| Compared with the traditional axial flow pump,the conveying medium of axial flow pump in loop reactor is complex polymer,such as polypropylene.And generally,there is no guide vane or straight guide vane is used in the pump.Due to the particularity of circulating medium and structure of annular axial flow pump,its internal unstable flow characteristics are strong,and the shaft power fluctuation is often large in operation.Therefore,it is of great significance to master the law of unsteady flow in annular axial flow pump for improving the reliability of pump operation.Based on the Sinopec project"Development of large petrochemical axial flow pump for polypropylene plant with an annual output of 300000 tons",the key hydraulic components of annular axial flow pump with nominal specific speed of 1000 were designed by theoretical calculation;The steady-state and unsteady three-dimensional flow field of the model pump were calculated by CFD method;The operation characteristics of saddle area,dynamic and static interference characteristics between impeller and guide vane,three-dimensional entrainment structure of tip leakage vortex and its evolution were mainly studied;At the same time,the efficiency conversion between model pump and prototype pump is studied through the energy characteristic test.The main contents and innovative achievements are as follows:1.Based on the non-linear circulation distribution and meridional velocity distribution of the impeller outlet,the impeller and guide vane are designed by streamline method,and the initial design scheme of the model pump was obtained.Taking the initial impeller as a reference,five impeller design schemes with blade angles(?_L=-4°,-2°,0°,+2°,+4°)are established.The saddle area operation characteristics are obtained by numerical calculation.It is found that when?_L=-2°,the hydraulic performance of the model pump is the best.At the same time,according to the best design scheme,the fluid structure coupling calculation of the impeller rotor system is carried out by using Workbench software to verify the reliability of the structural design,and the performance test of the model pump is carried out.The results show that the hydraulic performance of the model pump meets the design requirements.2.On the basis of the optimal design scheme(?_L=-2°),the matching relationship between impeller and guide vane with five axial gap(s=0.05D,0.075D,0.1D,0.125D,0.15D)is established.Combined with the transient variation laws of pressure fluctuation,axial force,radial force and shaft power fluctuation in the whole flow passage,the rotor-stator interference characteristic on the unstable flow in the pump was explored.The results show that:(1)The axial gap has little influence on the hydraulic performance of the pump near the rated working condition.Reducing the axial distance is beneficial to improve the hydraulic performance of the pump under the condition of large flow,but it is opposite under the condition of small flow.(2)With the decrease of axial gap,the length of trailing edge vortex and the separation range of triangular region on the suction surface of guide vane decrease.At the same time,it is also observed that under the condition of small flow rate,the reflux velocity at the hub of impeller outlet increases with the decrease of spacing.(3)Under the condition of small flow rate,the axial force,radial force and peak to peak value of shaft power are much larger than those of other working conditions.With the increase of axial gap,the main frequency of axial force fluctuation changes from double blade frequency to double blade frequency,the fluctuation of radial force decreases continuously,and the peak value of shaft power fluctuation decreases continuously,but the decreasing amplitude shows a decreasing trend.When s=0.075D,the axial force is the minimum,and when s=0.15D,the fluctuation of axial power,radial force peak value and fluctuation are the minimum.3.On the basis of not changing the diameter of impeller,five model pumps with blade tip clearance dimensions(?=0mm,0.25mm,0.5mm,1mm,2mm)were established.On the premise that the clearance cross-sectional area is same,three kinds of model pumps with tip clearance types(the clearance dimensions from leading edge to trailing edge are constant,decreasing and increasing respectively)were established.Based on the calculation of tip leakage loss,turbulent kinetic energy distribution and Q-criterion identification,the effects of tip clearance on tip separation vortices,tip leakage vortices and pressure fluctuations in the tip clearance are analyzed,and the evolution process of tip leakage vortices is explored.The results show that:(1)When??1mm,the leakage flow causes secondary leakage to the adjacent blades,and the hydraulic performance decreases obviously.The hydraulic performance of the model pump with tapered tip clearance is slightly better under large flow condition;Under the condition of small flow,the performance of the pump with conventional tip clearance is slightly better.(2)The tip leakage loss increases linearly with the increase of clearance,and decreases nonlinearly with the increase of flow rate.(3)In the tip clearance,the closer the monitoring point is to the guide vane,the higher the amplitude of the guide vane passing frequency.By increasing the flow rate,the dynamic and static interaction between impeller and guide vane can be weakened,and the amplitude of guide vane passing frequency can be reduced.(4)The Q-criterion vorticity isosurface method is used to analyze the periodic change process of tip leakage vortex.The preliminary analysis shows that the collapse of leakage vortex and the shedding of trailing edge vortex are the reasons for the pressure fluctuation amplitude at the impeller outlet flange greater than that at the hub.4.Based on the similarity principle and partial efficiency calculation theory,the least square method is used to fit the test data of model pump and solve the efficiency constant,so as to realize the parameter conversion of hydraulic characteristics of prototype pump under all working conditions.At the same time,the prototype pump is further processed and the energy characteristic test is carried out.According to the test results of the prototype pump,the hydraulic performance of the prototype pump meets the design requirements and the national standards.Comparing the test results with the formula conversion results,the overall trend of the head curve and efficiency curve is basically the same.Under the optimal conditions,the relative error of head is 2.2%,and the relative error of efficiency is 0.33%.The partial efficiency conversion method has certain reliability,which makes up for the deficiency of only considering hydraulic efficiency in the previous efficiency conversion. |
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