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结构与离地效应下的有很大的不同。旋翼载荷、机体振动水平以及直升机性能偏差明显。此外，当飞行在松散的地面上时，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了严重的安全问题。拟议的项目将密切调查地面对直升机的影响数值和实验。在IAG，现有的模型直升机将接受新的叶片变形测量设备，随后将进行地面和地面效应的飞行实验。在数值方面，强流固耦合将得到加强，以便模拟接近地面的机动飞行，例如在启动或着陆过程中发生的飞行。为了从实验中得到正确的飞行路径，飞行模型必须重现适当的控制输入。这个新的代码功能将使用先前获得的飞行数据进行测试和验证。作为项目中最后一个也是最伟大的实验，在DLR Göttingen自由飞行数据将使用那里可用的真正的直升机收集。研究的重点在于尾流行为，使用在DLR开发的BOS方法进行测量。此外，研究直升机还配备了更多的传感器，例如控制输入、旋转速度和桅杆力矩。这些数据将用于项目期间IAG开发和建立的工具链的验证。到目前为止，所有的实验研究都表明，在一段时间后，尖端涡不再被检测到。假设涡旋配对或其他耗散现象会显著降低涡旋强度。然而，确切的原因尚不清楚，需要在项目中通过上述实验和相应的数值模拟来探索。在验证后，计划进行更多的数值参数研究，重点研究地面效应中影响流动拓扑的各种因素。在模拟中，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，对不同飞机部件的载荷和力矩进行预测，而不需要全尺寸的研究直升机进行飞行数据生成。

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.