CH4/正癸烷混合燃料燃烧特性

为研究CH4/正癸烷混合燃料的燃烧特性及燃烧稳定性,在定容燃烧弹中测量了初始压力为0.1MPa、初始温度为420K、当量比范围为0.8~1.5和甲烷摩尔分数为0~0.8时CH4/正癸烷混合燃料的火焰扩散速度、拉伸火焰传播速度、马克斯坦长度、无拉伸火焰传播速度和层流燃烧速度等,分析了甲烷摩尔分数对马克斯坦长度及层流燃烧速度等的影响。结果表明:当量比为1.3时,随着甲烷摩尔分数的增加,火焰发展末期,前锋面由网格形胞状结构发展为光滑球面,火焰稳定性增强;甲烷摩尔分数增加导致混合燃料马克斯坦长度随当量比增加而减小的趋势变慢,实验研究范围存在临界当量比,当量比小于1.2时,甲烷摩尔分数为0.8的混合燃料燃烧稳定性较差,而当量比大于1.2时,甲烷摩尔分数为0.8的混合燃料燃烧稳定性较好;当量比在1.0~1.3范围内,甲烷摩尔分数为0.2和0.4的混合燃料层流燃烧速度较快,而在实验测量当量比范围,甲烷摩尔分数为0.8的混合燃料层流燃烧速度较慢。      

Numerical simulation of compression corner flows at Mach number 9

A hypersonic vehicle encounters a wide range of conditions during its complete flight regime. These flight conditions may vary from low to high Mach numbers with varying angles of attack. The near-wall viscous dissipation associated with flows at combined high Mach and Reynolds numbers leads to significant wall heat transfer rates and shear stresses. The shock wave/boundary-layer interaction results in a flow separation region, which commonly augments total pressure losses in the flow and lowers the efficiency of aerodynamic control surfaces such as fins installed on a vehicle. The standard turbulence models, when used to resolve such flows, result in incorrect separation bubble size for large separated flows. Therefore, it results in an inaccurate aerodynamic load, such as the wall pressures, skin friction distribution, and heat transfer rate. In previous studies, the application of the shock-unsteadiness correction to the standard two-equation k-ω turbulence model improved the separation bubble size leading to an accurate pressure prediction and shock definition with the assumption of constant Prandtl number. In the present work, the new shock-unsteadiness modification to the k-ω turbulence model is applied to the hypersonic compression corner flows. This new model with variable Prandtl number is based on the model parameter, which depends upon the local density ratio. The computed wall pressures, heat flux and flow field are compared to the experimental data. A parametric study is carried out by varying compression deflection angles, free stream Reynolds number and wall temperatures to compute the flow field and wall data accurately, particularly in the shock boundary layer interaction region. The new shock-unsteadiness modified k-ω model with variable Prandtl number shows an accurate prediction of initial pressure rise location, pressure distribution in the plateau region and heat flux in comparison to the standard k-ω model.     

燃烧室长度对固体燃料超燃冲压发动机燃烧室性能的影响

基于国外研究者完成的固体燃料超燃冲压发动机的实验数据,通过分别改变燃烧室等直段长度和扩张段长度,对不同总长的燃烧室工作过程进行数值模拟.采用基于压力的2阶迎风差分数值方法,物理模型为轴对称结构,燃烧模型采用有限速率/涡耗散模型(finite-rate/eddy-dissipation),湍流模型采用SST(shear stress transport) k-ω模型.聚甲基丙烯酸甲酯(PMMA)燃料进口边界由用户自定义函数的方式给定,分别分析了不同长度,即不同等直段长度或扩张段长度下超燃冲压发动机燃烧室内流场特性及其性能变化.结果表明:随着等直段长度的增大,燃烧室出口处燃烧效率逐渐减小,从72.74%降低至66.81%,而燃烧室内总压损失逐渐减小,燃烧室推力逐渐增大,可由85.83N增加至108.55N;改变扩张段长度,发现扩长段长度变化对燃烧室流场结构的影响较小,随着扩张段长度的增大,燃烧室出口燃烧效率和燃烧室推力都略微减小.在燃烧室长度的设计范围内,增大等直段的长度要比增大扩张段长度对提升燃烧室各项性能有帮助.      

煤体变形局部化的梯度塑性理论研究

摘 要 本文采用白光数字散斑相关方法对煤在单轴压缩下变形破坏进行研究，定量的测出了煤的变形局部化带宽度。并通过应变梯度塑性理论，在屈服函数中引入应变梯度二阶项。采用Drucker－Prager准则解析得出了煤试件的变形局部化带宽度公式并根据试验确定煤的材料内部长度。     

LEO卫星网络的切换策略及性能分析

采用Dijkstra算法,分析了低轨(LEO)卫星网络的距离最短、时延最小、跳数最小、持续时间最长等典型路由切换策略,并比较了性能。在综合考虑切换性能和时延等指标的基础上,提出了一种持续时间最长和时延最小组合,以及完全路由重构与部分路由重构结合的混合切换策略。各切换策略性能比较的结果表明,该混合切换策略的性能较优。     

GPS C／A码与P（Y）码抗干扰性能分析

讨论C/A码与P(Y)码重复周期的不同对各自抗干扰性能的影响。探讨涉及P(Y)码接收机抗干扰性能的认定问题。分析表明:多数情况下P(Y)码接收机具有比C/A码接收机远高出10dB的抗干扰性能;转发式干扰对P(Y)码接收机很难达到欺骗效果。     

管材探伤中最佳水声程问题的探讨

多年来，中小直径薄壁管超声水浸聚焦探伤法中，Ｈ＝Ｆ－√Ｒ＾２－Ｌ＾２被称为最佳水声程公式，但探伤实践中发现，实际最佳声程和由此式计算出来的理论最佳水声程出入较大，甚至完全不符。其原因是什么？此式存在的条件是什么？其适应性怎样？最佳水声程的涵义是什么？应如何确定？本文从理论和实践两方面对上述问题进行了分析，并提出了相应的结论。     

线搜索增强的率相关晶体塑性本构积分算法及数值实现

建立在晶体微观变形机制上的晶体塑性本构理论提供了研究细观尺度上晶体材料力学行为的理论与方法.在率相关晶体塑性本构积分方法中,Newton-Raphson(N-R)迭代方法往往是迭代求解剪切应变增量的核心算法.为了提高采用N-R迭代算法的晶体塑性本构积分方法的效率,在理论上采用线搜索方法对N-R迭代方法的迭代步长进行再规...     

环境条件对相机焦面影响的实验研究

环境条件,特别是温度和压力环境的变化,对相机焦面位置有很大影响,从而影响摄影照片的像质。文章用实验的方法定量地分析了温度和压力环境变化对相机焦面的影响。     

Spray characteristics of jet–swirl nozzles for thrust chamber injector

Thrust chamber injector is very critical component since that small differences in its design can result in dramatically different performance. This paper presents a preliminary investigation of a mono-propellant jet–swirl nozzle for thrust chamber using the existing commercial nozzle made of brass with little modification. The performance of two types of spray pattern, i.e. hollow cone and solid cone were investigated under cold flow test. Two solid cone injectors were studied at various purely axial orifice diameter with all other parameters remaining constant. This investigation reveals that decrease in the breakup length increased the spray angle. Higher injection pressure leads to shorter breakup length and higher value of discharge coefficient, except for hollow cone nozzle which shows mild fluctuating trend. Experimental data also tells that solid cone nozzle with diameter ratio 0.14 has the highest average discharge coefficient (0.60), followed by hollow cone nozzle (0.25). Solid cone nozzle with diameter ratio of 0.1 has an average discharge coefficient of 0.21.