Study On The Performance Of Mixed Flow Pump As Turbine

The construction of large-scale hydropower stations requires large-scale dam structure,high construction cost and long recovery period.Dam storage reservoirs may overwhelm huge valuable agricultural lands.Without such problems,small hydropower stations can provide decentralized power generation.Especially in remote rural and hilly areas,small hydropower stations are more suitable for the development.For small hydropower stations,it is simple and feasible to use pump reverse operation as turbine for power generation.Centrifugal pump reversal as turbine is mainly used for small flow and high head conditions,and mixed flow pump as turbine is used for larger flow and low head conditions.At present,domestic and foreign scholars rarely study mixed flow pump as turbine.In this paper,the prototype of the mixed flow pump as turbine is studied.The external characteristics,internal flow state and efficient design of the mixed flow pump as turbine are analyzed by using numerical simulation,experimental comparison and relevant theories.In addition,the characteristics of the mixed flow pump are compared when medium is 5% sediment water or fresh water.The main research contents and achievements of this subject are as follows:1.The external characteristics of a mixed flow pump with specific speed of 249 and the reverse operation as turbine conditions were studied by numerical simulation and experimental method.It was found that the mixed flow pump as turbine ran well in the large flow area,and the running range was wide.The efficiency of the mixed flow pump as turbine did not drop rapidly when the system flow reduced.In the pump conditions,the efficiency of the mixed flow pump decreased rapidly.At the same time,the numerical simulation method of the mixed flow pump as turbine was obtained accurately,which laid the foundation for the further study of the mixed flow pump as turbine.2.The blade of a mixed flow pump with specific speed of 249 is designed improvably based on BladeGen software.The effect of the mixed flow pump as turbine for changing impeller wrap angle,blade number and impeller diameter was studied by numerical simulation.The performance curve,the internal flow field and the hydraulic loss of the mixed flow pump as turbine were obtained.Through analyzing the influence of the main geometric parameters of the impeller on the turbine performance of the mixed flow pump as turbine,some guidance will provide for practical engineering.3.For the actual situation of small hydropower stream water containing sediment,the effect on external characteristics and the distribution of internal flow field of the mixed flow pump with 5% sediment water and fresh water was researched respectively based on the theory of solid-liquid two-phase flow.It was found that,under the highest efficiency point flow of medium with fresh water,the volume concentration of the sand on the inner surface of the impeller front cover was higher than the rear cover when the mixed flow pump as turbine operated at medium with 5% sediment water.Therefore,for the inner surface of the impeller front cover,the head area of the blade near the back should focus on how to prevent the sand from abrasing these parts.The volume concentration of the cross section of the volute after the sixth section did not change significantly compared with the inlet concentration,but the concentration of first to fifth section was significantly increased.In conclusion,considering the anti-erosion in the volute,the concentration of first to fifth section should be mainly considered,and the anti-erosion ability near the cross section of the volute should be considered preferentially.It will provide a certain reference to the design of the impeller and volute of the mixed flow pump as turbine,with a certain degree of innovation.