Research On The Hydraulic Performance Optimization Of A Centrifugal Pump Impeller Based On The Passage Area Gradient Control

The change of any geometric parameters of the impeller is essentially the change of the passage area,and the change of the passage area directly affects the distribution of the velocity field and pressure field,and ultimately affects the hydraulic performance of the impeller.Therefore,in this paper,the passage of the impeller is taken as the starting point.Based on the global structured grid,the SST k-ωturbulence model is adopted to analyze the influence of different variation laws of the passage on the hydraulic performance of the impeller through steady numerical simulation,and the change characteristics of the passage and area gradient are determined when the impeller has the highest hydraulic efficiency.Then,on this basis,the passage area and area gradient are controlled,and the influence of the inlet and outlet area of the passage and their cooperative changes on the hydraulic performance of the impeller is studied.The hydraulic optimization method of the centrifugal pump impeller with the area gradient as the control parameter is determined,in order to provide new theoretical guidance and method reference for the hydraulic performance optimization of the impeller.Starting from the change rule of controlling the passage area of the impeller,the influence of the change of geometrical parameters such as the position of blade inlet edge,inlet angle,blade envelope angle and outlet angle on the passage area of the impeller was firstly studied.Then,the blade envelope angle was selected as the geometric variable through comprehensive consideration.Under the premise that the inlet and outlet area of the impeller passage remained unchanged,The influence of different passage area variation laws on the hydraulic performance of the impeller was studied,and the characteristics of passage area and area gradient along the flow direction were determined when the impeller hydraulic efficiency was optimal.The results show that moving the blade inlet edge forward or decreasing the blade envelope angle can increase the passage of the passage as a whole,while increasing the blade inlet angle or decreasing the blade outlet angle can increase the passage of the passage and reduce the passage of the exit.When the area gradient of the impeller passage decreases rapidly along the flow direction,the hydraulic efficiency of the impeller is relatively high.Changing the passage area of the impeller along the flow direction has little influence on the velocity field in the impeller,but has great influence on the pressure field.It can improve the work capacity within the effective passage interval and reduce the idle work consumption outside the effective passage interval,which is the fundamental reason for improving the hydraulic efficiency of the impeller when the passage area meets the specific change law.In order to further study the influence of the changes of inlet and outlet area on the hydraulic performance of the impeller,12 groups of schemes with different inlet and outlet area or area gradient variation rules were designed on the basis of the benchmark scheme,on the premise of keeping the overall trend of decreasing passage gradient along the flow direction.The influence of inlet and outlet area and area gradient on hydraulic performance of impeller was discussed.The results show that the hydraulic efficiency of the impeller decreases if the area gradient at the throat of the passage inlet is too large or too small.When the area gradient at the throat of the passage inlet is about 2 mm,the impeller has a relatively high hydraulic efficiency.Even if the overall trend of the area gradient along the flow direction is reduced,the hydraulic efficiency of the impeller will reach a higher level only when the trend of uniform or rapid decline is presented.And the faster the rate of the area gradient reduction,the higher the hydraulic efficiency of the impeller will be.The change of inlet and outlet area in a limited range has little effect on the hydraulic efficiency of impeller.The influence of inlet and outlet area on velocity vector field structure in impeller is not obvious,but the influence on pressure field is obvious.When the area gradient decreases at first fast and then slowly along the flow direction,the pressure difference on both sides of the blade can be significantly reduced,which is beneficial to reducing shaft power and improving hydraulic efficiency.When the variation characteristics of the gradient of the impeller passage area are basically consistent,the synergistic variation of the inlet and outlet area determines the conveyance capacity in the whole passage,and the conveyance capacity will also affect the hydraulic performance of the impeller.The results show that the hydraulic performance of the impeller is significantly affected by the conveyance capacity in the small flow condition area.The weaker the conveyance capacity is,the higher the hydraulic efficiency of the impeller is.However,the influence is relatively small in the designed flow condition point and the large flow condition area.At the designed flow condition point,the optimal conveyance capacity in the passage can make the hydraulic efficiency of the impeller reach the highest value,but too large or too small conveyance capacity will make the hydraulic efficiency of the impeller decreased.A set of comprehensive optimization schemes were designed based on the aforementioned researches on hydraulic optimization of impeller.Numerical simulation and performance prediction were carried out under the designed flow condition,and the hydraulic optimization method of centrifugal pump impeller with area gradient as the control parameter was determined.The results show that the hydraulic efficiency of the impeller can be maintained at a high level when the area gradient at the inlet throat of the impeller is about 2 mm and the area gradient decreases rapidly and then slowly along the flow direction.In the hydraulic optimization of the impeller,the optimal value of the area gradient at the inlet throat can be first found when the trend curve of the passage area is convex,and then the overall control of the passage area gradient can be carried out.Finally,the conveyance capacity suitable for the flow condition point can be found to obtain the optimization scheme with relatively high hydraulic efficiency of the impeller.In order to further verify the above research conclusions,two sets of impeller schemes with different area variation characteristics were designed with a certain type of deep well pump as an example,and tests were carried out under the same condition.The results show that when the variation law of the area gradient of the flow passage basically conforms to the basic characteristics of the high efficiency impeller mentioned above,the test efficiency of the pump under the design flow condition point is extra 1.36 percentage points higher,which verifies the reliability and feasibility of the research conclusions in this paper,and shows that the adoption of the area gradient concept can clarify the direction of hydraulic optimization and improve the quality of product design.