直升机涡环状态速度边界的试验研究

An Experimental Investigation on the Boundary of Helicopter Vortex-Ring State

直升机作带功率下降时，若操纵不慎，容易陷入涡环状态，如果没有足够的高度，就会造成坠地事故。目前，与涡环现象有关的飞行事故仍时有发生。因此，中国民航与南航直升机所合作开展了‘直升机如何避免涡环事故’的课题研究。模型试验研究是在南航直升机研究所自行研制的大型试验设备──旋臂机上进行的。本文介绍了继垂直升降试验之后的斜下降试验，试验结果显示出涡环状态中旋翼气动力和力矩的非定常特性以及不同下滑角的影响，尤其是发现了旋翼进入涡环状态的特征现象──旋翼扭矩的反常变化。据此，得出进入涡环状态的速度边界。

The helicopter behavior in vertical or steeply oblique descent has been of great concern in rotorcraft engineering because there is an unsteady and unsafe region known as the 'vortex-ring state' condition can apply to both main and tail rotors. Although a number of investigations have been published on the subject,there are still many questions to be answered. Especially,the existing theories fail to give a satisfactory method for predicting the boundary of the vortex-ring state. For this purpose, a series of model tests on vertical and oblique descents have been conducted on a newly-built test apparatus-the Whirlign Beam. The variations of the rotor torque, thrust, and pitch and roll moments with flight speed were obtained,which show some unsteady aerodynamic behavior of the model rotors working in the vortex-ring state. The results also show that the various flight path angles have a strong impact on these phenomena. A very irregular variation of the mean torque at low rate-of-descent was observed here for the first time. We consider this to be the start of the 'power setteling'. The critical flight speeds corresponding to the start of the 'power setteling' in oblique descents with various path angles are plotted on a Vx-Vy plot,so that a boundary of the vortes-ring state is obtained experimentally.