Performance Of A Variable-pitch Axial Fan Under The Asynchronous Regulation Of Two Stage Rotors

Considering the advantage of large capacity and superior performance in variable-operating conditions, a two-stage variable-pitch axial fan has been widely used in the air and gas system of large-scale coal-fired power units as primary fans. In practical operation, asynchronous regulation of blades is occasionally occurred, which is one of the major risks affecting the performance and stability during the running of axial flow fans.Taking a two-stage variable-pitch axial fan used in a 600 MW power unit as an example, the numerical simulation is carried out using Fluent. Firstly, the aerodynamic performance of the fan, the work capability of impellers and noise characteristics are investigated under the abnormal installation angle deviation on two blades which located at the same circumferential position, and a comparison with the situation of single abnormal blade located at the first-stage or the second-stage impeller is conducted. Then, taking circumferential position relationships of abnormal blades which located separately in two impellers as examples, the variations of fan performance and internal flow characteristics in different abnormal situations are examined.Results show that, when the installation angle on two blades deviates from normal values simultaneously, the work capability of impellers, the efficiency of two guide vane stages, noise and operating performance of the fan are all inferior to the case of single abnormal blade; the stall region is expanded, especially for the case of positive deviation of blades. With the increase of Δβ, the situation of negative deviation has a higher impeller acting ability, and the noise level of the fan tends to increase generally, while the positive deviation has a greater impact on the acoustic source power distribution of the abnormal impeller than the negative deviation. Under the case of positive deviation, flow losses of guide vane are larger than those in negative deviation. Different circumferential position relationship of abnormal blades has different impacts on fan performance and flow characteristics. Using the description in this paper, the situation when the positive deviation of FAB(the first abnormal blade) and 3# leads to the most violent varations of the fan’s performance and flow characteristics, while the situation when the deviation of FAB and 4# has a little slighter effect on the fan compared with the former situation. The other two situations affect the fan in a much less extent than the two former cases, furthermore, the fan performance and flow characteristics vary least while FAB and 2# deviate simultaneously.