An aerodynamic analysis of a ducted fan for vertical take-off and landing unmanned aerial vehicles was performed using computational simulation. A commercial computational fluid dynamics tool was used to solve the Reynolds-averaged Navier-Stokes equations. The calculated results were validated in the subsonic wind tunnel at Hanyang University. The objective of this study is to investigate the aerodynamic performance of a ducted fan in crosswinds. The thrust, normal and side forces of the ducted fan are affected by the velocity magnitude and in-flow angle of the crosswind. The pitching moment of the ducted fan is significantly influenced by the crosswind due to asymmetric lift force created by the difference in suction velocity magnitude on the duct lip. Flow separation at the duct lip occurs under hovering and crosswind conditions. The inlet flow fields of the ducted fan are distorted by the duct lip separation. In conclusion, to improve the stability of the ducted fan, the pitching moment must be reduced.

Ducted fans have higher thrust performance, higher propulsion efficiency and lower noise characteristics due to their duct system compared with commercial isolated propellers. The purpose of this study is to present design procedures in order to improve the aerodynamic performance of the ducted fan for the small VTOL UAV propulsion. In addition, the duct effect of ducted fans is analyzed to satisfy design requirements and improve performance. Aerodynamic design of the rotor and the stator blades of the ducted fan involves a series of steps: meanline analysis, through-flow analysis and aerodynamic analysis, based on consideration of the design requirements. The thrust performance of the ducted fan is somewhat higher compared with that of the rotor only, but wind tunnel test results of the ducted fan do not satisfy the design requirements. The thrust performance of the ducted fan is significantly different in the CFD results and wind tunnel results due to the inconsistency of the intake and the duct shape. Therefore, the thrust performance of the ducted fan would be somewhat improved by the optimization of the intake and the duct shape.

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.

The aerodynamic characteristics of a ski jumper model in various postures are analyzed using a commercial computational fluid dynamics tool. The purpose of this study is to understand the aerodynamic characteristics of ski jumping. The range of flying postures for ski jumpers is determined as widely as possible to simulate the optimal flight position of ski jumpers. The computational results are in good agreement with experimental results. The aerodynamic characteristics are influenced by the hip and body angles of the ski jumper model during the flight. The lift-to-drag ratio of ski jumpers is increased as hip angle increases. However, as the hip angle increases, the region of the angle of attack becomes restricted for stable flight. The augmentation of the body angle can enhance the most favorable angle of attack, because the body angle is likely to result in a cambered airfoil. In conclusion, the ski jumper should maintain a high hip angle with an angle of attack that stabilizes the flight condition, to improve flight distance.

In this study, aeroacoustic characteristics of combined fan are investigated and noise was reduced by applying Serrated Trailing Edge which is known as the method to reduce fan noises. Unsteady CFD (Computational Fluid Dynamics) analysis was carried out using Lattice Boltzmann Method(LBM) to figure out the combined fan's aeroacoustics and experimental results was used to verify simulation results. Results show that different BPFs are generated at the each inner fan and outer fan on the different frequency while Blade Passing Frequency(BPF) of general fans is constant on the entire frequency range. Boundary vortex and vortex shedding are suppressed or dispersed by applying the Serrated Trailing Edge to the inner fan. Furthermore, broadband noise and fan's torque are reduced.