Research On The Effect Mechanism Of Abnormal Blade Angle On Stall Inception In A Two-stage Variable Pitch Axial-flow Fan

By changing the installation angle of the rotor, the adjustable axial fans adjust the flow to keep the high efficiency in a large flow range during the operation. It is an efficient adjustment way to reduce the loss of throttle effectively. At present, there is a phenomenon occurs, which one or more moving blade installation angles will float or not synchronized with the other moving leaves during the running of the adjustable axial fans. The phenomenon will cause the change of the fan characteristic curve, even more, the blanketing phenomenon will generate when a slight disturbance appear in the axial fans. The operating performance and efficiency is affected seriously by the phenomenon.In this paper, the two-stage adjustable axial fans of a power plant is studied, the single abnormal blade appear in the first and second rotor, respectively. The starting position and style of the stall inception, so as the 3D unsteady evolution process of the rotating stall are analyzed. The analysis results show that: firstly, the existence of the single abnormal blade, both in the first and second rotor, will cause the axial fan fall into rotating stall in advance. That is to say, it makes the stable operation range of the axial fan decreases. When the single abnormal blade is in the second rotor, the influence of the positive abnormal angle is greater than the influence of the negative abnormal angle. Meanwhile, when the abnormal blade is in the first rotor, the influence of the big abnormal angle is greater than that the little abnormal angle. Secondly, the single abnormal blade, existed in the first and second rotor, has no effect on the initial position of the rotating stall, the rotating stall coming into being in the second rotor firstly. And the mechanism of stall induced is same to the situation that there is no abnormal blade, the type of stall inception is spike. Finally, the existence of abnormal blade has influence on the rotating stall evolution process. Namely, the rotational speed of the stall inception and stall cell is different between the first and second rotor, respectively. During the evolution process from stall inception to stall cell, there three dimensional unsteady evolution characteristics exist significant differences.