Numerical Simulation Study On The Influence Mechanism Of Rotor Angle On Stall Inception In An Axial-flow Fan

In recent years, with the increment of power installed capacity, the variable-pitch axial fan with two-stage regulated blade have been widely applied in forced draft fans, induced fans and primary fans. However, flow phenomena such as flow separation, stall, surge and blade drift may occur. From an engineering standpoint, this research offers a valuable means to control rotating stall and ensure safe operation of the fan.In this paper, an axial fan with adjustable vanes of a certain power plant is taken as the research subject to investigate the influence mechanism of rotor angle on initial position and forms of the stall inception. The results are as follows: Under the blade installation angle of 3°, rotating stall occurs at the flow rate of 59.5 m3/s in the axial fan. The stall inception firstly appears in tip region of the second rotor, then the stall inception also appears in the first rotor. The interaction of the two stage impeller make the stall cell evolve into the mature stall cell at the same time. The stall inception shows spike type with a rotating speed of 0.75 wr, and the stall cell with a rotating speed of 0.55 wr. The simulation results of single stage axial fan shows that the rotating stall occurs at the flow rate of 55.38 m3/s in the axial fan. The stall inception shows spike type and first appears in tip region of the rotor. The three stall inception region eventually became to the three mature stall cells with the same rotational speed.The research about rotating stall on the different blade installation angle shows that the stall margin is the maximum at the blade installation angle of 3°and 9°. This is a reason why the 0°~13.5° was selected as the working range of the axial fan. The stall pressure gradually reduce with the change of the blade installation angle from the 27° to the-18°. This is consistent with the change law of pressure in surge curve. At the 27° blade installation angle, the modal wave stall inception is mainly induced by the reflux near suction surface. The stall inception first appears in tip region of the rotor and the stall inception region gradually evolve into mature stall cell. While at the other 5 blade installation angles, the spike type stall inception is mainly induced by the leakage flow near blade tip. The unsteady flow starting from the tip clearance region and the stall inception gradually evolved to the adjacent channel. A mature stall cell which occupied 50% impeller channels was formed in the impeller.