航空发动机中冰晶结冰的研究进展

一般认为经过风扇压缩后空气温度高于冰点,压气机内不会发生结冰。然而近年来,国外研究者对若干起发动机推力损失故障的研究表明冰晶能够引起压气机内部结冰,并在试验室中再现了温度高于冰点时压气机内结冰这一现象。我国在航空发动机冰晶结冰研究方面刚刚起步,为准确掌握国内外研究现状,从数值和试验两方面对国内外已开展的压气机内结冰研究进行了分析与总结,讨论了当前冰晶结冰的主要研究成果和存在的局限,提出了开展冰晶结冰研究需重点关注的方向,为我国航空发动机冰晶摄入结冰研究和适航审定研究提供一定参考。     

WAKE GEOMETRY CALCULATIONS FOR TILT-ROTOR USING VISCOUS VORTEX METHOD

A tilt-rotor unsteady flow analytical method has been developed based upon viscous vortex-particle meth- od. In this method, the vorticity field is divided into small assembled vortex particles. Vortex motion and diffusion are obtained by solving the velocity-vorticity-formed incompressible Navier-Stokes equations using a grid-free La- grangian simulation method. Generation of the newly vortex particles is calculated by using the Weissinger-L lifting surface model. Furthermore, in order to significantly improve computational efficiency, a fast multiple method （FMM） is introduced into the calculation of induced velocity and its gradient. Finally, the joint vertical experimen- tal （JVX） tilt-rotor is taken as numerical examples to analyze. The wake geometry and downwash are investigated for both hover and airplane modes. The proposed method for tilt-rotor flow analysis is verified by comparing its re- sults with those available measured data. Comparison indicates that the current method can accurately capture the complicated tilt-rotor wake variation and be suitable for aerodynamic interaction simulation in complex environ- ments. Additionally, the aerodynamic interactional characteristics of dual-rotor wake are discussed in different ro- tor distance. Results show that there are significant differences on interactional characteristics between hover mode and airplane mode.     

SIMULATION OF COMPOSITE NON-LINEAR MECHANICAL BEHAVIOR OF CMCS BY FEM-BASED MULTI- SCALE APPROACH

The non-linear behavior of continuous fiber reinforced C/SiC ceramic matrix composites （CMCs） under tensile loading is modeled by three-dimensional representative volume element （RVE） models of the composite. The theoretical background of the multi-scale approach solved by the finite element method （FEM） is recalled first- ly. Then the geometric characters of three kinds of damage mechanisms, i.e. micro matrix cracks, fiber/matrix interface debonding and fiber fracture, are studied. Three kinds of RVE are proposed to model the microstructure of C/SiC with above damage mechanisms respectively. The matrix cracking is modeled by critical matrix strain en- ergy （CMSE） principle while a maximum shear stress criterion is used for modeling fiber/matrix interface debond- ing. The behavior of fiber fracture is modeled by the famous Weibull statistic theory. A numerical example of con- tinuous fiber reinforced C/SiC composite under tensile loading is performed. The results show that the stress/ strain curve predicted by the developed model agrees with experimental data.     

WIFI AIDED INTEGRITY IMPROVEMENT IN MEMS INS/GNSS INTEGRATION

The reliability of global navigation satellite system （GNSS） positioning degrades when satellite signals are interfered. Such degradation is hard to be deteced by a micro-electro mechanical system （MEMS） based inertial system（INS）/GNSS, integrating navigation system with a conventional Kalman filtering, which results in poten- tial integrity problem of the system. Hence, an algorithm combining wireless fidelity （WiFi） signal with a federa- ted Kalman filter （FKF） is proposed to identify the system integrity in dense urban navigation. The criterion of the system integrity detection is created followed by the derivation of the integrity coefficient. The field test shows that integrity changes can be captured by applying WiFi, and the maximum positioning error is reduced by 67~ without compensation of inertial sensors in integrity deterioration.     

仿鞭毛菌游动的微型机器人近壁运动

鞭毛菌及模仿其运行的微机器人在靠近壁面游动时,其运动模式与远离壁面时有所不同。针对这一现象,本文利用抗力理论和Stokes方程的线性性质,对鞭毛菌在壁面附近运动时流体对其施加的作用力进行分析,建立了鞭毛菌近壁运动的动力学模型。同时计算了细菌在平行于壁面平面内的运动轨迹与游动速度,并与实验数据进行对比分析,结果验证了该理论模型 的有效性。在此基础上,探讨了鞭毛尾的几何和运动学参数与细菌的速度变化量之间的关系。本文研究为微型仿生游动机器人运动控制时规避近壁效应提供参考依据。     

考虑非理想噪声干扰的直升机飞行动力学模型辨识方法

利用MATLAB/SIMULINK平台搭建了直升机仿真实验系统,并以UH-60直升机为对象实现了考虑非理想噪声干扰的仿真飞行实验。建立了非理想噪声数学模型并基于增广最小二乘法设计 了一套同时考虑模型参数和噪声参数的综合辨识算法,在此基础上,利用仿真实验数据实现了UH-60直升机纵向飞行动力学模型的辨识与验证。最后,通过与普通最小二乘法的对比验证了本文方法的优越性。      

时变支承刚度对分流传动系统振动特性的影响

基于集中质量法,考虑时变啮合刚度、综合传递误差和齿侧间隙等因素的影响,建立了圆柱齿轮分流传动系统的弯扭耦合动力学模型和方程。采用变步长Runge-Kutta法,对动力学方程进行了数值求解;通过引入滚动轴承的支承刚度计算模型,分析了时变支承刚度和非时变支承刚度对系统振动特性的影响。仿真结果表明：当按照时变支承刚度模型计算时,轴承的支承刚度会产生4%左右的波动,输出轴上的横向振动位移幅值增大了约5%;支承刚度的时变性使得系统的非线性增强,稳定性变差;支承刚度的时变特性对分扭级动载系数影响较大,对并车级动载系数影响较小。     

软管-锥套式空中加油动态建模与性能分析

提出了一种基于凯恩方程的自主空中加油软管-锥套动态模型及性能分析方法。该方法将软管视为由有限段以铰链形式连接的刚性 杆组成,锥套为软管末端的一个质点。本文定义了描述系统状态的广义坐标及广义速率,导出了软管段位置多级递推公式和系统动态方程,估算了软管在加油机尾流、定常流和大气扰动下的气动载荷。通过数值仿真分析了平稳大气中锥套在加油机不同飞行条件下的稳态阻力和软管拖拽轨迹,验证了模型的正确性及系统稳定性。最后研究了大气扰动对锥套运动的影响及不同软管段的受扰运动。     

用于捕获轨迹风洞试验的三自由度转角头设计

设计了用于FL-12风洞捕获轨迹试验的三自由度转角头装置,该装置为机电一体化设备。介绍了三自由度转角头装置的结构设计,控制系统设计,驱动元件的选型计算及校核,并对装置进行了静力学与动力学分析以验证设计结果。结果表明,和现有装置相比,该三自由度转角头在俯仰和偏航方向的载荷能力均由100N·m提升至250N·m,可控制精度由0.1°提升至0.05°,在滚转方向的载荷能力由10N·m提升至20N·m,可控制精度由0.1°提升至0.05°。通过对试验装置风洞适用性的研究,在设计中对驱动元件及线缆的结构、整流装置的外形、装置总体尺寸等进行了优化,改善了现有设备线缆外露,外形整流性能较差以及风洞堵塞比较大等问题。     

过冷大水滴变形及阻力特性的温度影响实验研究

为探索温度对过冷大水滴(SLD)变形及阻力特性的影响规律,在常温和低温环境下开展了过冷大水滴动力学特性的实验研究。研究表明:过冷大水滴在快速加速气流中运动时,水滴变形特征和阻力特性随We 数的变化规律主要分为3个阶段:波动阶段、阶跃阶段和平滑阶段,并会受到低温环境的影响;同一We 数的水滴变形率、阻力系数会呈现出随着温度的降低而降低的趋势;温度对处于波动阶段的过冷水滴影响最大,随后在阶跃和平滑阶段,温度对水滴动力学行为的影响逐渐减小。