Numerical Study On The Influence Of Tip Clearance On The Internal Of Semi Open Centrifugal Pump

In this paper,from the point of view of tip clearance,a semi open centrifugal pump in the laboratory is used as the calculation model,which is modeled by the method of computational fluid dynamics.The external characteristics of the model pump are predicted by means of ANSYS numerical simulation,and the simulation value is compared with the experimental data to verify the accuracy of the selected turbulence model and numerical simulation.On this basis,change the gap value,select 0.2mm and 1.0mm near the gap value of 0.6mm,respectively,to explore the influence of tip clearance on the flow inside the impeller,especially the tip clearance area.A cavitation model is added to analyze the mechanism of the effect between tip clearance and cavitation.Finally,pressure monitoring points are set in each area of impeller to explore the relationship between tip clearance and pressure fluctuation.The main contents and conclusions are as follows:(1)According to the given parameters of centrifugal pump,the impeller and guide vane are modeled,and then the mesh is divided and preprocessed.The number of calculation mesh is determined through the verification of mesh independence.Comparing the external characteristic data of numerical simulation with the experimental data,the error is within the acceptable range,which verifies the accuracy of the model.(2)The numerical simulation results of model pump with tip clearance of 0.6mm are analyzed.Through the analysis of the pressure field in axial direction,it can be seen that the main range of the influence of tip leakage flow on the main flow extends from the tip clearance area down to the section height of Span = 0.75,and the section height of Span = 0.85 is the main area of the influence of tip leakage flow on the main flow.Because of the influence of the boundary layer of the front cover plate,the structure of the tip clearance leakage vortex is mainly affected by the flow line released from the tip clearance height below 75% h.(3)Select the gap value equidistant,calculate the tip leakage using continuity equation,and get the positive correlation between the gap value and the leakage.With the increase of tip clearance,the head and efficiency of water pump are negatively correlated.By analyzing the streamline CP curve at 0.85 times of the section height,it can be seen that the stability of 0.2mm and 1.0mm ?Cp value of the tip clearance is poor.At the same time,considering the machining accuracy of the actual tip clearance,it is suggested that the value range of the tip clearance of the model pump is 0.3mm ~ 0.8mm.(4)The critical NPSH increases with the increase of the tip clearance,that is,the increase of the clearance value weakens the anti cavitation performance of the pump.By analyzing the cavitation performance curve and bubble volume distribution under different clearance,it is further verified that the increase of clearance value can weaken the anti cavitation ability of pump.(5)Under the same tip clearance,the frequency and amplitude of pressure fluctuation at the pressure surface,suction surface and dynamic static interface are different.The amplitude of pressure fluctuation at the leading edge of blade is significantly lower than that at the trailing edge.According to the analysis of monitoring points at the same position under different tip clearances,the amplitude of pressure fluctuation at 0.2mm is far smaller than that of other tip clearances,but with the increase of clearance value,the number of peaks and troughs of monitoring points decreases during the period of impeller rotation,that is,the disorder degree of pulsation increases.