倾转旋翼机涡环状态数值模拟及数学建模

Numerical simulation and mathematical modeling of vortex ring state of Tiltrotor aircraft

倾转旋翼机垂直下降或斜下降过程中包含极为危险的涡环状态,为掌握涡环状态下其气动载荷、流场变化规律,建立涡环边界数学模型,为相应飞行仿真和飞行试验提供数学模型。采用基于滑移网格技术的CFD方法模拟了倾转旋翼机的涡环状态,研究了倾转旋翼机垂直下降飞行时涡环状态流场、力和力矩的演变规律,提出了倾转旋翼机涡环边界计算方法,并得出了涡环边界解析表达式。结果表明:与直升机涡环状态的主要区别为,倾转旋翼机的机翼降低了单个旋翼涡环状态的影响,但倾转旋翼机旋翼分布的对称性,提高了飞行器滚转力矩失衡的风险;倾转旋翼机垂直下降速率v_(H)/v_(h)为0.9左右时,会进入成熟的涡环状态,旋翼拉力损失最大,为18%;倾转旋翼机垂直下降时的涡环状态对应的下降速率为0.583≤v_(H)/v_(h)≤1.516,风险一方面来源于倾转旋翼机左、右两部分旋翼拉力不对称导致倾覆,一方面来源于倾转旋翼机旋翼拉力损失过大导致坠毁;根据涡环状态危险程度,建立了垂直下降和斜下降状态的涡环边界数学模型。结果可为倾转旋翼机的设计和安全飞行提供下降速度规避依据。

The vertical and oblique descend states of Tiltrotor involve extremely dangerous vortex ring state(VRS).To master the aerodynamic load and flow field changes of Tiltrotor in the VRS,the vortex ring boundary mathematical model was established,targeted for corresponding flight simulation and flight test.The CFD method based on slip grid technology was implemented to simulate the VRS of the Tiltrotor,the evolution of the flow field,force and moment of the VRS during the vertical descent flight of the Tiltrotor,with the calculation method of the VRS boundary proposed and the analytical expression of the risk zone of the VRS presented.The results show that the wing of the Tiltrotor reduces the influence of the VRS of single rotor,yet the symmetry of the Tiltrotor rotor increases the risk of unbalanced rolling moments;the Tiltrotor tends to enter the mature VRS when the descent rate v_(H)/v_(h) is 0.9,with the rotor-lift loss reaching the maximum value of 18%.Given that the descent rate corresponding to the VRS is 0.583≤v_(H)/v_(h)≤1.516 during the vertical descent state,risk may arise from the overturning caused by the unbalanced lift of the left and right rotors of the Tiltrotor,and from the crash caused by the excessive rotorlift loss of the Tiltrotor.In view of the dangerous degree of VRS,the vortex ring boundary mathematical models of vertical and oblique descent states are attempted,providing a basis for the design and safe flight of the Tiltrotor.