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

In recent years, due to the high efficiency and wide adjustment range, the axial fanswith adjustable vanes are widely applied in power plants. However, in actual operation,because of drastic changes in the working environment or self-regulation delay in axialfans with adjustable vanes, flow phenomena such as flow separation, stall, surge andblade drift may occur. These can lead to the decrease of total pressure and efficiency, andeven cause the equipment damage and a series of accidents.In this paper, an axial fan with adjustable vanes of a certain power plant is taken asthe research subject. By using Fluent, the steady and unsteady simulations under a certainblade installation angles were conducted. And the3D flow fields before and after rotatingstall in the1stimpeller were analyzed. The results are as follows:(1) Under the blade installation angle of3°, rotating stall occurs at the flow rate of73m3/s in the axial fan. The stall inception shows spike type with a rotating speed of0.667wr. Then it takes2or3rotation cycles for the stall inception to turn into stall cellwith a rotating speed of0.5wr. During the occurrence and development of the stall cell,along with the rotation of the impellers, the impact area of rotating stall extends along thecircumferential, axial and radial directions. Also, the flow fields and energy loss situationin the impeller change correspondingly.(2) Meanwhile, the influence of blade tip leakage flow on the stall inception isdiscussed. At near stall stage, the blade tip leakage flow gets enhanced due to thedecrease of flow, and the leakage vortex trajectory shows a trend to move to the bladeleading edge. When it comes to the critical value, the backflow rolled up by the leakagevortex blocks the blade passage, and gradually develops into stall cell. When the streamlines of the flow mixed by the leakage flow and mainstream are parallel to the frontallines of the blade leading edge, the spike stall inception first comes into being. And thebackflow at the trailing edge and the overflow at the leading edge of the next bladeindicate the formation of stall cell.