飞行器动态下俯过程中的负阻力现象

利用水洞中动态测力/流动显示一体化实验系统,研究飞行器简易模型等速俯仰过程动态气动特性.测力天平为三分量内式尾支形式;利用氢气泡方法观测机翼上表面流动,测力和流动显示结果同时记录.当下俯无量纲角速度k≥0.11时,观测到正攻角时的负阻力现象.分析测力和流动显示结果,表明负阻力是下俯过程中上翼面流动由分离向附着恢复过程中的迟滞效应引起的,负阻力的大小与下俯无量纲角速度和下俯起始攻角有直接关系.

Negative drag phenomena of aircraft in dynamic pitching process

Aerodynamic characteristics of a simplified aircraft model pitching with constant pitch rate were studied in a water tunnel. Dynamic force measurement and flow visualization were made simultaneously. The three component force measurement balance was internal type and fixed to the sting, and the flow over the wing was visualized by hydrogen bubble method. In the pitch down process with reduced pitch rate k larger than 0.11, negative drag phenomena were detected at certain positive angles of attack. Analysis of the force measurement and corresponding visualization results show that during the pitching down process, the interaction between the attaching flow of higher speed near leading edge and the stagnating fluid in the separation region causes an increase of pressure on upper surface of the wing, which causes the negative drag at a positive angle of attack. The magnitude of negative drag depends on the reduced pitch rate and the start angle of attack.