浅析GPS信号干扰对飞机运行的影响

现代飞机GPS系统的作用越来越重要,同时GPS信号干扰的相关报告也越来越多,GPS信号干扰严重影响飞机运行和航空安全.本文通过实例剖析了GPS信号干扰产生的原因、对其他功能的影响及相关的驾驶舱效应,并提出建议处置措施,以帮助相关人员及时识别和排除干扰信息,提高排故效率、缩短排故时间,保障飞行安全.     

农林飞机近地作业飞行的横航向稳定特性

 分析了地面效应对飞机产生附加滚转和偏航力矩的气动新机理,研究了农林飞机近地作业飞行时横航向气动特性随高度的变化规律,推导了考虑地面效应影响时的飞机横航向静稳定性新准则,并分析了不同飞行高度时这些静稳定性的变化趋势。采用地效区内飞机的运动方程,计算并分析了农林飞机不同作业高度下的横航向模态特性及变化规律,并进行了模态特性的简化和验证分析。     

俯仰振荡翼型推阻力转变滞后机制数值研究

扑翼产生的反卡门涡街被认为是一种推力型尾迹,但已有研究指出,随着斯特劳哈尔数(St)增大,低雷诺数下俯仰振荡翼型的净推力产生明显滞后于反卡门涡街的出现。为探究该现象背后的物理机制,对NACA0012翼型在雷诺数1 000条件下作简谐俯仰运动的流场进行了数值模拟。采用翼型表面积分方法和基于有限控制体的气动力估计方法分别研究了翼面分布力特性和尾迹流场特性变化对阻力-推力转变临界点的影响。翼面分布力积分结果表明,当翼型振荡参数进入对应反卡门涡街尾迹形态区域时,翼面压力分布产生的推力分量无法克服剪切层的黏滞阻力,是造成俯仰翼型推力产生滞后于反卡门涡街出现的主要原因。对尾迹流场及相应的推阻力特性变化的分析表明,尽管反卡门涡街会产生"喷流效应",但在St较小时,其产生的动量诱导推力无法克服反卡门涡自身的涡致阻力和尾迹流场压力损失引入的附加阻力,因此即使存在反卡门涡街也不能产生净推力,进而从流场分析的角度进一步解释了这一滞后现象的发生机制。     

基于acetone-PLIF技术的超燃冲压发动机燃烧室燃料/空气掺混特性

针对超燃冲压发动机燃烧室内燃料/空气掺混特性,设计了一套以acetone-PLIF(planar laser-in-duced fluorescence)为技术手段的流动显示测量系统,得到了4种不同结构交错楔形支板在不同特征截面处的丙酮荧光图像,研究了喷嘴位置和尾缘角这两个变量对燃料/空气掺混效果的影响.结果 表明:"...     

振动试验夹具边界效应的动力学分析

振动试验夹具的边界效应是影响振动试验模拟精度的主要因素之一。忽略试验件与试验夹具之间的动力学作用,应用振动台的基础激励来模拟实际的振动环境,其结果的有效性依赖于工作状态的振动边界和试验状态的振动边界在多大程度上满足无限大阻抗输入模型假设。文章提出了一种分析夹具边界效应的有效方法,该方法来源于结构动力学分析的子结构方法,将包含夹具在内的试验系统的动力学特性表述为子结构动力学特征参数描述的标准特征值问题,通过特征频率与振型的比较,评价夹具的边界效应。数值模拟展示了分析过程,并验证了该方法的实用性。     

磁场重联中的哨声波与Hall效应

数值研究Hall电流效应对于重联动力学特征及波动特性的影响.结果表明,具有强Hall效应的算例,重联出流区张角大,重联率高.对于不同Hall效应的算例,应用快速傅里叶变换(FFT),将平面外磁场By分量和(x,z)平面内的速度分量vx,vz位于给定点的时间序列转换为功率谱,并对电场E采用最小方差分析法,确定波的传播方向与偏振特性.研究发现,在强Hall效应的算例中,磁分界线附近存在具有典型特征的哨声波,Hall效应减弱,则波动信号减弱.上述结果表明,Hall电流效应对重联动力学特征具有重要影响,是产生哨声波和快速重联率的关键因素;此外,对于强Hall效应的算例,磁分界线附近哨声波幅度与平面内场向电流Jp间存在正相关关系,它从另一个侧面展示了哨声波与Hall效应间的重要联系.      

多孔径穿孔板控制液雾燃烧不稳定的研究

研究了一种带可调背腔的多孔径穿孔板声阻尼器的吸声特性,并通过声学模型预测了穿孔板的吸声特性.实验研究了偏流穿孔板对液雾燃烧器的燃烧室、气室内波动的动态压力及热释放率的控制效果.多孔径穿孔板存在两种孔径:小孔半径均为1.0mm,大孔半径分别为1.5、2.0、2.5、3.0mm.发现孔径差异过大的穿孔板消声性能不佳.但是大...     

航空发动机风扇叶片吞冰损伤数值模拟方法

文中建立了航空发动机吞冰进气损伤虚拟试验验证模型。系统研究了冰体的本构模型及叶片损伤模型,基于冰撞击过程计算过程建立了一套叶片吞冰损伤规范化分析方法和专业化软件系统。基于该方法可以为航空发动机进气条件下的吞冰损伤物理试验提供多方案快速优化的数值参考,可有效节约试验成本、提升试验效率。     

An improved prediction model for corner stall in axial compressors with dihedral effect

Corner stall predictions are important and difficult in axial compressors. However, all of the prediction models have proved to be ineffective for advanced compressor blades, which tend to use the combined sweep and dihedral. As for the prediction parameter DL, although it effectively modeled the effects of the adverse pressure gradient and secondary flow, it failed to predict the corner stall of curved blades because the model failed to consider the intersection of the boundary layer at the corner region. In this paper, the shape factor gradient Ψ of the boundary layer at the corner region was investigated by numerically studying specially shaped expansion pipes under different adverse pressure gradients. The improved prediction parameter DJ was presented based on the model of Ψ and the circumferential pressure gradient ξ. A comparison of the critical range of the prediction parameters DL and DJ was investigated using the NACA65 cascade database, which was established by a numerical method. Then, the stall criterion was validated according to the experimental results of various test facilities with different blade geometries and experimental conditions. The results show that the improved prediction parameter is able to predict the corner separation/stall flows and is in good agreement with the experimental results for axial compressors with three-dimensional designed blades.     

Experimental of combustion instability in NTO/MMH impinging combustion chambers

This paper presents an experimental study into dynamics of chamber pressure and heat release rate during self-excited spinning and standing azimuthal mode in NTO/MMH (nitrogen tetroxide/monomethylhydrazine) impinging combustion chambers. Nine cases including two combustion chamber configurations were conducted. The operating conditions of all unstable cases were located in the instability region according to Hewitt empirical correlation. The results show that chamber pressure oscillations keep pace with the corresponding OH* chemiluminescence intensity over the whole combustion region in the spinning and standing modes. It is indicated that the Rayleigh index is positive over the whole combustion area in all the unstable cases. A significant supersonic flame front structure of the first-order spinning mode was found in a cylindrical chamber, which means that a detonation wave could exist in the cylindrical chamber without a center body. The pressure and heat release rate oscillations at the pressure node are nonnegligible although their amplitudes are lower than those at the pressure antinode in the first-order standing mode with an annular chamber. Besides, the dominant frequency of pressure and heat release rate oscillations at the pressure node is twice as high as that at the pressure antinode.