Numerical Investigation On Rotating Stall In Power Plant Centrifugal Fan

G4-73 centrifugal fans are widely used in 300MW thermal power units, as the result of the load changes, fouling or installation reasons, the centrifugal fans often run at the low flow rate, in such condition, the rotating stall occurs frequently, even the surge and other instable flow may occur if in the traffic condition, it will directly threat the safe operation of the units. To improve centrifugal fan operating efficiency, extent steady operation range, it is of great significance to investigate and master the rotating stall instable flow mechanism in centrifugal fan.In this paper, first of all, the 2D non-compressible Reynolds-Averaged Navier-Stokes equations were built to simulate the flow around the airfoil of G4-73No.8D centrifugal fan, a detailed numerical simulation under different angle has been carried out based on the Realizable k ?εturbulence model with software Fluent. The characteristics of airfoil stall were studied at low Reynolds number, the relationship between incidence angle and the separation point have been discussed. It concludes that, with the increase of the attack angle, the separation point gradually moves to the leading edge of the airfoil, until it enters into the stall, the suction side of the airfoil where locates the wall appears a strong vortex while in the stall.The paper based on the User-Defined Function (UDF) -it is a user interface that the Fluent software provides to program, the supposed throttle model which locates outlet of the fan is obtained. According to continuously adjust the throttle opening to achieve the numerical simulation of the rotating stall in small flow rate of the G4-73 centrifugal fan. The flow of design condition and stall condition were compared, the instantaneous velocity field and instantaneous pressure field were analyzed under the different stages of stall. The results show that, with the decreasing of the throttle opening, the fan gradually enter the stall area, there appears a significant low-speed area in the impeller, there appears back flow near the front cover, with the advance of the time step, back flow gradually spread to the rear cover, until it fills the entire channel.