Fluid-solid Coupling Characteristics Study Of An Axial Fan With Abnormal Blade Under Rotating Stall Conditions

Axial fan is one of the most important axial-flow booster impeller machines in power station.Adjustable axial fan has been widely used because of its high efficiency,stable operation and large capacity under different working conditions.The complexity and variability of power plant operating conditions often lead to many problems in the fan,and in the process of adjusting the installation angle of the moving blade in large flow condition,the fan often has one or more installation angle drift,which leads to the asynchronous adjustment of the moving blade,thus affecting the performance and efficiency of the axial fan.The operation practice shows that the abnormal deflection of the moving blade will affect the stall characteristics of the fan in varying degrees,while the fan running in stall state will cause cracks,wear and even fracture of the blade.Therefore,it is important to analyze the fluid-solid coupling characteristics of the fan with abnormal blades at stall condition.In this paper,the axial fan of power station is taken as the research object.We give a stall simulation research on normal axial fan and abnormal axial fan which two moving blades with abnormal deflection angles of-9°、-+9°、+9°and +-9°.The simulation results show that the stall cell around half of the runner is generated in the normal impeller and the abnormal impeller at the rotating stall condition.The static pressure distribution is obviously uneven,and the negative pressure region is found in the flow channel of the stall cell.The backflow in the channel of normal impeller and abnormal impeller begins at the suction surface,flows to the pressure surface,and finally returns to the suction surface.Based on the flow field simulation data,unidirectional fluid-solid coupling of normal impeller and abnormal impeller is studied.The results show that the abnormal deflection blade has a great influence on the static characteristics of the impeller,the maximum deformation and maximum stress of impeller are increased to varying degrees due to the existence of abnormal blades in-9°、-+9°、+9°and +-9°.Compared with the abnormal blade with negative deflection,the forward deflection of the abnormal blade increases the risk of impeller fracture and deformation.The abnormal deflection blade has little influence on the dynamic characteristics of the impeller,and the natural frequencies and vibration modes of the impeller are approximately the same,and the maximum total deformation occurs near the blade top.Through the frequency domain analysis,it is found that the main exciting force frequency in the full rotating stall condition is mainly stall frequency,and the stall frequency of each abnormal impeller is approximately the same as that of the normal impeller.According to the formula of frequency margin,the resonance margin of the normal impeller and the abnormal impeller is far greater than the safe range,so the resonance risk will not occur.