Study On The Influence Of The Variation Of Blade Curvature Radius On The Hydraulic Performance Of Centrifugal Pump Impeller

Multi-stage centrifugal pumps are widely used in industrial and agricultural production.Improving the efficiency of multi-stage centrifugal pumps is of great significance both in energy saving and emission reduction and in e enhancing the competitiveness of enterprises' products.As an important energy conversion component in the pump,the performance of the impeller directly affects the overall operation of the pump.Because the flow mechanism inside the impeller is extremely complicated,it is necessary to conduct an in-depth study on the flow mechanism in the impeller to determine the main factors affecting the hydraulic efficiency of the impeller.In this paper,the method combining theoretical analysis,numerical calculation and experiment is used.Firstly,from the theoretical point of view,accomplishing the qualitative analysis of the main factors affecting the distribution characteristics of the velocity field and pressure field in the impeller and their action methods.Secondly,combining with the results of theoretical analysis,the effect of different variation characteristics of the blade profile on the hydraulic efficiency of the impeller is discussed.And finally determining the distribution characteristics of the blade radius of curvature when the hydraulic efficiency of the impeller is high,in order to provide valuable theoretical reference and direction guidance for the optimization of the hydraulic performance of the centrifugal pump.The results show that the numerical calculation accuracy of dividing the boundary layer grid in the entire computing domain is the highest compared with that without the boundary layer grid,and the boundary layer grid is only divided in the impeller or the extrusion chamber.Compared with the steady calculation results,the unsteady calculation performance prediction curve agrees better with the experiment curve;the prediction accuracy of the DDES turbulence model on head and shaft power is significantly higher than that of the RNG k-? turbulence model.However,the efficiency in overall prediction accuracy is slightly lower than the RNG k-? turbulence model.The steady calculation of the RNG k-? turbulence model has a relatively high numerical simulation accuracy at the design flow conditions,so the subsequent research will use the RNG k-? turbulence model and the steady calculation method,and add a boundary layer grid in the full calculation domain.Through theoretical analysis of the dynamic characteristics of the fluid particles in the impeller,the effects of rotating centrifugal force,Coriolis force and curvedsurface centrifugal force on the movement characteristics of the fluid particles in the impeller are performed,and the direction of the hydraulic optimization of the impeller is proposed.The results show that the rotating centrifugal force mainly performs working on the fluid particles;the Coriolis force pulls the fluid particles from the blade pressure surface to the suction side of the blade,which will cause the flow velocity of the suction surface of the blade to be higher than the pressure surface;the curved surface centrifugal force causes the fluid particles to migrate from the suction surface of the blade to the blade pressure surface,and it also has a positive effect on improving the uniformity of the velocity distribution in the impeller.Therefore,in the process of hydraulic optimization of the impeller,appropriate control of the changing trend of the blade curvature radius along the flow direction is the key to reconcile the combined effects of Coriolis force and curved surface centrifugal force.The blade profile is an important factor which affecting the hydraulic efficiency of the impeller.Under the premise that the blade wrap angle is unchanged,by means of altering the blade inlet angle,outlet angle and the variation tendency of the grid streamline,the changing characteristics of the impeller profile along the flow direction can be controlled.Taking the blade curvature radius of the center streamline of the blade working surface as the geometric characteristic physical quantity,the effect of different changes of the blade curvature radius on the hydraulic efficiency of the impeller is systematically studied.The results show that reducing the blade curvature radius can improve the uniformity of the speed distribution in the impeller flow channel to reduce hydraulic loss,and at the same time can reduce the pressure difference between the two sides of the blade in the main working area of the impeller to reduce the shaft power,which is beneficial to improve the hydraulic efficiency of the impeller.When the blade curvature radius shows a downward trend in the flow direction near the inlet of the blade,maintaining a small value and continuously smooth changes throughout the flow interval,the flow field structure in the impeller flow channel is better,and the hydraulic efficiency of the impeller is relatively higher.The hydraulic optimization theory of the centrifugal pump impeller based on the controlling of the blade curvature radius distribution characteristics has achieved good results in engineering applications.The pump has high experimental efficiency and a wide high efficiency area.The hydraulic design is successful at one time,which also proves the reliability and feasibility of the optimization theory and its application value.