| 摘要 |
A fuel efficient aircraft propulsion system comprises a wingtip mounted ducted pusher fan with convergent backwash and a skewed conical engine nacelle. The system both mitigates wingtip vortex drag and converts a portion of vortex energy into propulsion force and lift force. The forward-tapering nacelle skews both downward and inward, so the lower nacelle surface is flush with the lower wing surface and the inboard nacelle surface does not alter flow over the upper wing surface. This firstly preserves lift at the outboard wing end. Secondly, air displacement by the nacelle accelerates flow only on the outboard and upper nacelle surfaces, and because the nacelle occupies the core of the nascent wingtip vortex, rotational air velocity is greatest on the upper nacelle surface. The resultant pressure drop on the upper nacelle surface contributes to aircraft lift. And because the nacelle surface tapers forward, this pressure drop does not exert backward-acting drag on the aircraft. Aft of the nacelle, the pusher fan hub surface conforms with the aft nacelle surface and tapers aft. Propulsion foils project from the forward portion of the pusher fan hub at an outward-aft angle, which directs convergent high pressure backwash flow along the aft tapering hub surface. This isolates aft-facing hub surfaces from drag-inducing vortex core pressure drop. Downstream fan backwash convergence then forms a central volume of high pressure flow where the low pressure trailing vortex core would otherwise develop. This is an efficient means to dissipate the cyclonic structure of the vortex, because vortex persistence requires low pressure core persistence. The direction of pusher fan rotation opposes the direction of wingtip vortex rotation as described in the prior art. This cross-flow interaction increases the effective power of the fan and also further counters vortex formation. An integral peripheral duct links the outer ends of the fan propulsion foils to provide thrust efficiency similar to that of a high bypass fanjet engine, but without the internal air friction within a bypass channel. In an alternative horizontal axis wind turbine embodiment, the same nacelle form supports secondary power-takeoff turbines mounted in high energy density flow at the turbine blade tips. |
