飞行器气动参数估计不确定度评价方法研究

为了有效地利用飞行器气动参数估计结果,必须同时给出估计结果的不确定度,因此研究了不确定度评价方法.当试验样本较多时,样本标准差具有明确的统计含义,比分散度能够更好地描述参数估计的不确定度.对于单个试验样本,基于不确定度椭球导出的C-R(Cramer-Rao)界是参数估计不确定度最好的理论预测,但利用飞行实测数据得到的C-R界普遍比样本标准差小.鉴于此,通过在低频有色噪声的基础上构造白噪声的方法,得到了一种C-R界修正方法,并通过仿真算例验证了修正方法的正确性.最后,将C-R界修正方法应用于飞行实测数据,得到的修正C-R界与利用多次飞行试验参数估计结果计算的样本标准差比较一致,表明该修正方法能够较好地给出参数估计的不确定度区间.     

Static aeroelastic analysis of very flexible wings based on non-planar vortex lattice method

A rapid and efficient method for static aeroelastic analysis of a flexible slender wing when considering the structural geometric nonlinearity has been developed in this paper. A non-planar vortex lattice method herein is used to compute the non-planar aerodynamics of flexible wings with large deformation. The finite element method is introduced for structural nonlinear statics analysis. The surface spline method is used for structure/aerodynamics coupling. The static aeroelastic characteristics of the wind tunnel model of a flexible wing are studied by the nonlinear method presented, and the nonlinear method is also evaluated by comparing the results with those obtained from two other methods and the wind tunnel test. The results indicate that the traditional linear method of static aeroelastic analysis is not applicable for cases with large deformation because it produces results that are not realistic. However, the nonlinear methodology, which involves combining the structure finite element method with the non-planar vortex lattice method, could be used to solve the aeroelastic deformation with considerable accuracy, which is in fair agreement with the test results. Moreover, the nonlinear finite element method could consider complex structures. The non-planar vortex lattice method has advantages in both the computational accuracy and efficiency. Consequently, the nonlinear method presented is suitable for the rapid and efficient analysis requirements of engineering practice. It could be used in the preliminary stage and also in the detailed stage of aircraft design.     

高超声速气动力及激波位置快速计算方法研究

采用快速计算方法进行高超声速气动力计算时,影响计算精度的关键问题主要在于模型面网格的划分和计算方法的选取。采用一种灵活实用的结构化面网格划分策略,使得模型的各个部件能分别选择合适的计算方法;发展一种基于近似流线的二阶激波膨胀波方法,该方法可以用于多种具有三维流场特性的部件,不仅降低对使用者的经验依赖,还能提高计算精度;配合激波位置计算方法,可以较为准确地计算模型的激波位置,保证边界层外缘参数的计算精度;粘性力计算使用基于起始面元修正的Spalding-Chi方法和参考温度方法。通过对四个典型算例的计算与分析,表明本文发展的高超声速气动力计算方法具有较高的计算精度,能够作为高超声速飞行器初步设计阶段的气动力快速分析工具。     

Panel/full-span free-wake coupled method for unsteady aerodynamics of helicopter rotor blade

A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna-Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics (CFD) results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.     

底部形状对钝锥体模型气动与电磁散射性能的影响

开展了飞行器气动与隐身综合特性数值研究。分别利用时域有限差分法和数值求解N—S方程的方法对飞行器的电磁散射与气动特性进行了数值模拟,研究了钝锥体模型底部形状对其雷达散射截面（RCS）和零升阻力的影响。由数值计算结果可知：合理地改变钝锥体模型底部形状,可以降低模型的RCS。并且,随着椭球体轴的长度或锥体高度的增加,模型的RCS逐渐减小。当飞行马赫数为5．0,高度为20km时,底部形状为椭球体或锥体的模型,随着椭球体轴的长度或锥体高度的增加,模型的零升阻力略有下降。     

高速列车进入隧道产生的微气压波实验研究

高速列车在进出隧道时,会形成压缩波和微压波,引起车厢内压力变化并在隧道出口形成噪声,对乘客及环境造成影响.笔者利用高速列车模型实验系统,对列车进入隧道所形成的压缩波、微压波进行了测试分析,对不同长度喇叭型缓冲结构削减微压波效果进行了比较,得到了有关微压波产生、传播以及缓冲结构缓解微压波效果的规律.     

隧道阻塞比对列车进入隧道产生的气动效应的影响

高速列车在进出隧道时,会形成压缩波和微压波,引起车厢内压力变化并在隧道出口形成噪声,对乘客及环境造成影响.隧道阻塞比对气动效应的产生有非常重要的影响.利用高速列车模型实验系统,对列车进入隧道所形成的压缩波、微压波进行了测试分析,验证了压缩波的隧道阻塞比影响系数值,初步确定了阻塞比与微压波压力的理论关系,依据实验结果,确定了微压波的阻塞比影响系数的范围.     

Aerodynamic optimization of a high-lift system with adaptive dropped hinge flap

The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, ...     

Experimental investigation of expansion effect on shock wave boundary layer interaction near a compression ramp

The experiment is conducted to investigate the effect of expansion on the shock wave boundary layer interaction near a compression ramp. The small-angle expansion with an angle degree of 5° occurs at different positions in front of the compression ramp. The particle image velocimetry and flow visualization technology show the flow structures, velocity field, and velocity fluctuation near the compression ramp. The mean pressure distribution, pressure fluctuation, and power spectral density are me...     

飞行器非定常气动力试验与建模研究

介绍了57°三角翼布局战斗机模型在CARDC直径3.2m风洞进行的俯仰、偏航和滚转3个方向大振幅振荡的非定常气动特性,试验的振幅为20°、35°,俯仰和偏航振荡的减缩频率为0～0.06,滚转振荡的减缩频率为0～0.2。另外利用基于频率域的Fourier变换法和非线性代数法,对非定常气动力建模进行了探讨,气动模型预测结果和试验结果具有较好的一致性。