俯仰振荡三角翼在非定常自由流中运动的实验

Experiment on Pitching Delta Wing in Unsteady Free Stream

在南京航空航天大学已建成的国内首座非定常风洞内,研制了一套单自由度俯仰振荡实验装置,设计开发了一套对模型姿态和来流风速进行联合控制的软件。对一60°后掠三角翼模型进行了单独俯仰振荡运动和俯仰振荡与自由来流耦合运动的实验。实验结果表明:模型做单独俯仰振荡时,振动频率和振动幅值的影响只有在迟滞环出现后才起作用,而迟滞环的出现是由于翼面上的不同流态对外界扰动的反应时间不同造成的。非定常自由流对做俯仰振荡的三角翼气动特性有很大的影响,模型上仰过程中来流的减速,进一步提高了最大升力系数,推迟了失速迎角;模型下俯过程中来流的加速,则更进一步推迟了升力系数恢复到静态时的值。当翼面上产生破碎涡流时,非定常自由流的作用表现得更为明显。

A pitching test set-up, used in the unsteady wind tunnel at Nanjing University of Aeronautics ＆. Astronautics, is developed to study the effect of rapid changes on both the free stream velocity and the angle of attack. A pitching alone delta wing and the pitching delta wing coupled with unsteady free stream are tested. It is found that in the pitching alone test, the reduced frequency and the amplitude play an important role only when the hysteresis loop arises. The hysteresis loop is because the pitching motion goes through the different flow elements with different time scales. It is also found that in the dynamic pitching motion combined with unsteady free stream, the oscillating free stream velocity affects the dynamic characteristic of the pitching delta wing further. When the delta wing pitches up, the decelerating free stream makes CLmax increase and the stall angle of attack delay. When the delta wing pitches down, the recover of CL static value is delayed by the accelerating free stream. The effects of unsteady free stream are obvious when the flow field over delta wing is controlled by the breakdown vortex。