Dynamic Characteristics Analysis Of Axial Fan Impeller In Power Plant Based On Fluid-structure Interaction

The fan is widely used in many fields of national economy. With the increase ofcapacity of power generating sets, variable pitch axial fans are always adopted in largepower generating sets. The impeller is a key component of the fan, and the insufficientstrength of the impeller will induce a fatigue failure in the fan operation. In the traditionalstrength calculation of the fan, the impeller structure is simplified a lot and it will causebig error. The finite element analysis method is able to make up for the shortage andaccurately forecast the impeller security.Based on FSI analysis method, the static structure analysis of a variable pitch fanimpeller is carried out through numerical simulation. The calculation results show thatthe aerodynamic force has great effect on the static characteristic of the impeller.Considering the fluid-structure interaction, the equivalent stress distribution of the bladestends to be more uneven and the maximum equivalent decreases. The total deformationdistribution of the blades changes a lot. In addition, the safety of the impeller operation isestimated. The allowable stress of the impeller material is90MPa and the maximumequivalent stress of the impeller is much less than this value, so the static strength of theaxial fan meet the requirements.The dynamic characteristic of the impeller is analyzed in this paper. The modalanalyses of the blade and wheel disc are carried out firstly, and the natural frequencies ofthe blade increase to a certain extent after loading the pre-stress. Among the differentstress, the centrifugal force has a biggest effect on the model frequency and thefrequencies increase with the increase of rotate speed. The natural frequencies of theimpeller on different harmonic index are obtained by the impeller model calculation.Different order model of the impeller are analyzed in detail when harmonic index is1.The frequency margin between the fifth and sixth order model frequency with thefundamental frequency is about9.4%and it is less than the margin of safety inengineering. It means that the main frequency of airflow is located in the local resonanceregion of fifth and sixth order model. Because the equivalent stress of the blade tip is low,so the blade vibration will not cause the fatigue failure of the impeller.