The Effect of Tip Clearance on Performance of a Counter-Rotating Ducted Fan in a VTOL UAV

Abstract

This research analyzed the effect of tip clearance on counter-rotating ducted fans for vertical take-off and landing in unmanned aerial vehicles using commercial computational fluid dynamics tools. The computational results were verified using the subsonic wind tunnel at Hanyang University. In this study, the tip leakage flow of the counter-rotating ducted fan was analyzed in order to enhance the fan performance. The thrust coefficient decreases with increasingly larger front rotor tip clearance due to the increase in tip leakage flow. The power coefficient is influenced by viscous and tip leakage losses from the large tip clearances for the rear rotor. Smaller figures of merit are captured at larger tip clearances for the front and rear rotors because the direction of vortex core changes quickly. In conclusion, to improve the aerodynamic performance of counter-rotating ducted fans, it is necessary to reduce the mass flow rate across the tip clearance and tip vortex loss.