Through the explanation of the stall and surge mechanism of Qingzhou wind turbine, the stall and surge of axial fan in actual production are analyzed. The reason for the blade drift in the operation of the two-stage axial primary fan of the 600 MW unit is discussed.
Analysis of Stall Formation and Surge Formation Mechanism of Qingzhou Fans
The differential pressure before and after the axial fan blades is the same when other conditions are constant The angle of attack is determined. In the critical angle of attack, the above pressure difference is approximately proportional to the blade angle of attack, and the blade shapes of different blades have different critical angles of attack. The airfoil angle of attack does not exceed the critical value, and the airflow flows smoothly along the convex surface of the blade, but the blade angle of attack exceeds the pressure drop, and the airflow will leave the convex surface of the blade, causing boundary separation. A Ry layer is created, creating a large area of eddy currents. At this point, the total fan pressure drops, called the fan "stall".
Due to the machining error of the axial fan blades, there is an angular error in the installation of the rotor blades, and the flow direction of the impeller inlet is inconsistent. When the airflow angle of attack reaches a critical value, some blades may stall.
If the flow path in the cascade stops first, the flow will be lost. The swirl zone blocks the flow passage formed by the outflow, and the gas flowing into 3 can only turn to the flow passages 2 and 4. The split airflow reduces the angle of attack of the airflow flowing into the flow passage 2, but increases the angle of attack of the airflow flowing into the flow passage 4, causing the flow passage 4 to be blocked, so that the airflow in the vane passage gradually propagates from 3, 4, and 5. On the annular cascade of the axial fan, the number of stalls is less than one and greater than ten. When the frequency of the rotating stall, that is, the frequency of the exciting force is equal to or close to the natural vibration frequency of the blade, the blade will resonate, and the alternating stress in the resonance may reach the extent of destroying the blade.
Qingzhou fan surge is based on the characteristics of the axial fan. Fan performance curve plotted from experimental data. The axial flow fan performance curve Q-H is hump-like. The working point of the Q-H curve corresponding to the upper limit efficiency is an excellent working point, which is determined by the fan and the pipe. There is an unstable hump curve in the axial fan working area. When the fan is running into an unstable working area, the fan stalls and then the fan surges. If not handled properly, the axial fan will exit the operation and seriously damage the fan.