High Advance Ratio Effects on the Aerodynamics and Blade Dynamics of a Slowed Helicopter Rotor

医疗急救服务面临着在不到一小时的关键响应时间内到达偏远地区的挑战。带有额外螺旋桨的创新“复合”直升机，如空中客车直升机的原型X³，旨在通过高巡航速度和垂直起飞能力的结合来应对这一挑战。为了避免高巡航速度对推进桨叶的影响，复合直升机的主旋翼以降低的转速运行。旋翼后倾叶片上相应的反向流动对直升机的性能和稳定性有不利影响。该项目侧重于对反向流场的详细研究，以提高我们对复合直升机空气动力学的了解，并最终设计出更快的直升机，减少对紧急情况的响应时间。实验证明了回流对转子功率和载荷的影响。为了有效地抵消这些负面影响，本项目将研究反向流场本身及其对转子叶片变形的后续影响。反流场的特点是高推进比，即飞行速度与叶尖速度的关系。通过控制推进比，可以测量其对慢速转子反流场和叶片变形的影响。这些测量反过来将改进复合直升机构型概念设计中使用的气动旋翼代码，这些代码目前不足以准确预测反向流场中的复杂流动物理。拟议的项目将与马里兰大学的阿尔弗雷德·格索旋翼飞机中心和琼斯空气动力学实验室合作进行。在格伦·l·马丁风洞中，一个四叶减速模型转子将以高推进比进行测试。采用时间分辨立体粒子图像测速法和立体摄影测量法，同时测量后退叶片的反流场和变形。在这个项目中，最先进的设备、资金充足的风洞试验和研究人员的专业知识的结合对于研究慢速旋翼上的反向流动和改进未来复合直升机的设计至关重要。

Medical emergency services face the challenge to reach remote locations within a critical response time of less than an hour. Innovative "compound" helicopters with additional propellers, such as Airbus Helicopters' prototype X³, are designed to meet this challenge through a combination of high cruise velocities and vertical take-off capability. To circumvent the impact of high cruise velocities on the advancing blade, the main rotor of a compound helicopter operates at a reduced rotational speed. The corresponding reverse flow on the retreating blade has detrimental effects on the performance and stability of the helicopter. This project focuses on the detailed investigation of the reverse flow field to advance our knowledge of compound helicopter aerodynamics and ultimately design faster helicopters that reduce response times for emergency situations.Experimental evidence shows the impact of reverse flow on the rotor power and loads. To effectively counteract these negative effects, this project will investigate the reverse flow field itself and its subsequent effects on rotor blade deformations. The reverse flow field is characterized by a high advance ratio, the relation of flight speed to blade tip velocity. By manipulating the advance ratio, we can measure its effects on the reverse flow field and blade deformations of a slowed rotor. These measurements, in turn, will improve the aerodynamic rotor codes used in the conceptual design of compound helicopter configurations, which are currently insufficient for accurate prediction of the complex flow physics in the reverse flow field. The proposed project will be carried out in cooperation with the Alfred Gessow Rotorcraft Center and Jones Aerodynamics Laboratory at the University of Maryland. A four-bladed, slowed model rotor will be tested at high advance ratio in the Glenn L. Martin Wind Tunnel. The reverse flow field and deformations of the retreating blade will be measured simultaneously by time-resolved stereo particle image velocimetry and stereo photogrammetry, respectively. The combination of state-of-the-art facilities, a fully funded wind tunnel test, and researcher expertise in this project is essential to investigate reverse flow on a slowed rotor and improve the design of future compound helicopters.