涵道风扇空气动力学特性分析

Aerodynamical Characteristics Analysis of Ducted Fan

涵道风扇较同样直径的孤立风扇能产生更大的升力,且风扇环括在涵道内,既可阻挡风扇气动声向外传播,又结构紧凑、安全性高。以此为升力面和飞行操纵面可构造出多种小型垂直起降无人飞行器。该类无人飞行器在前飞时,涵道处于前方来流和风扇吸流的复杂气流中,其升力、阻力和俯仰力矩对整机的配平乃至稳定控制具有决定性影响。本文对涵道风扇风洞吹风测力试验结果进行了分析研究,并进而提出:前飞时涵道阻力较大,涵道风扇若作为升力装置仅适用于强调悬停和低速飞行性能的飞行器;此外,涵道风扇式飞行器在大速度前飞时,为了实现纵向配平,整机重心垂向位置需要高于涵道阻力作用中心。

Compared with the propeller or the rotor, the ducted fan provides a larger aerodynamic thrust （lift） and the low noise due to the shrouding duct. It can be used in small VTOL UAVs because of its compact structure and the high safty. In forward flight for the kind of VTOL UAV, the ducted fan can work on the complicated flow field. The major problem is the longitudinal trim problem caused by the momentum drag and the pitch moment created by the duct. According to test data of the ducted fan, the duct lift, the momentum drag and the pitch moment are analyzed. Results show that the ducted fan is only suitable for aircrafts operated under hovering and low speed flying condition. If the ducted fan is used as a lift device for the longitudinal trim of the ducted fan aircraft in forward flight, the center of gravity of the aircraft is higher than that of the resultant drag of the ducted fan.