超燃燃烧室等离子体点火和火焰稳定性能

为了研究热等离子点火器在超燃冲压发动机中的应用,在来流马赫数2.0工况下,针对乙烯和氢气两种燃料,进行了超燃环境中等离子体点火的试验和仿真研究.在来流总温1 500~1 950 K,燃料当量比0.1~0.55范围内对等离子点火器的点火和改善燃烧性能的性质进行了详细分析.结果显示:对于氢气和乙烯燃料,等离子体点火器使两种燃料的点火性能均得到明显改善,点火延迟时间大大缩短,燃料着火范围扩大、贫燃极限当量比降低.但未观察到其在加速掺混以及改善燃烧性能方面的明显作用.进行了与乙烯燃烧试验对应的数值仿真工作,选用了两种乙烯化学反应模型进行对比研究.仿真结果显示:8步9组分反应模型与试验结果符合较好,而3步6组分反应模型过高的估计了反应剧烈程度,燃烧室压力值偏高,压力起始上升位置偏向上游.所用的8步模型比3步模型更适合于超燃燃烧室中乙烯反应的模拟.     

湍流边界层相干结构空间拓扑形态的 层析TRPIV测量

用层析TRPIV(time-resolved paticle image velocimetry)技术精细测量了水洞中平板湍流边界层三分量速度的时空序列信号,提出了空间局部平均多尺度速度结构函数的新概念描述湍流多尺度涡结构的空间拉伸、压缩、剪切变形和旋转.用空间局部平均多尺度速度结构函数对湍流脉动速度进行了空间多尺度分解.用空间局部平均多尺度速度结构函数的新概念,根据湍流多尺度涡结构在空间流向的拉伸和压缩特征,提出了新的湍流相干结构条件采样方法,检测并提取了层析TRPIV数据中相干结构的“喷射”和“扫掠”事件中的速度、涡量等物理量的空间拓扑形态.发现在喷射和扫掠事件中均存在一对反向旋转的准流向“马蹄形”涡结构.      

超声速反应流火焰面/进度变量模型

基于Pierce低马赫数条件下的火焰面/进度变量模型,考虑可压缩性和激波的影响,发展了用于超声速湍流反应流的火焰面/进度变量模型.该模型通过求解混合分数和进度变量两个标量方程来描述化学反应,且采用火焰面方程解的完整的三个分支:稳态燃烧分支、具有局部熄火状态的非稳态分支和完全熄火分支.利用该模型对德国宇航中心(DLR)的超燃冲压发动机进行模拟,与稳态火焰面模型得到的附着火焰不同,计算结果捕捉到了熄火和火焰抬举现象;且数值阴影和平均温度分布与实验结果吻合较好.      

一种改进的类DES湍流模拟方法

构造了一种基于一方程S-A(Spalart-Allmaras)模型和一方程Yoshizawa亚格子模型的混合RANS/LES(Reynolds-averaged Navier-Stokes/large eddy simulation)湍流模拟方法.在涡黏假设的基础上,将Yoshizawa亚格子湍动能方程转化为等效的亚格子湍流涡黏性输运方程,并采用混合函数将其与S-A模型方程进行混合,从而改进了DES(detached eddy simulation)模型的亚格子行为,同时克服了其依靠网格控制模型转换的缺点.模拟了超声速的带斜坡凹腔流动,并与相同网格下的LES及DES结果进行了比较,结果表明该混合RANS/LES方法在远离壁面的自由剪切流区域与LES行为一致,而在附着边界层区域表现优于LES和DES方法.      

超音速、高超音速飞行器动导数的高效计算方法

将超音速、高超音速气动力工程计算方法综合起来,推广到非定常气动力的计算,并用于求解任意外形飞行器作强迫运动时的非定常气动力.在此基础上进一步发展了一种适合于超音速、高超音速大迎角状态的飞行器动导数计算方法和程序.计算结果与国际标准实验数据作了比较,证明了该程序的正确性和精度.研究了减缩频率和基本迎角对动导数的影响,结果表明基本迎角对动稳定性导数影响较大,而减缩频率在小迎角范围内对动导数影响很小.     

基于凹槽火焰稳定器的煤油超声速燃烧试验

在直联式超声速燃烧试验台上进行了煤油的超声速燃烧试验,使用了4种不同结构的凹槽火焰稳定器和多种直径的煤油喷嘴,煤油当量比0.24~1.32,引导氢当量比0.53,在多种工况下均实现了煤油的成功点火和稳定燃烧.通过测量燃烧室壁面静压分布比较不同工况下煤油燃烧性能.研究发现:凹槽结构对煤油的点火性能影响较大,较大的凹槽长深比更有利于煤油的点火,部分凹槽能在无引导氢条件下实现煤油自燃点火;试验中使用的4种凹槽均有较好的火焰稳定效果,煤油燃烧时燃烧室壁面压力平稳;煤油当量比是影响煤油燃烧性能的最主要因素.在煤油当量比相同的条件下,较高的喷注压力能够提高煤油的燃烧性能.      

一种基于多目标决策的超音速民机方案评价方法

以旅客对于超音速民机的需求为出发点,结合人机环境工程中的人体疲劳概念,采用一种基于多目标决策的超音速民机方案评价方法,对超音速民机方案进行评价。将旅客对于旅行快速性、舒适性和经济性方面的要求作为建模的基本属性,建立旅客出行时对于飞机机型选择的多目标决策模型,从市场需求的角度来论证超音速民机方案的可行性。阐述了该可行性方案研究方法的实现原理及建模步骤,并将方法用于新一代超音速民机的初步方案评价中。     

On the early phase of relativistic solar particle events: Are there signatures of acceleration mechanism?

Many physical processes precede and accompany the solar energetic particles (SEP) occurrence on the Earth’s orbit. Explosive energy release on the Sun gives rise to a flare and a coronal mass ejection (CME). X-ray and gamma emissions are believed to be connected with flares. Radio emission is signature of disturbances traveling through the corona and interplanetary space. Particles can gain energy both in the flare and the accompanying wave processes. The beginning of the SEP events has the advantage of being the phase most close to the time of acceleration. Influence of interplanetary transport is minimal in the case of first arriving relativistic solar protons recorded by ground based neutron monitors in so called ground-level enhancements (GLE). The early phase of the SEP events attracts attention of many scientists searching for the understanding of particle acceleration. However, they come to the opposite conclusions. While some authors find arguments for coronal mass ejections as a sole accelerator of SEPs, others prove a flare to be the SEP origin. Here, the circumstances of SEP generation for several GLEs of the 23rd solar cycle are considered. Timing of X-ray, CME, and radio emissions shows a great variety from event to event. However, the time of particle ejection from the Sun is closer to maximum of X-ray emission than to any other phenomena considered. No correlation is found between the particle fluxes and the CME characteristics.     

超声速空腔流激振荡与声学特性研究

基于高速风洞试验研究了超声速时空腔流激振荡与声学特性.试验马赫数为1.5,基于每米的雷诺数为2.26×107,来流边界层厚度为0.024 m,试验空腔长深比分别为15,12和6.结果表明:空腔内形成的剪切层与腔后壁相撞诱发腔内较强烈噪声,噪声从腔后缘向腔前缘传播时受到腔内流动的干扰,故同频率下腔后缘处的声压均高于腔前中部区域的声压.闭式和过渡式空腔长深比较大,剪切层与腔底面相撞在腔内形成的压缩波或激波,干扰了从腔内声波反馈回路、限制了流激振荡的形成,故腔内未出现明显的声压峰值激振频率;开式空腔长深比较小,剪切层直接跨过空腔中部与腔后壁相撞,产生的噪声向腔前缘传播,腔内形成流激振荡,并出现多个声压峰值激振频率.      

On the relation of the Forbush decreases detected by ASEC monitors during the 23rd solar activity cycle with ICME parameters

To improve the physical understanding of the Forbush decreases (FD) and to explore the Space Weather drivers, we need to measure as much geospace parameter as possible, including the changing fluxes of secondary cosmic rays. At the Aragats Space Environmental Center (ASEC) are routinely measured the neutral and charged fluxes of secondary cosmic rays. Each of species has different most probable energy of primary “parent” proton/nuclei. Therefore, the energy range of the Galactic Cosmic Rays (GCR) affected by Interplanetary Coronal Mass Ejection (ICME) can be effectively estimated using data of the ASEC monitors. We presented relations of the magnitude of FD observed in different secondary particle fluxes to the most probable energy of the primary protons. We investigate the correlations between the magnitude of FD with the size, speed, density and magnetic field of the ICME. We demonstrate that the attenuation of the GCR flux incident on the Earth’s atmosphere due to passing of the ICME is dependent on the speed and size of the ICME and the magnetic field strength.