X-ray, γ-ray and neutron detector development for future space instrumentation

An overview of the material developments currently being pursued by the European Space Agency (ESA) with respect to X-ray, γ-ray and neutron detection media is given. The benefits underlying the selection of specific materials are discussed. In the X-ray regime the basic microphysics behind degraded spectral performance caused by the polarization effect and Te inclusions, have been investigated. We have found that both effects degrade the spectra by producing a localised distortion of the electric field. The underlying cause for the distortion does however differ. For the γ-ray regime, a low-noise equivalent scintillator to LaBr₃ has been developed in the form of CeBr₃. Three inch crystals with a FWHM energy resolution of 4.4% at 662 keV have successfully been produced. For neutron detection, a boron compound based solid state neutron detector has been developed that is sensitive to neutrons, alpha particles and 60 keV X-rays. The measured detection efficiency in detection for thermal neutrons was found to be in the order of a few per cent.     

电弧推力器流场的数值计算

在流体计算软件fluent的微分方程中加入电磁项,可以计算电磁场作用下的流场。本文介绍了电弧推力器的理论模型,计算了电弧流场,并将计算结果和试验数据进行比较。分析了欧姆加热对提高工质气体比冲、降低推进剂消耗的作用,并根据流场温度分布,估计了电弧对电极的热烧蚀情况,提出了相应的解决方案。     

立式捏合机搅拌桨的设计

介绍了立式捏合机搅拌桨的设计方法和几何参数的计算方法;推导了两搅拌桨螺旋升角的关系式,根据捏合原理,建立了搅拌桨水平截面曲线的数学模型。     

Influence of thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations

Vortex-acoustic coupling is one of the most important potential sources of combustion instability in solid rocket motors (SRMs). Based on the Von Karman Institute for Fluid Dynamics (VKI) experimental motor, the influence of the thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations is numerically studied via the large eddy simulation (LES) method. The simulation results demonstrate that vortex shedding is a periodic process and its accurate frequency can be numerically obtained. Acoustic modes could be easily excited by vortex shedding. The vortex shedding frequency and second acoustic frequency dominate the pressure oscillation characteristics in the chamber. Thermal inhibitor position and gas temperature have little effect on vortex shedding frequency, but have great impact on pressure oscillation amplitude. Pressure amplitude is much higher when the thermal inhibitor locates at the acoustic velocity anti-nodes. The farther the thermal inhibitor is to the nozzle head, the more vortex energy would be dissipated by the turbulence. Therefore, the vortex shedding amplitude at the second acoustic velocity antinode near 3/4L (L is chamber length) is larger than those of others. Besides, the natural acoustic frequencies increase with the gas temperature. As the vortex shedding frequency departs from the natural acoustic frequency, the vortex-acoustic feedback loop is decoupled. Consequently, both the vortex shedding and acoustic amplitudes decrease rapidly.     

固体微推力器点火过程数值研究

为研究点火元器件加热区域受限下固体微推力器的局部点火过程,通过数值模拟手段,基于流固耦合传热模型和局部网格重构技术建立了推力器局部点火模型,研究了常压环境下的固体微推力器点火过程,分析了点火过程中推力器内燃气的流动和传热特性,并结合仿真所得推力-时间曲线与全表面点火模型和Jongkwang Lee提出的局部点火模型进行了对比。仿真结果表明,随着推进剂产生燃气往未燃推进剂表面的热反馈,推进剂燃面逐渐扩大。点火过程中喷喉燃气流速未达到声速,外界反压使微喷管内产生逆压梯度,导致喷管扩张段内出现边界层分离。由于喷管扩张段后部逆压梯度随时间增大,喷管扩张段后部回流相应加剧,从而增强了壁面表面的对流换热和燃气主流的动能耗散。模型的推力上升趋势与实际情况更加吻合。     

大型分段装药发动机绝热环烧蚀特性实验研究

为了研究大型分段装药发动机绝热环限燃层的烧蚀规律和特性,针对典型发动机开展了不同时刻和限燃层高度条件下三维两相流场的数值模拟,进行了限燃层表面烧蚀环境的特征分析和烧蚀状态参数提取,设计并研制了地面模拟烧蚀实验装置,开展了不同颗粒冲刷状态条件对限燃层烧蚀影响规律的实验研究,并采用扫描电镜分析了限燃层迎风面和背壁面炭化层的微观形貌。研究结果表明:(1)大型分段装药发动机流道中不同位置处绝热环限燃层表面的两相流冲刷状态不同,由于绝热环在流道中的阻碍作用,其表面形成了一种颗粒聚集浓度较低、冲刷速度较高而气相速度较低的烧蚀环境;(2)地面模拟实验结果表明绝热环限燃层的炭化烧蚀率随颗粒冲刷速度增加而增加,且增加幅度逐渐变大;(3)实验后限燃层的核心冲刷区域表面无炭化层残留,其烧蚀模式由机械剥蚀破坏效应主导。     

多异氰酸酯指标对推进剂力学性能的影响分析

为了确定推进剂中所用固化剂多异氰酸酯的质量指标，采用灰色关联度法分析多异氰酸酯的各项指标对推进剂力学性能的影响，通过计算发现：（1）影响多异氰酸酯粘度的主要因素是高官能度的含量，而二官能度的含量是影响其平均官皮肤度的主要因素；（2）二官能度的含量是影响推进强度的最重要因素，而三官能度的含量和粘度是影响其伸长率的最重要因素。对于不能建立明确回归模型的实验，灰色关联度法可用于原材料多因素实验中的影响因素主次分析。     

复合丁羟推进剂压强指数现状评述

本文详细叙述了我国研究压强指数的历史、低压强指数的优点,列举了我国丁羟推进剂压强指数研究的状况,分析比较了国内外水平,指出了今后努力方向.     

固体火箭复合结构喷管传热的隐式计算方法

采用适用于多层复合结构的当量热容瞬态热传导方程,通过坐标变换解决多个移动边界问题,用ADI方法推导了二维隐式求解格式,在与烧蚀相耦合的情况下获得了复合结构喷管的温度分布。用隐式方法计算有效地减少了计算机时,对工程设计大有裨益。     

粒子侵蚀的相似规律及实验模拟问题

本文探讨了粒子侵蚀的相似规律,给出了粒子侵蚀实验的模拟参数,讨论了相似规律在实验模拟中的应用及实验模拟问题。