Experimental and numerical investigations on the implications of aerodynamic ground effect in manoeuvring flight

直升机在地面效应下的流动拓扑与非地面效应直升机周围的流动拓扑有很大的不同。旋翼载荷、机体的振动水平以及直升机的性能都有很大的偏差。此外，当飞越松散地面时，沙子或雪可能会上升，最终遮挡飞行员的视线。这些影响对地面人员和直升机机组人员构成了严重的安全问题。拟议的项目将从数值和实验两个方面密切调查地面对直升机的影响。在IAG，现有的模型直升机将接收新的叶片变形测量设备，随后将进行地面效应内和外飞行试验。在数值方面，强流固耦合将得到加强，以便能够模拟接近地面的操纵飞行，例如在启动或着陆时发生的情况。为了从实验中表示正确的飞行路线，飞行员模型必须重现适当的控制输入。这一新的代码功能将使用之前获得的飞行数据进行测试和验证。作为该项目中最后也是最伟大的实验，将使用那里提供的真实直升机收集Göttingen自由飞行数据。调查的重点是尾流行为，用德国洛桑联邦航空航天中心发展的BOS方法测量。此外，研究直升机还配备了更多的传感器，例如控制输入、转速和桅杆力矩。这些数据将用于验证IAG在项目期间开发和建立的工具链。到目前为止的所有实验研究都表明，经过一段时间后，尖端涡流不再被检测到。假设涡对或其他耗散现象会使涡旋强度显著降低。然而，确切的原因尚不清楚，将在项目中通过上述实验和伴随的数值模拟来探索。在验证后，计划进行更多的数值参数研究，重点是各种因素对地面效应中流动拓扑的影响。在模拟中，直升机的飞行路线或几何属性可以很容易地改变，而不需要新的飞行。此外，不需要使用全尺寸的研究直升机来生成飞行数据，就可以预测飞机不同部件上的载荷和力矩。

The flow topology around helicopters in ground effect is substantially different from the one out of ground effect. Rotor loads, vibration levels of the airframe as well as the helicopter performance deviate significantly. In addition, when flying over loose ground sand or snow may rise, obstructing the pilot's view eventually. Those effects constitute a serious security problem for ground personnel as well as the helicopter's crew.The proposed project will closely investigate the ground effects on the helicopter numerically as well as experimentally. At IAG, the existing model helicopter will receive new measurement equipement for blade deformations and subsequently flight experiments in and out of ground effect will be undertaken. On the numerical side, the strong fluid-structure coupling will be enhanced to enable the simulation of manoeuvring flight close to ground, as happens for example during start or landing. In order to represent the correct flight path from experiments, a piloting model has to reproduce appropriate control inputs. This new code functionality will be tested and validated using the flight data gained previously.As last and greatest experiment within the project, at DLR Göttingen free-flight data will be gathered using a real helicopter available there. The focus of the investigations lies on the wake behaviour, measured using the BOS method developed at DLR. In addition, the research helicopter is equpped with further sensors, for example for control inputs, rotational speed and mast moments. Those data will be used for validation of the toolchain developed and established at IAG during the project.All experimental studies up to now show that tip vortices are no more detectable after some time. It is supposed that vortex pairing or other dissipative phenomena reduce the vortex strength significantly. However, the exact reasons are yet unknown and shall be explored in the project by said experiments and accompanying numerical simulations.After validation, additional numerical parameter studies are planned, concentrating on various influence factors on the flow topology in ground effect. In simulations the flight path or geometrical properties of the helicopter can be changed easily without new flights necessary. Furthermore, loads and moments on different aircraft parts are to be predicted without needing a full-scale research helicopter for flight data generation.