3-D Hydraulic Design And Numerical Simulation Of High Specific Speed Volute Mixed-flow Pump

Mixed-flow pumps are widely used in many fields of national economy due to their advantages such as moderate head, large flow rate, extensive applications and so on. However, the hydraulic design of mixed-flow pumps is still no mature theoretical system compared with the centrifugal pumps and axial flow pumps. Especially research word on the high specific speed mixed-flow pump is so little that reliable hydraulic models are lack. The volute mixed-flow pumps have such advantages as shorter axial length and more stable operating conditions than the mixed-flow pumps with guide vanes. So it is essential to investigate the hydraulic design of high specific speed volute mixed-flow pumps. The traditional hydraulic design methods of mixed flow pumps are usually based on one-dimensional flow theory of centrifugal pumps or singularity design method and lift design method of axial flow pumps. To use these methods successfully not only designers should have enough experience, but also much time and money are necessary to test and modify the pumps repeatedly.To meet the engineering requirement, this paper applied quasi-orthogonal surfaces method of three dimensional flow theory and developed volute mixed-flow pump with specific speed of 603. For the internal flow field and its pressure fluctuation characteristics and operating stability, three dimensional steady and unsteady simulations were applied to the new designed pump. The main research contents are as follows:1. To explore the direct problem method of the impeller flow field, velocity gradient equations based on three motion equation and one continuity equation were established by quasi-orthogonal surface three-dimensional flow calculation. The velocity gradient equations were decomposed along three directions to calculate the fluid particles velocity.2. The impeller basic geometry and axial projection were determined through speed coefficient method. Integrals of the blade profile equation was done with the “S” type velocity moment distribution and the impeller initial design was completed. The codes based on MATLAB software were programmed to do iterative calculations of direct and inverse problem for the initial impeller, and the final design of the impeller was finished.3. Pro/Engineer software was used to set up the solid model of the mixed-flow pump including impeller, volute, inlet and outlet nozzles. The model was imported into ICEM software to obtain the grids. Then three-dimensional steady numerical simulations under different operating conditions were done with CFX software, and the pump characteristics were analyzed.4. Monitoring points were arranged in pump internal flow channels. Three-dimensional unsteady simulations were done with steady simulation results under design condition as the initial condition. The pressure fluctuation characteristics of the internal flow fields through time domains and frequency domains were got.The results are as follows:1. According to the streamline distribution and static pressure distribution of the steady simulations, streamlines are smooth and the static pressure distribution is homogeneous. The internal flow fields are steady under the design condition and partload conditions. Compared with the prototype pump, efficiency of the new pump has increased under the design condition.2. “S” type velocity moment distribution is suitable for the hydraulic design of high specific speed volute mixed-flow pump. This has laid a solid foundation for later design of series of high specific speed volute mixed-flow pump.3. From the pressure fluctuation characteristics through unsteady simulations, in the impeller, the flow fields are complicated and are influenced by both shaft frequency and blade frequency. And in the volute, blade frequency is dominant and pressure fluctuation is stable and cyclical. The amplitude decreases gradually from volute tongue to volute outlet and along the radial direction.4. This paper has applied quasi-orthogonal surfaces method of three dimensional flow theory to design high specific speed volute mixed-flow pump. The simulation results indicates that this method makes the pump internal flow fields closer to the reality. And it can realize the stable operating requirement for high specific speed volute mixed-flow pump.