Influence Of Geometric Parameters On External Characteristic Curve Of Pump As Turbine

Energy is the motive force to promote the development of national economy.How to rationally use the existing energy is the main problem in our today’s society.Hydraulic turbine is a device for recovering residual energy of liquid pressure.It has many advantages,such as low cost,simple structure and so on.In the chemical process industry,there are some liquid with high pressure energy,which can be recovered by hydraulic turbine.However,in the actual chemical production,the output is adjusted according to the requirements,and the flow rate of production will also change,but the pressure will generally remain unchanged due to the requirements of the production process.In order to adapt to the influence of production regulation on turbine performance in chemical process industry,it is required that the inlet and outlet pressure heads of hydraulic turbines change little with flow rate,which means the pressure head and power of hydraulic turbines change little with flow rate,and the pressure head-flow curve and power-flow curve are relatively flat,so as to ensure the production process requirements and the stable operation of hydraulic turbines.Therefore,in this paper,a single-stage single-suction centrifugal pump as turbine is selected as the research object by combining theoretical analysis with numerical simulation,in order to analyze the influence of geometric parameters on the performance of the hydraulic turbine..The main research contents and results are as follows:1.On the premise of the conservation of the velocity moment in the volute of a hydraulic turbine,the relationship between the theoretical pressure head and power of the turbine and the flow rate and the geometric parameters of the turbine is derived.Through the study of the relationship,the geometric parameters affecting the slope of the external characteristic curve of the turbine are obtained as follows: wrap angle of volute,blade outlet angle,blade outlet edge parameters and blade number.2.Choosing a low specific speed pump as turbine as the research object,13 research schemes are determined by changing the geometric parameters such as wrap angle of volute,blade outlet angle,blade outlet parameters and blade number.The 13 schemes are simulated and tested by ANSYS-Fluent software.The results show that the pressure head-flow curve and power-flow curve become flat when the wrap angle of volute is appropriately reduced and the blade outlet angle is appropriately increased.The turbine pressure head-flow curve and power-flow curve are more flat when the optimal blade outlet position and the optimal number of blades exist.The angle of volute has a significant effect on the slope of pressure head-flow curve and power-flow curve.3.By comparing the internal flow field near the high efficiency point of the turbines with the 13 model pumps,it is found that the pressure difference between inlet and outlet of the turbines increases with the increase of wrap angle of volute near the high efficiency point of the turbines,which conforms to the law that the head-flow curve and power-flow curve of the hydraulic turbines steepen with the increase of the wrap angle of volute.Internal flow field of hydraulic turbine.When the hydraulic turbine runs near the high efficiency point,the velocity in the runner is smaller and the flow is more stable.The velocity streamline at the impeller inlet is chaotic.With the increase of the number of blades,the vortex region decreases gradually,and the flow of fluid is improved.