Influence of tip clearance and propeller separation space onaerodynamic performance of ducted propeller

The aerodynamics of flow field around the ducted propeller system in hover was simulated to investigate the influence of tip clearance and propeller separation space on aerodynamic performance individually around the unsteady Euler equations with unstructured sliding mesh technique. The tip clearance ratio varied between 0 and 1.37%, and the propeller separation space range was 0.25-0.65 times of propeller radius. The investigation shows that increasing tip clearance leads to decrease in total trust and power loading of ducted propeller. The critical tip clearance ratio is about 1.10%. The magnitude of leakage vortices increases dramatically at the critical tip clearance, causing significant change of the thrust sharing ratio between duct and propeller; the proportion of duct thrust to total trust decreases by 10.27%, and system aerodynamic performance worsens rapidly. The unsteady characteristic of tip clearance flow appears at large tip clearance ratio. Increasing propeller separation space can improve aerodynamic efficiency of ducted coaxial propeller. However, the influence is denotable as the relative variation in aerodynamic force is within 3%, due to the diffusion effect of duct on propeller slipstream.