【作者】 李攀；

【导师】 陈仁良；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2010， 博士

【摘要】 旋翼非定常气动力建模以及旋翼与直升机其它部件的气动干扰建模一直是影响直升机飞行动力学数学模型置信度的“瓶颈”。围绕这一问题,本文以建立高置信度的直升机飞行动力学模型为目标,对适用于过渡和机动飞行的旋翼非定常自由尾迹模型及其对直升机飞行动力学建模方法和准确性的影响进行了深入的研究。发展了适用于机动飞行的旋翼非定常自由尾迹模型。以升力面法和涡方法为理论基础,建立了兼顾效率和准确性的桨叶升力面模型及其尾迹描述方法,包括了一个新的旋翼桨尖涡卷起模型,通过桨叶载荷(环量)分布来计算桨尖涡的初始涡核半径、展向位置和环量,以消除依靠经验来设定这些物理量的现状。针对旋翼非定常自由尾迹模型遇到的数值问题,发展了一种新的数值稳定、高效的时间步进差分算法(CB2D),重点考查了该算法用于自由尾迹控制方程求解的数值稳定性,以保证解的物理正确性。建立了基于非定常自由尾迹模型和翼型非定常/动态失速模型的旋翼气动力模型用于研究机动飞行中旋翼的非定常气动特性。为了验证该模型,利用旋臂机上的模型旋翼进行了机动飞行实验研究,分别测量了悬停和低速飞行条件下总距、周期变距以及旋翼轴角速度突增时旋翼载荷的瞬态响应。通过测量数据与计算结果的对比,验证了旋翼气动力模型和非定常自由尾迹模型的有效性。结果表明旋翼尾迹的各种动态畸变对桨盘入流、旋翼载荷的瞬态特性有重要影响;旋翼轴作角运动时,尾迹弯曲畸变引起的桨盘入流梯度与尾迹弯曲曲率并非简单的正比关系。在此基础上,发展了一套新的综合的直升机飞行动力学模型,集成了机体六自由度刚体模型、旋翼模型、旋翼对机身、尾翼的气动干扰模型以及发动机/燃油调节系统模型,其中旋翼模型包括了挥舞-摆振-扭转耦合的非线性弹性桨叶动力学模型、非定常自由尾迹模型和翼型非定常/动态失速模型。给出一种数值方法将旋翼/机体耦合运动方程转换为显式一阶常微分方程的形式,以便于采用标准的算法进行求解和计算效率的提高。针对综合的直升机飞行动力学模型分别建立了配平计算方法和动态响应计算方法。在配平计算中,旋翼自由尾迹模型与旋翼/机体动力学模型采用松耦合的方式进行迭代求解;在动态响应计算中,建立了自由尾迹CB2D时间步进算法与旋翼/机体动力学方程求解算法之间的协调机制,两者以强耦合的方式沿时间推进。为验证综合模型的有效性,以UH-60A直升机为例,进行了定常平飞配平计算以及右压杆、急拉杆机动飞行的动态响应计算。计算结果与飞行实测数据的对比表明,旋翼自由尾迹模型和气动干扰效应对直升机飞行动力学模型的置信度有重要影响,而桨叶的弹性变形效应对铰接式旋翼直升机的模型置信度影响较小;与动态入流模型相比,非定常自由尾迹模型显著提高了悬停和低速飞行状态配平结果的准确性,更准确的预测了直升机的动态响应,尤其是异轴响应。更多还原

【Abstract】 The modeling of rotor unsteady aerodynamics and rotor/fuselage/empennage aerodynamic interaction have been the bottleneck in the high-fidelity mathematical modeling of helicopter flight dynamics. To solve this problem, an unsteady free-vortex wake model for transient or maneuvering flight and its impact on the methodology and accuracy of the modeling of helicopter flight dynamics are investigated in detail in this dissertation.Firstly, an unsteady free-vortex wake model for maneuvering flight is developed. Based on the lifting-surface and vortex methods, the blade aerodynamic model and the method of representating the vortex wake trailed behind the blade are presented with the trade-off between accuracy and efficiency. A new vortex roll-up model which relates the core radius, span station and circulation of the initial tip vortex with the blade bound circulation distribution is deduced for eliminating the empirical parameters in conventional rotor free-vortex models. To solve the numerical problem of unsteady free-vortex wake model, a new time-marching finite-difference algorithm(BC2D) with high efficiency is developed and its numerical stability is examined in detail for physically correct. Then, an unsteady aerodynamic model of rotors based on the unsteady free-vortex wake model and airfoil unsteady aerodynamics with dynamic stall is established to analysis the rotor transient aerodynamics in maneuver flight. To verify the model,a series of tests with model rotor on the Whirling Beam are conducted for the acquisition of the transient responses of rotor loads following the abrupt increases of collective pitch, cyclic pitch and angular rate in both hover and low-speed forward flight. The comparisons of calculated results with test data indicate that the rotor unsteady aerodynamic model developed is effective and there are significant effects of wake dynamic distortion on transient characteristics of rotor inflow and rotor loads. The inflow gradient across the rotor disk induced by the wake curving distortion is not simply proportional to the wake curvature.Furthermore, a new comprehensive model of helicopter flight dynamics is built up, which synthesizes the rigid fuselage motion with 6 degrees of freedom, the rotor unsteady aerodynamics including the flexible blade dynamics with nonlinear flap-lag-torsion coupling, unsteady free-vortex wake and unsteady airfoil aerodynamics with dynamic stall, the effect of rotor/fuselage/empennage aerodynamic interaction as well as the propulsion system dynamics. A numerical method is presented to transform the equations of motion of coupled rotor/ fuselage into first order differential equations with explicit form which can be sovled using standard numerical algorithm with high efficiency.Finally, numerical methods of helicopter trim and dynamic response are developed for the comprehensive model of helicopter flight dynamics. The free-vortex wake dynamics and the coupled rotor/ fuselage dynamics are treated with loose coupling for trim analysis but with tight coupling for response calculation. To validate the comprehensive model, the UH-60A helicopter is taken as an example to predict the trim characteristics and dynamic responses in maneuvering flight. The comparisons of calculated results with flight test data indicated that there is great effect of the free-vortex wake dyanmics and aerodynamic interaction on the fidelity of comprehensive model while the effect of the flexible blade dynamics is small for the helicopter with articulated rotor. Compared with the dynamic inflow model, the unsteady free-wake model improves the accuracy of trim results in hover and low-speed forward flight conditions as well as the dynamic responses in maneuvering flight, especially off-axis responses.更多还原