Modified Lifting Line Method Based on Vortex Rings and Its Application on Lift Fan Design

The image vortex model is widely used in lifting line method to predict the fl ow induced by the shroud and hub surface in ducted fan, but it does not perform well in lift fan design due to the zero far fi eld in fl ow. In this paper the theoretical defects and numerical error propagation characteristic of the image vortex model in simulating duct surface are studied. Then the vortex rings correction based on image vortex model is veri fi ed and applied in lifting line method. In order to test the improved method, a 150 mm diameter lift fan is designed by the modi fi ed lifting line method, after that, analyzed by the modi fi ed lifting line itself and RANS solver respectively. The results show that the contribution of the vortex rings at the rotor accounts for 50% of the total induced velocity, and it accounts for 35% at the stator, which veri fi es the necessity of the vortex rings correction. The performance of the rotor and stator geometry is consistent with the design expectation, the e ffi ciency is up to 90.97% by numerical simulation and 88.32% by experimental measurement, which con fi rms the reli-ability of the modi fi ed lifting line method developed in this paper especially on lift fan design.