| When the pump is running,the fluid causes high axial force in its axial direction,Axial force is one of the primary factors affecting the stable operation of the pump,Excessive axial force causes the bearing temperature to be too high,which could affect the normal operation of the unit and even cause serious damage.Therefore,it is extremely important to balance the axial force with a suitable balance method in pump design.The research goal is to reduce the axial force of the centrifugal pump impeller,based on the RNG k-ε turbulence model,steady calculations and full computational domain,the study was made to research the influence of impeller geometric factors such as position and methods of balance hole opening,curvature radius of front and rear shrounds of impeller and axial projected area of blade on the axial force of impeller and pump performance systematically.And on this basis,a comprehensive axial force optimization method was proposed,so as to confirm the major geometric parameters that affect axial force of the impeller,and expected to supply worthy reference to the axial force optimization direction and method on the basis of the control of impeller geometric parameters.In order to improve the comprehensive prediction accuracy of centrifugal pump hydraulic performance,this paper had done a series of studies on the selection of turbulence model,the verification of grid independence,and the selection of grid size near the wall,etc.And each part of axial forces acting on the impeller was also analyzed briefly.The results show that choosing an appropriate number of grids and grid size near the wall is beneficial to boost the numerical calculation precision,and the magnitude,direction and percentage of the axial force applied to the original impeller are analyzed by numerical calculation methods,except that the direction of the dynamic reaction force towards the back of impeller,the force of front and rear chambers and the axial force on the blades all point to the inlet of the impeller,and the force of front and rear chambers accounts for most of the total axial force of impeller,followed by the dynamic reaction force and the axial force on the blades,and the proportions of the two parts are almost the same.And the axial force is expressed in a dimensionless form for making the subsequent research results more significant universially.Guided by reducing the force of front and rear chambers to optimize the axial force of impeller,the influence of the position change of balance hole on the axial force of impeller and the performance of pump was studied systematically,the results show that the smaller the radial distance from balance hole to pump shaft is,then the lower the pressure in the rear chamber,the smaller the axial force of impeller as well,and decreasing the radial distance from the balance hole to the pump shaft benefits to reduce the axial force of impeller,compared with the original model,the axial force of the model with smallest axial force is reduced by 3.6%;the closer the balance hole is to the back of blade,then the greater the leakage of balance hole,the smaller the pressure in the rear chamber,the smaller the axial force of impeller as well,and making the position of balance hole close to the back of blade is beneficial to reduce the axial force of impeller,compared with the original model,the axial force of the model with smallest axial force is reduced by 12%,the change in the circumferential position of the balance hole has a greater impact on the pump efficiency while has a minor impact on the head;the change of the head and efficiency caused by the axial angle of balance hole is less than 1%,and the change of the axial angle of the balance hole has a small effect on the pump performance;The larger the axial angle of the balance hole is,the bigger the leakage of the balance hole,the higher the pressure in the back chamber,the greater the axial force of the impeller,and changing the axial angle of balance hole does not achieve the purpose of optimizing the axial force,the direction of the balance hole parallel to the direction of the pump shaft is still best choice.Guided by increasing the dynamic reaction force of liquid on the back shround to optimize the total axial force of impeller,the influence of the change in the curvature radius of front and rear shrounds of impeller on the dynamic reaction force,total axial force of impeller and performance of the pump was studied systematically.The results show that increasing or decreasing the curvature radius of the front and rear shrounds of impeller is beneficial to improve the pump head and efficiency,but the variation range of head and efficiency is within1%,and the change in the curvature radius of front and rear shrounds of impeller has little effect on the performance of pump;The smaller the curvature radius of the front and rear shrounds of impeller is,then the greater the dynamic reaction force,and the smaller the total axial force of impeller as well;Decreasing the curvature radius of the front and rear shrounds of impeller speeds up the variation in the direction of flow velocity in the impeller,and the angle between axial plane velocity and axial direction increases,and the dynamic reaction force of the liquid on the inner surface of shrounds increases,thus achieving the purpose of reducing the axial force of impeller,compared with the original model,the axial force of the model with smallest axial force is reduced by 3.4%.Guided by reducing the axial force on the blade to optimize the total axial force of impeller,based on the original model pump hydraulic design,the effect of axial projected area of blade on the axial force of the baldes,total axial force of impeller and the performance of pump was researched from two aspects: the inlet position of blade edge remaining unchanged and changed.The results show that reducing or increasing the axial projected area of blade changes the pump performance,but the variation range of head and efficiency both are less than 1%,the variation of the axial projected area of blade has a smaller effect on the pump performance,and the smaller the axial projected area of the blade is,then the smaller the pressure difference between the working surface and the back of the blade,the smaller the axial force on the blade,the smaller the total axial force of impeller as well;When the inlet position of blade edge changes,the variation of the axial projected area of blade has a more obvious effect on the axial force of blade and the total axial force of impeller,and the optimization result for axial force of impller is better by changing the inlet position of blade edge to reduce the axial projected area of blade,compared with the original model,the axial force of the model with smallest axial force is reduced by 4.4%.Finally,combaning the above-mentioned 4 methods of reducing the axial force of impeller,namely: decreasing the radial distance from the balance hole to the pump shaft,making the position of balance hole close to the back of blade,decreasing the curvature radius of the front and rear shrounds of impeller and reducing the axial projected area of blade,a integrated method of optimizing axial force was proposed.The results show that: the integrated optimization method has little effect on the pump performance and its axial force optimization is better compared to other 4 methods when used alone,compared with the original model,the axial force of the integrated model is reduced by 25.8%.The above research results show that the axial force optimization method based on the impeller geometric parameters control is feasible,which could offer a valuable reference to the axial force optimization of centrifugal pump. |
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