Effect of a casing fence on the tip-leakage flow of an axial flow fan

The effect of a casing fence on the tip-leakage flow of an axial flow fan is investigated using large eddy simulation. A fence is attached on the shroud near the trailing edge of an axial flow fan used in an outdoor unit of air conditioner. The Reynolds number is 547,000 based on the blade tip radius and tip velocity. At the design condition, the fan efficiency is increased by the casing fence. The roles of the fence are to block backward leakage flows near the shroud and to weaken the movement of the tip-leakage vortex (TLV) in the azimuthal direction. Also, the fence reduces the double-leakage tip-clearance flow generated at the aft part of the blade tip due to the TLV-blade interaction, reducing the strength of the tip-separation vortex. Consequently, the tip leakage and total pressure losses are reduced, and the efficiency is increased. The pressure fluctuations on the aft part of the blade tip of the pressure surface caused by the TLV-blade interaction are also significantly reduced by the fence, indicating reduction of the noise source. According to the interaction between the fence and backward leakage flow induced by the TLV, the fence significantly and slightly increases the aerodynamic performances at the design and peak efficiency conditions, respectively, but reduces them at an overflow condition.