Study On The Dynamic Mechanism Of Rotating Stall In Axial-flow Fans For Power Plants

Axial fan with adjustable vanes has been widely used. The flow rate of axial fan is large and the structure is compact. Axial fan with adjustable vanes has good economy in time-varying conditions. As the parameters of fan improving, the work environment is severe and the blades of impeller are often damaged. One of the important reasons is that the fan runs in the stall e zone in a long time. Therefore, it has a significant theoretical meaning and engineering value on safe operation of the axial fan in power plants to research the strength of the fan on stall conditions.In this paper, an axial fan with adjustable vanes of a certain power plant is taken as the research subject. The rotating stall phenomenon was simulated by using the numerical software Fluent. Five typical conditions are presented and discussed, involving the design condition, near stall condition, conditions on occurrence and development of stall inception, the rotating stall condition. The results show that the flow field inside the impeller changes significantly after the stall occurs. A strip of high entropy generation areas is discovered near the top of the blades on stall inception condition. During the development of stall cells, the high entropy generation areas become larger. Three high entropy generation areas are discovered. On the stall condition, the three high entropy generation areas merge into one and the fan come into a relative steady condition.Based on the flow characteristics of the impeller under the stall conditions, the fluid-solid coupling characteristics of the impeller were obtained using the software ANSYS. The results show that the equivalent stress distribution of the impeller has little change compared with the design condition. The total deformation of the impeller is non-uiform and the aerodynamic force has great impact on the total deformation. The max total deformation appears at the location of the center of the stall cell. The max total deformation is 133.3% larger than the design condition. The modal analysis of the impeller under different loads has been studied. The centrifugal force has an important influence on the natural frequency and vibration mode. The aerodynamic force has little effect. When the rotate speed is between 1400r/min and 1535r/min, this is the avoid rate is between-6% and 3%, there is a resonance point k=m=10 for the impeller. The resonance rotate speed is 1481r/min and the resonance margin is 0.61%. The resonance margin is so small that the k=m=10 resonance may easily occur in impeller.