计入畸变修正的旋翼尾迹前飞状态稳定性分析

现有的旋翼尾迹稳定性分析方法在涡线过近处会得出不现实的过大发散率结果,因而存在一定的局限性。为了消除这种前飞状态下尾迹高度畸变对其稳定性分析所造成的不合理干扰,提出了一个旋翼尾迹在正弦扰动下,结合涡线畸变修正的线性化稳定性分析方法。在该方法中,将尾迹涡线离散为一系列涡元,并对其端点施加沿尾迹涡线分布的正弦扰动;考虑了桨尖涡的自诱导、互诱导以及与桨叶的干扰作用,并创新地引入在伪涡核对稳定性分析中,因尾迹高度畸变产生的不合理干扰而进行的修正。以H-34型直升机旋翼模型为例,在前飞状态下,重点计算分析了尾迹向后飘移、涡核大小和前飞速度等对旋翼尾迹稳定性的影响。研究结果表明:引入伪涡核模型可以有效地修正在涡线过近处所产生的不现实稳定性分析结果;前飞速度、涡核大小等因素会在一定条件下有限地影响尾迹的不稳定性,但都不改变前飞状态旋翼尾迹的本质不稳定性。

Analysis of Rotor Wake Stability in Forward Flight Associated with Distortion Revise

The state of the art in the analysis of rotor wake stability has its limitation that it will obtain impractically large divergence rate where the vortex filaments get too close. In order to eliminate this unreasonable interference in the analysis of rotor wake stability coming from highly distorted wakes in forward flight, a linearized method of wake stability analysis associated with wake distortion revision under a sinusoidal perturbation is presented. In this method, the wake vortex filaments are discretized into a series of vortex elements with a sinusoidal perturbation distributed on the nodes along the vortex filaments, where the self/mutually-induced velocity of wakes and the influence of blades is considered. A fake vortex core is novelly applied to revise this unreasonable interference in the analysis of rotor wake stability coming from highly distorted wakes. Taking the H-34 model rotor as a numerical example, the influence of wake drifting, size of vortex core and advance speed on rotor wake stability are calculated by this method and analyzed individually in forward flight. The results show that the fake vortex core can effectively revise the impractically large divergence rate where the vortex filaments are getting too close. Furthermore, in forward flight, the change of the size of vortex core or advance speed, etc., cannot change the inherent instability of rotor wakes, but it can slightly influence the instabilities under some conditions.