直升机飞行力学线性变参数建模方法研究

针对直升机飞行力学建模问题,分别基于模型缝合及模糊逼近提出了两种线性变参数(LPV)建模方法。在模型缝合方法中,基于经过滤波加权的飞行速度进行气动导数和操纵导数的插值,完成气动力的实时计算,结合非线性欧拉运动方程完成LPV模型的建立。在模型逼近方法中,建立了基于T-S模糊模型的非线性状态空间逼近模型,采用anfis结构完成了模糊模型训练。利用UH-60直升机非线性模型生成了不同飞行速度的线性状态空间模型,并分别通过两种方法建立了两套LPV模型。最后,基于频率响应和泰尔不等系数对典型LPV建模参数对模型精度的影响特性进行了分析。

操纵策略对高速直升机前飞性能的影响分析

针对共轴刚性旋翼高速直升机的操纵冗余问题,开展基于旋翼/推力桨气动力分配的操纵策略研究,并分析其对飞行性能的影响。首先,基于动量-叶素理论与尾迹叠加模型发展了共轴刚性旋翼和推力桨的气动模型,并采用动量源方法建立计入旋翼干扰的机身气动力CFD计算模型。其次,根据所建立的各部件气动载荷求解方法,构建高速前飞状态全机操纵与姿态配平方法。最后,分析旋翼/推力桨不同气动力分配的操纵策略对高速直升机飞行性能的影响规律。研究发现,直升机在巡航高度高速飞行时,旋翼提供部分牵引力可以有效增大高速直升机的最大前飞速度,而操纵策略改变对斜爬升率影响不大。

风-浪-舰耦合对舰船尾流场及直升机气动的影响

为研究波浪和舰船运动对高海况下舰载直升机起降的影响,建立了一套耦合风-浪-舰和直升机的多相流数值模拟方法。使用动态流体作用模拟舰船运动,采用动量源方法模拟直升机旋翼,对3~6级海况下ONRT舰船摇荡运动时的尾流场非定常气动特性进行了研究,并计算了UH-60A直升机旋翼气动载荷的时间历程。研究表明:6级海况下流场速度分量和旋翼气动载荷的波动达到5级海况的2倍,而3~5级海况之间的差别较小;悬停跟进时直升机不断出没于舰船运动导致的尾流中速度和涡量不同的区域,使得旋翼气动载荷有极强的非定常特性;在6级海况下,旋翼拉力与波浪-舰船耦合运动同周期的波动达到20%,并伴随着穿越尾流剪切层时产生的5~10 Hz的小扰动。

基于多传感器信息融合的直升机城市内障碍物主动探测方法

为了解决直升机前视告警系统在城市内告警成功率较低,对前视方向感知能力不足问题,提出一种基于多传感器信息融合的直升机城市内障碍物主动探测方法,以提高直升机前视告警的有效性。首先,研究了基于雷达与视觉信息融合的检测及跟踪方法,得到障碍物自身尺寸及经纬度数据信息。其次,提出一种障碍物数据处理方法,筛选障碍物数据并将其更新入机载地形高程数据库中。最后,基于三维仿真平台,结合典型算例进行仿真研究。结果表明:该方法能够对前视方向上的城市地形进行有效探测并准确更新,可用于保障直升机城市内飞行安全。

倾转旋翼机过渡状态飞行速度对气动性能的影响

针对倾转半机翼类型的倾转旋翼机,采用计算流体力学方法建立过渡状态的数值计算模型,用于其气动特性计算与分析,研究前飞速度对倾转旋翼机过渡状态气动性能的影响。首先,基于动量源方法建立旋翼气动分析模型,对孤立旋翼进行动压分布计算并与试验结果进行对比,验证建立的动量源方法的有效性;然后,建立全机的气动干扰数值计算模型,对机身采用非结构化网格进行划分;最后,分析过渡状态主要部件竖直方向力及倾转段机翼气动性能随前飞速度的变化规律。结果表明:随倾转角增大,倾转段机翼的升阻比减小明显;在小倾转角度下,虽然倾转段机翼发生了失速,但由于其迎风面积增大且在升力方向上具有一定的投影面积,其升力不会迅速减小。

Research on Aerodynamic Characteristics of Hovering Rotor Based on Leading Edge Droop

In view of the reduction of hovering efficiency near high tension when a helicopter rotor hovers,a numerical simulation method of lifting rotor hovering aerodynamic characteristics based on leading edge droop is established in this paper. It is dominated by Reynolds average N-S equation in integral form. Firstly,VR-12 airfoil is taken as the research object,and the influence of leading edge droop angle on the aerodynamic characteristics of two-dimensional airfoil is studied. Secondly,the modified 7 A rotor is taken as the research object,and the effects of different leading edge droop angles at the position of blade r/R=0.75—1 on the aerodynamic characteristics in hover are explored. It is found that the leading edge droop can significantly improve the aerodynamic characteristics of two-dimensional airfoil and three-dimensional hovering rotor near high angle of attack,and can effectively inhibit the generation of stall vortex.

基于黏性涡粒子和非定常面元法耦合的倾转四旋翼飞行器气动干扰研究

为研究倾转四旋翼飞行器复杂的气动干扰问题,首先基于黏性涡粒子和非定常面元法建立了倾转四旋翼飞行器干扰流场的数值计算方法,并验证了该方法的有效性;其次,根据建立的方法对悬停和前飞状态下的气动特性和干扰情况进行了计算和分析;最后,针对干扰情况对倾转四旋翼的气动布局进行了部分优化设计。结果表明:悬停时的干扰主要来自旋翼下洗流对机翼作用产生的向下载荷,占旋翼拉力的25.3%;前飞时的干扰主要表现为旋翼尾流对机翼“增阻”作用,致使全机升阻比降低13.2%,增加前后旋翼的横向间距能使前飞时后旋翼的拉力和效率分别提升13.5%和4.2%,全机的升阻比提高3.1%;旋翼下方机翼后缘向下偏转的布局能使悬停时机翼受到的向下载荷减小40.7%。

变直径倾转旋翼机设计重心包线研究

倾转旋翼机具有直升机垂直起降和固定翼高速前飞的特点,而变直径倾转旋翼机可以同时满足其悬停和巡航状态对旋翼的设计要求。基于飞行动力学模型,提出一种倾转旋翼机重心极限及设计重心包线计算方法。以XV-15进行方法验证,分析了旋翼变直径对全机重心包线的影响。结果表明,大直径有利于扩大直升机模式和过渡状态的重心包线,而直径变化对固定翼飞机模式重心包线无影响。

Numerical Study on Influence of Key Parameters of Aerodynamic Characteristics of Shaftless Ducted Rotor

Shaftless ducted rotor(SDR)is a new type of ducted rotor system designed with ducted-rotor-motor integration,which is quite different from traditional ducted rotor(DR)in aerodynamic characteristics.The sliding mesh based on unstructured grid is used to simulate the aerodynamic characteristics of SDR and DR.Then,the effects of five key parameters,namely,the rotor disk height,the number of blades,the spread angle of the duct,the central hole radius and the ducted lip radius on the aerodynamic characteristics of the SDR are investigated.It is found that the same-sized SDR produces a larger total lift than the DR in hovering,but the lift proportion of its duct is reduced.In the forward flight,a large low-speed region is generated behind the SDR duct,and the reflux vortex in blade root above the advancing blade has the trend for inward diffusion.The rotor disk height has similar effects on SDR and DR.Increasing the number of blades can effectively increase the total lift of SDR,which also increases the lift proportion of duct.Increasing the spread angle of the duct will lead to the rotor lift coefficient decrease,reducing the central hole radius can increase the total lift,but the component lift coefficient decreases.Appropriately increasing the ducted lip radius can increase the total lift,which begins to decrease after reaching a certain value.

Structural Dynamic Optimization for Flexible Beam of Helicopter Rotor Based on GA

As one of the most important steps in the design of bearing-less rotor systems,the design of flexible beam has received much research attention.Because of the very complex working environment of helicopter,the flexible beam should satisfy both the strength and dynamic requirements.However,traditional optimization research focused only on either the strength or dynamical characteristics.To sufficiently improve the performance of the flexible beam,both aspects must be considered.This paper proposes a two-stage optimization method based on the Hamilton variational principle:Variational asymptotic beam section analysis(VABS)program and genetic algorithm(GA).Consequently,a two-part analysis model based on the Hamilton variational principle and VABS is established to calculate section characteristics and structural dynamics characteristics,respectively.Subsequently,the two parts are combined to establish a two-stage optimization process and search with GA to obtain the best dynamic characteristics combinations.Based on the primary optimization results,the section characteristics of the flexible beam are further optimized using GA.The optimization results show that the torsional stiffness decreases by 36.1%compared with the full 0°laying scheme without optimization and the dynamic requirements are achieved.The natural frequencies of flapping and torsion meet the requirements(0.5 away from the passing frequencies of the blade,0.25 away from the excitation force frequency,and the flapping and torsion frequencies keep a corresponding distance).The results indicate that the optimization method can significantly improve the performance of the flexible beam.