旋翼模型垂直下降状态气动特性风洞试验

Wind tunnel test on aerodynamic characteristics of rotor model in vertical descent

摘要:

直升机垂直下降状态中包含极为危险的涡环状态.为提高对涡环状态的认识以及掌握其气动载荷、流场变化,并为相应数值模拟及飞行仿真提供试验数据,采用直升机垂直升降试验台以及大视场PIV试验测量系统在Φ5 m立式风洞对Bo-105旋翼模型进行了垂直下降状态的气动载荷以及流场测量.在桨尖马赫数相似的情况下,得到了该旋翼模型在不同总距、不同下降速度情况下的平均拉力和功率变化,以及较大范围的详细流场图像,分析了旋翼模型气动载荷变化现象,并进一步揭示了旋翼模型垂直下降状态下流场的演化发展过程.试验研究表明:旋翼模型垂直下降速度达到8 m/s后,拉力和功率急剧下降,且其各自均方根误差值显著增大；旋翼模型总距越小,对应的旋翼拉力值随垂直下降速度增大而迅速减小,越易进入“涡环状态”；桨尖涡结构不稳定的主要内因是形成了“涡对”结构,相邻桨尖涡之间的距离越近,桨尖涡越不稳定；桨尖涡聚集形成“涡环”以及涡环结构的动态演化是旋翼性能突变的关键因素.

Abstract:

Helicopter vertical descend state contains extremely dangerous vortex ring state. In order to improve the understanding of the vortex ring state, to master its aerodynamic load and flow field changes, and to provide experimental data for the corresponding numerical simulation and flight simulation, the aerodynamic load and flow field measurement test of Bo-105 rotor model under vertical descend state was conducted in Φ5 m vertical wind tunnel using helicopter vertical flight test rig and the large filed PIV measurement system. In the case of similar tip Mach number, the average thrust, average power, and wide range PIV flow field images of this rotor model under different collective pitch and descent speeds were obtained, the rotor model aerodynamic load variation was analyzed, and the flow field development process under different descent speeds was captured. The test research shows that the thrust and power decreased sharply after the vertical velocity of the rotor model dropped to 8 m/s, and the root-mean square error increased significantly. The smaller the collective pitch, the easier it was to enter vortex ring state, and the faster for the rotor model thrust to decrease with the increase of vertical descent speed. The main cause of instability of blade tip vortex structure is the vortex-pair structure. When the distance between adjacent blade tip vortices was smaller, the blade tip vortex was more unstable. The formation of vortex ring by the blade tip vortices gathering together and the dynamic evolution of the vortex ring structure were the key factors in the sudden change of rotor performance.