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

直升机在地面效应下的绕流拓扑与地面效应外的绕流拓扑有很大的不同。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，在松软的地面上飞行时，沙子或雪可能会上升，最终阻碍飞行员的视线。这些影响对地面人员和直升机机组人员构成严重的安全问题，拟议的项目将从数值和实验两方面密切研究地面对直升机的影响。在IAG，现有的模型直升机将获得新的测量设备，用于测量桨叶变形，随后将进行地面效应内外的飞行实验。在数值方面，将增强强流固耦合，以模拟接近地面的机动飞行，例如在启动或着陆期间发生的情况。为了从实验中代表正确的飞行路径，驾驶模型必须再现适当的控制输入。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。作为项目中最后一次也是最大的实验，德国航天中心哥廷根中心将使用那里可用的真实的直升机收集自由飞行数据。调查的重点在于尾流行为，使用德国航天中心开发的BOS方法进行测量。此外，研究直升机还配备了其他传感器，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表明，一段时间后，尖端涡流不再可检测。据推测，涡配对或其他耗散现象显着降低涡强度。然而，确切的原因尚不清楚，应在项目中通过上述实验和伴随的数值模拟来探索。验证后，计划进行额外的数值参数研究，集中于地面效应中流动拓扑的各种影响因素。在仿真中，直升机的飞行路径或几何特性可以很容易地改变，而不需要新的飞行。此外，不同飞机部件上的载荷和力矩可以预测，而不需要全尺寸的研究直升机来生成飞行数据。

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.