空间发动机系统关机过程水击现象理论分析

对空间发动机系统关机过程进行了数值仿真分析,讨论了关机过程中系统管路内的水击现象,以及多推力室发动机系统工作状态、阀门响应特性等因素对水击现象的影响。     

冲压发动机进气道压力振荡过程的数值研究

针对来流马赫数3.5,0°迎角飞行条件下冲压发动机的简化模型,数值模拟了进气道整流罩开启过程的非定常流动。计算采用AUSMPW有限体积格式,基于结构与非结构的混合网格技术,求解了非定常N-S方程。计算结果表明,在进气道整流罩打开以后,超声速气流会在燃烧室通道内形成振幅衰减较慢的低频剧烈振荡。在同样计算条件下采用Euler方程进行对比性研究,数值实验发现对这类大雷诺数、强非定常性的问题,Euler方程和N-S方程得到的结果相差不大。     

小偏差分析法在冲压发动机直连模拟试验中的应用

依据某给定几何尺寸亚燃冲压发动机的结构和性能参数,通过简化冲压发动机数学模型,理论推导了发动机直连试验模拟参数与推力之间的关系。针对其典型试验状态和工作特性,采用小偏差分析法计算了不同模拟参数及其组合对发动机推力和空气流量的影响结果。在此基础上,重点分析了不同模拟参数对发动机调节、高度和速度特性的影响规律,说明了模拟方法的合理性。该分析方法对固体冲压和液体冲压发动机地面直连试验性能评估具有一定指导意义。     

海流对出水空泡演化过程影响机理数值研究

采用数值仿真手段,重点针对海流对空泡演化过程的影响开展研究,形成考虑海流影响的空泡多相流理论与数值计算方法,分析了海流流向及流速影响,获得了海流对空泡发展演化的作用机制及对航行体流体动力特征的影响规律。研究结果表明:航向海流对溃灭阶段的空泡形态变化影响较为明显,不同海流工况下,泡内水、气分布有所不同,高压产生次序及溃灭过程的流动结构变化也因此不同。横向海流作用下的空泡形态差别不大,受到合成来流方向发生偏转的影响,迎流面向横向来流方向偏斜,造成空泡形状不对称。     

整体式液体冲压发动机导弹一体化设计

整体式冲压发动机导弹一体化设计,是把导弹与整体式液体冲压发动机作为一个系统,以系统性能最佳为目标,同时优选导弹和发动机的参数,文中以中程超音速飞航导弹为算例,针对整体式冲压发动机的特点,研究了导弹/整体式冲压发动机的一体化设计问题。对总体参数和发动机设计参数在中、低空巡航两种情况下进行优选,使导弹的射程达到了最佳,并分析、探讨了为适应不同巡航高度要求,选择导弹和发动机参数的有关问题。     

Development of a GNSS water vapour tomography system using algebraic reconstruction techniques

A GNSS water vapour tomography system developed to reconstruct spatially resolved humidity fields in the troposphere is described. The tomography system was designed to process the slant path delays of about 270 German GNSS stations in near real-time with a temporal resolution of 30 min, a horizontal resolution of 40 km and a vertical resolution of 500 m or better. After a short introduction to the GPS slant delay processing the framework of the GNSS tomography is described in detail. Different implementations of the iterative algebraic reconstruction techniques (ART) used to invert the linear inverse problem are discussed. It was found that the multiplicative techniques (MART) provide the best results with least processing time, i.e., a tomographic reconstruction of about 26,000 slant delays on a 8280 cell grid can be obtained in less than 10 min. Different iterative reconstruction techniques are compared with respect to their convergence behaviour and some numerical parameters. The inversion can be considerably stabilized by using additional non-GNSS observations and implementing various constraints. Different strategies for initialising the tomography and utilizing extra information are discussed. At last an example of a reconstructed field of the wet refractivity is presented and compared to the corresponding distribution of the integrated water vapour, an analysis of a numerical weather model (COSMO-DE) and some radiosonde profiles.     

GPS sensing of precipitable water vapour during the March 2010 Melbourne storm

The March 2010 Melbourne storm is used as a case study to examine the potential of using Global Positioning System (GPS) observations for studying the precipitable water vapour (PWV) field. The Victorian statewide GPS infrastructure network, i.e. GPSnet, was used in this study. GPSnet is currently the only statewide and densest GPS infrastructure network in Australia, which provides an excellent opportunity to examine the distribution of water vapour as the severe weather system passed over the state. Data from 15 GPSnet stations were processed over a one-week period, i.e. a few days prior to and after the storm passage, during which the course of the storm extended from the west to the southeast corner of the state. In addition, data from two radiosonde sites of the Australian Bureau of Meteorology Upper Air Network were used to compare and validate the GPS derived PWV measurements. The findings demonstrate that there is strong spatial and temporal correlation between variations of the ground-based GPS-PWV estimates and the passage of the storm over the state. This is encouraging as the ground-based GPS water vapour sensing technique can be considered as a supplemental meteorological sensor in studying severe weather events. The advantage of using ground-based GPS-PWV technique is that it is capable of providing continuous observation of the storm passage with high temporal resolution. The spatial resolution of the distribution of water vapour is dependent on the geographical location and density of the GPS stations.     

Report of the COSPAR mars special regions colloquium

In this paper we present the findings of a COSPAR Mars Special Regions Colloquium held in Rome in 2007. We review and discuss the definition of Mars Special Regions, the physical parameters used to define Mars Special Regions, and physical features on Mars that can be interpreted as Mars Special Regions. We conclude that any region experiencing temperatures > −25 °C for a few hours a year and a water activity > 0.5 can potentially allow the replication of terrestrial microorganisms. Physical features on Mars that can be interpreted as meeting these conditions constitute a Mars Special Region. Based on current knowledge of the martian environment and the conservative nature of planetary protection, the following features constitute Mars Special regions: Gullies and bright streaks associated with them, pasted-on terrain, deep subsurface, dark streaks only on a case-by-case basis, others to be determined. The parameter definition and the associated list of physical features should be re-evaluated on a regular basis.     

弱可压缩流体与可压缩流体模型的管路水击研究

为提升液体推进系统模型对可压缩流体的仿真能力,针对供应管路的瞬变流动,采用一维有限体积法,使用Modelica语言基于MWorks平台分别开发了适用于补燃循环发动机仿真模型库的弱可压缩流体与可压缩流体的管路模型,不同于控制方程中显含声速的弱可压缩流体模型,可压缩流体模型通过将守恒方程与真实流体的SRK型状态方程耦合求解来计算压力波的传播。在管路供应系统中,分别以液氢、液氧及液甲烷为工质进行关阀水击的仿真研究,结果表明:使用SRK状态方程避免了可压缩流体模型对内能拟合公式的依赖,减轻了建模难度;可压缩流体模型对液氧及液甲烷的仿真结果较为准确,最大误差不超过2%,对液氢的最大计算误差约9%;相对于可压缩流体模型,弱可压缩流体模型计算得到的水击压力在振幅及频率上均偏大;可压缩流体模型计算得到的流体密度波动不超过3%,因此工程实践中处理水击问题时将液体假设为弱可压具有一定的合理性。     

固体火箭冲压发动机含硼推进剂燃烧性能实验研究

利用地面直连试验系统对含硼推进剂在某固体火箭冲压发动燃烧过程性能进行试验研究。通过对含硼推进剂燃烧后凝聚相样品的SEM,EDS和XPS分析,探讨推进剂燃烧过程。在凝聚相EDS分析中,硼元素含量随着远离推进剂轴向方向显著降低,氧元素含量显著升高。在补燃室中,由于补充富氧空气,一次燃烧产物进一步反应,导致环境温度上升。由于高温,硼颗粒发生燃烧,产生大量气态硼化物,从而导致硼元素含量下降。二次燃烧凝聚相产物中,硼的非完全氧化物占比在40%以上,氮化硼占比在20%以上,硼颗粒占比7%以下。研究结果表明,随着推进剂在燃气发生器和补燃室内的一、二次燃烧,硼颗粒逐渐减少,并分别与环境中的C和O等元素发生化学反应,在凝聚相中的含量逐渐降低,氧元素在补燃室之后显著增加,氮化硼为凝聚相主要成分之一,存在于各特征位置。推进剂中的硼颗粒没有被完全燃烧,燃烧效率有待于进一步提高。