algorithm, (5) the kernel module of global evolutionary optimization algorithm, are developed to consist the whole multi-objective optimization system. The final optimal pump obtained by this system not only proves its priority in the anti-cavitation ability and hydraulic ef-ficiency compared to the modified pump, but also eliminate or suppress a lot of unwanted flow structures.Lastly, in order to have a deeper insight in the numerical simulation method of internal flow of low specific speed centrifugal pump, a new partially-averaged Realizable k-ε two-equation tur-bulence model is deduced. It is realized by the User Defined Functions on the Fluent software platform and utilized in the calculation of internal flow of aforementioned modified pump. The influence of grid amount is investigated and computation results of two turbulence models are con-trasted. This also can be treated as the supplementary description about the rationality of CFD numerical simulation and whether the accuracy standard of industrial application is fulfilled.This paper may provide a reference for the numerical simulation of complex internal flow of low specific speed centrifugal pump and the optimization design of flow passage components.