低(变)湍流度风洞设计再探讨

在资料调研与总结国内约20年来成功研制低(变)湍流度风洞的基础上,介绍了这类风洞设计思想中几点有新意的方法,供设计者参考.对减湍起决定作用的稳定段布局设计给出了一组综合性图线;对减湍起重要作用的收缩段设计提出了通用便捷的方法;对全系统起优化作用的风扇动力段及拐角导流片设计研制等有一定的新见解.     

Modeling turbulent transport effects on kernel formation and ?ame propagation in an ignition process

Reliable relighting is crucial for advanced low-emission aero-engine combustors. For forced ignition under highly-turbulent conditions, eddies of sizes being smaller than the flame kernel can affect its formation through penetrating and modifying the kernel structure. In this study, a one-dimensional model for small-scale turbulence on kernel formation is developed through the incorporation of turbulence-induced diffusion in governing equations. With given flow conditions,the spatial and time-dependent turbulent diffusivity is modeled using the idea of residual eddy viscosity. One-dimensional spherical flames of premixed pre-vaporized n-dodecane/air mixtures under high-altitude conditions are simulated to investigate the effects of turbulence. It is revealed that the range of the equivalence ratio for successful turbulent ignition is much narrower than that for laminar ignition. The range decreases with an increased turbulent intensity, and this effect is more pronounced for a low spark energy. In addition, turbulent transport has more pronounced effects on rich mixtures. An analysis on energy budget and species profiles shows that turbulence-induced diffusion enhances the heat loss at the very beginning of the kernel formation process that could lead to ignition failure. After the flame kernel is established, turbulent transport broadens the flame front, enhances the heat release rate, and thereafter increases the flame propagation speed.     

Stiffeners layout design of thin-walled structures with constraints on multi-fastener joint loads

The purpose of this paper is to present an extended topology optimization method for the stiffeners layout design of aircraft assembled structures.Multi-fastener joint loads and manufacturing constraints are considered simultaneously.On one hand,the joint loads are calculated and constrained within a limited value to avoid the failure of fasteners.On the other hand,the manufacturing constraints of the material distribution in the machining directions of stiffeners are implemented by an improved piecewise interpolation based on a beveled cut-surface.It is proven that the objective function is strictly continuous and differentiable with respect to the piecewise interpolation.The effects of the extended method with two different constraints are highlighted by typical numerical examples.Compared with the standard topology optimization,the final designs have clearly shown the layout of stiffeners and the joint loads have been perfectly constrained to a satisfying level.     

含间隙天线折展机构模块精度分析

针对天线折展机构连接运动副间隙引起天线折展过程运动不确定、精度下降等问题,提出了基于"无质量杆"模型来模拟自由状态的含运动副间隙机构建模方法。该方法基于D-H法建立了天线3个闭环的几何关系模型,将无质量杆模型引入天线几何关系中,获得了展开误差的计算模型。通过综合运用蒙特卡洛法实现了自由状态折展机构展开误差计算。计算结果表明:转动副间隙对折展机构单元肋展开在Z方向上展开精度影响最大,单元肋展开最大误差为0.353 mm,可为天线折展机构设计提供了参考。     

液体火箭发动机针栓喷注器雾化燃烧技术研究进展

针栓喷注器具有结构简单、可靠性高、燃烧稳定,可实现深度节流、面关机、机构可按比例缩放、成本低等显著优点,以其为基础的推力调节技术是一种实现液体火箭发动机变推力方案的有效途径,得到了广泛的应用。基于国内外针栓喷注器及针栓式发动机技术的发展现状和应用实例,着重从喷注器雾化性能和发动机燃烧流动问题2个方面进行了分析,在此基础上提出了对喷注器及发动机技术研究方向和研究重点的建议。     

2219薄板铝合金浮动式双轴肩搅拌摩擦焊接及组织性能分析

以运载火箭助推器贮箱广泛应用的4 mm厚2219薄板铝合金为焊接对象,研制了浮动式双轴肩搅拌头,分析了内部塑性金属流动模式及特点,并推测出需匹配较低焊接热输入才能获得优质焊缝。工艺探索及优化试验结果直接验证了焊缝内部塑性金属流动模式及推测。接头宏观组织形貌分析结果显示:不同焊接速度下的焊缝横截面宏观形貌都可以观察洋葱环特征,且随着焊接速度提高,洋葱环特征越发增多,并从靠近前进侧的焊核区逐渐向后退侧孕育发展,这也有效验证了薄板铝合金双轴肩搅拌头的设计思路。薄板铝合金双轴肩搅拌摩擦焊接头横截面显微硬度分布均呈"U"型,接头显微硬度最低点位于焊核区与后退侧热机影响区的交界处。接头力学性能测试结果显示:随着焊接速度逐渐升高,接头抗拉强度逐渐升高,且当焊接速度达到350 mm/min时,接头抗拉强度达到最高值。铝合金浮动式双轴肩搅拌摩擦焊接头延伸率整体较高,焊接速度对其影响不大。铝合金双轴肩搅拌摩擦焊接头正、背弯均可以达到180°无裂纹。基于立式纵缝搅拌摩擦焊系统成功实现了2 m长试片的浮动式双轴肩搅拌摩擦焊,累计焊接长度达到60 m,且双轴肩搅拌头完整,未发现裂纹、扭曲或其他损伤。     

脉冲超宽带信号测量性能分析

超宽带技术是一项新兴的无线通信技术,具有极其广阔的发展前景,但目前仅用于室内短距离通信,少见用于航天测控系统。为了将超宽带技术应用于测控系统中,以模糊函数为工具,对脉冲超宽带信号的测量性能进行分析。首先推导矩形脉冲串信号和载波调制矩形脉冲串信号的模糊函数,并对其模糊特性进行仿真分析。在此基础上,主要针对用于测控系统的伪码调制脉冲超宽带信号,利用其模糊函数分析其测距测速性能。结果表明:该超宽带信号具有良好的测距测速性能,其最大无模糊距离为1个伪码周期,最大无模糊多普勒频率为脉冲重复频率的倒数;单脉冲宽度越窄,其测距性能越好而测速性能越差。     

大跨度悬索桥钢箱主梁涡振性能优化风洞试验研究

以某大跨度钢箱梁悬索桥为工程背景,该桥桥面高速公路与人行道并存,桥面栏杆较多,且设置了防抛网,主梁竖向及扭转涡振明显.通过节段模型风洞试验研究了检修车轨道位置、桥面栏杆、分流板以及攻角和阻尼等对主梁涡激振动性能的影响,提出了优化主梁涡振的气动措施.试验结果表明,优化检修车轨道位置和在主梁风嘴处设置分流板能有效地抑制主梁涡振.     

涡轮风扇发动机紧凑压缩系统气动性能

通过数值方法研究了由2级风扇、4级高压压气机及外涵组成的紧凑压缩系统的气动性能.探讨了双涵双轴压缩系统气动性能的评估方法及数值计算中相应的边界给定方法.通过对紧凑压缩系统的一体化数值模拟,分别获取了风扇及高压压气机的设计转速特性,并与设计值进行了对比,结果表明流量、压比、效率都达到了设计要求,而风扇失速裕度仅为7.8%...     

航空发动机高温部件系统模拟技术

对航空发动机高温部件系统模拟技术进行研究,在涡轮等高温部件及其冷却系统组成的流固系统研究中采用整体域划分思路,并对两部分组成的整体域统一求解.将该方法在某模型中进行分析验证,应用到某涡轮系统及周围冷却空气模拟中,并对强弱耦合两种耦合模拟方法的结果进行了比较分析.