主旋翼尾流对尾桨涡环状态的影响机制研究

Tail rotor vortex ring state (VRS) is a dangerous case of helicopter when flight in the crosswind and sideslip or turning around. It causes loss of tail rotor effectiveness (LTE) so that the fuselage would encounter unanticipated yaw and may be crash. Research has shown that the main rotor wake in some case can postpone the tail rotor VRS, so reasonable utilization of the main rotor/tail rotor aerodynamics interference in the aerodynamic configuration design of tail rotor can enhance the counteracting capability of tail rotor against Side Wind. However, the main rotor wake spatial evolution characteristics of helicopters with different take-off weight in the crosswind condition and the influence mechanism of main rotor wake on the VRS of tail rotor are not fully understood. This project aims to research and reveal the following problems by combining the CFD and wind tunnel test method: 1. To elucidate the wake spatial distribution characteristics of different disc loading main rotor in the crosswind environment. 2.Clarify the changes of tail rotor blade tip vortices convection behavior and tail rotor profile characteristics distribution under the main rotor wake interference, and then reveal the influence mechanism of the main rotor wake on the VRS of tail rotor. 3. Reveal the influence mechanism of the tail rotor layout parameters on its VRS, inductive layout design guidelines of tail rotor for helicopter with different take-off weight. Research results will provide scientific basis and guidelines for the design of tail rotors which counteracting crosswind for helicopters with different take-off weight, and can provide a theoretical basis for the determination of tail rotor VRS boundary criterion and wind-limitation envelope for helicopter with different aerodynamic configurations.

尾桨涡环状态是直升机在侧风环境飞行以及侧滑、转弯机动时发生的一种危险状况，可能导致偏航失控甚至引发坠机事故。目前已知旋翼尾流在某些情况能推迟尾桨进入涡环状态，在尾桨气动布局设计时合理利用旋翼尾流干扰有助增强尾桨的抗侧风性能，但尚未能完全阐明不同起飞重量直升机在侧风下旋翼尾流的空间演化特征及其对尾桨涡环状态的具体影响机制。本项目将结合数值模拟和风洞试验研究并揭示以下问题：1.揭示侧风环境下不同桨盘载荷主旋翼尾流的空间演化特征；2.阐明旋翼尾流干扰下尾桨桨尖涡运动行为和尾桨剖面气动特性分布的变化特征，揭示旋翼尾流对尾桨涡环状态边界和气动性能的影响机制；3.揭示尾桨气动布局参数对其涡环状态的影响机理，归纳不同起飞重量直升机的抗侧风尾桨布局设计准则。通过本项目研究，可为不同起飞重量的直升机抗侧风尾桨气动布局设计提供科学基础，并为不同气动布局直升机尾桨涡环状态边界判据和风限图的制定提供理论依据。

尾桨涡环状态是直升机在侧风环境飞行以及侧滑、转弯机动时发生的一种危险状况，可能导致偏航失控甚至引发坠机事故。旋翼尾流在对尾桨性能具有重要干扰作用，研究旋翼尾流对尾桨涡环状态的影响机制有助于增强直升机在复杂环境下的飞行安全性。本项目开展了侧风环境下主旋翼尾流的演化特征、旋翼尾流对尾桨涡环状态干扰机制、揭示尾桨气动布局参数对涡环状态的影响研究。研究结果表明：随着风速增加，旋翼尾流结构逐渐由柱状滑流向扁平状尾流演化，由旋翼上下表面压差导致的桨盘涡对尾桨气动特性具有重要干扰作用。尾桨桨尖涡聚集导致的诱导速度增加是引起涡环状态下气动性能下降的主要因素，涡环结构的动态变化导致了尾桨气动性能波动增加。在旋翼桨盘涡干扰的影响下，该桨盘涡旋转方向与底朝前尾桨的转向相反，增强了尾桨的前缘动压；此外，尾桨桨尖涡聚集的涡环结构向旋翼内侧移动，减小了桨尖涡聚集对尾桨性能的影响，从而减弱了尾桨的涡环状态效应。底朝前转向尾桨能产生前缘动压增强效应，因而气动性能优于底朝后转向尾桨。高位布局尾桨较接近于旋翼桨盘涡，涡环状态下的拉力优于底位布局尾桨。该结论对尾桨布局设计具有指导意义。耦合了主旋翼尾流模型与涡环状态入流模型，建立了涡环状态下尾桨气动性能快速评估方法。该模型能够为气动布局初步设计、飞行力学仿真、飞行控制仿真提供尾桨性能快速评估。