非恒定增压式微尺度拉瓦尔喷管流动特性

针对微尺度喷流在航天器运动状态切换时出现的非恒定增压变化,采用直接模拟蒙特卡洛(DSMC)方法对阶跃式增压和线性式增压两种模式下的微尺度拉瓦尔喷管流场进行了模拟,并对其变化过程中的流动特性进行了对比分析。结果显示：阶跃式增压会导致流动特性出现较大幅值的峰谷式波动,而线性式增压下的流动特性则呈现出线性变化的特点;黏性力对微尺度喷流的非恒定增压变化产生了重要的黏滞作用,在喉部扩张段至出口的流场中尤为明显;在设定的条件下,阶跃式增压过程中喷流产生的总冲量较线性式增压高59.5%,质量流量高74.7%,单位工质提供的冲量低约8.6%,波动性也高于线性式模型,阶跃式增压适用于系统需要较大推力改变运动状态且推进剂充足的情况,而线性式增压在系统精确微调或需要推进剂产生更高效能时具有明显的优势。     

Survival and death of the haloarchaeon Natronorubrum strain HG-1 in a simulated martian environment

Halophilic archaea are of interest to astrobiology due to their survival capabilities in desiccated and high salt environments. The detection of remnants of salty pools on Mars stimulated investigations into the response of haloarchaea to martian conditions. Natronorubrum sp. strain HG-1 is an extremely halophilic archaeon with unusual metabolic pathways, growing on acetate and stimulated by tetrathionate. We exposed Natronorubrum strain HG-1 to ultraviolet (UV) radiation, similar to levels currently prevalent on Mars. In addition, the effects of low temperature (4, −20, and −80 °C), desiccation, and exposure to a Mars soil analogue from the Atacama desert on the viability of Natronorubrum strain HG-1 cultures were investigated. The results show that Natronorubrum strain HG-1 cannot survive for more than several hours when exposed to UV radiation equivalent to that at the martian equator. Even when protected from UV radiation, viability is impaired by a combination of desiccation and low temperature. Desiccating Natronorubrum strain HG-1 cells when mixed with a Mars soil analogue impaired growth of the culture to below the detection limit. Overall, we conclude that Natronorubrum strain HG-1 cannot survive the environment currently present on Mars. Since other halophilic microorganisms were reported to survive simulated martian conditions, our results imply that survival capabilities are not necessarily shared between phylogenetically related species.     

A comparative and numerical study of effects of gravity waves in small miss-distance and miss-time GPS radio occultation temperature profiles

The Global Positioning System (GPS) Radio Occultation (RO) technique has global coverage and is capable of generating high vertical resolution temperature profiles of the upper troposphere and lower stratosphere with sub-Kelvin accuracy and long-term stability, regardless of weather conditions. In this work, we take advantage of the anomalously high density of occultation events at the eastern side of the highest Andes Mountains during the initial mission months of COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate). This region is well-known for its high wave activity. We choose to study two pairs of GPS RO, both containing two occultations that occurred close in time and space. One pair shows significant differences between both temperature profiles. Numerical simulations with a mesoscale model were performed, in order to understand this discrepancy. It is attributed to the presence of a horizontal inhomogeneous structure caused by gravity waves.     

基于TCAD仿真建模的瞬时剂量率效应研究

针对一款百万门级0.18 μm互补金属氧化物半导体（0.18 μm CMOS）工艺抗辐射加固的微处理器电路,提出了采用TCAD仿真建模技术对加固电路开展瞬时剂量率效应研究的方法,仿真结果表明通过保护环结构加固设计,可有效提升电路的抗瞬时剂量率效应性能,并利用瞬时剂量率辐射源进行了仿真有效性的试验验证。结果表明,采用TCAD仿真手段得到的瞬时光电流峰值与试验得到的光电流峰值误差小于5%,证实了仿真研究电路瞬时剂量率效应方法的有效性。     

高温相变单元管蓄热过程数值模拟

对以高温共晶盐 Li F-Ca F2 为相变材料 (PCM)和以干空气为工质的相变蓄热系统 ,采用焓方法建立了以控制体单元为对象的单管相变蓄热模型。在模拟空间站太阳能吸热 /储热器轨道运行参数下进行了数值计算。计算结果与地面模拟试验数据进行了比较 ,吻合良好。     

塞式喷管底部二次流的数值模拟研究

从 N-S方程出发 ,采用二阶精度的 NND格式对塞式喷管的流场进行了数值模拟 ,重点研究了一线性塞式喷管底部二次流在低中高空的特性。研究表明 ,塞式喷管底部回流区的消失不仅与二次流流量大小有关 ,而且与底部压强有关 ;加入二次流会使塞式喷管的推力上升 ,但在大多数情况下其比冲会下降 ,只有特定压强比条件下 ,加入少量的二次流比冲才会上升     

环型超声速空气引射器零二次流流场数值研究

采用二维轴对称雷诺平均方程和标准κ-ε双方程湍流模型，数值研究了环型超声速引散器零二次流的流场结构及盲腔压强的变化，空间上采用二阶迎风格式进行耦合求解，时间上采用显示的Runge-Kutta方法进行迭代推进。结果表明，引射器几何参数不变的情况下，启动后的盲腔压强与引射气流总压之比为一常数；喷管马赫数不变情况下，喷管出口面积与混合室入口面积比越小，盲腔压强越低，扩压器性能越好，启动要求的总压越低，对超声速空气引射器的设计具有指导意义。     

高过载条件下绝热层烧蚀实验方法研究 (Ⅰ)方案论证及数值模拟

分析了高过载对固体火箭发动机流场和绝热层烧蚀的影响规律，提出一种新的研究思路：采用数值模拟方法来预示发动机三维两相流场，建立高过载流场模拟实验装置，开展绝热层烧蚀实验，建立高过载条件下的绝热层烧蚀模型，在此基础上发展高过载发动机绝热层设计和烧蚀预示方法。其中关键技术是高过载流场的模拟，对粒子加入法和弯管分离法两种方案进行了论证，认为弯管分离法原理上是可行的。为了验证这种方案的可行性，开展了弯管通道两相流的数值模拟研究，计算结果表明弯管装置具有使凝相粒子聚集形成高浓度粒子流的功能。     

涡轮效率改变对发动机加速特性的影响

采用零维闭环数值仿真平台，对某型单轴涡轮喷气发动机进行启动加速过程的零维闭环仿真，通过选择三种不同的调节方式，研究了涡轮效率的改变对发动机的转速、推力和耗油率等发动机特性的影响，其中某些结果与实验数据进行了比较。     

固体火箭燃气射流近场形成与发展的数值模拟

固体火箭武器燃气射流的近场区域存在有复杂的波系，膨胀波、压缩波的混合作用是机-弹、弹-舰相容性研究的重要内容，复杂波系压力、温度场的分布是燃气射流动力冲击和热冲击作用的直接因素。因为这一区域流动的复杂性，使得实验研究非常困难。为此应用数值分析的方法，研究了固体火箭高度欠膨胀燃气射流流场起始冲击波、近场波系的形成及发展。计算结果揭示了近场区域的一些特性，与文献提供的数据较为吻合，为工程应用提供了帮助。