Numerical modeling of RadioAstron SRT temperature deformations

The results of modeling the thermal deformations of a space radio telescope’s reflecting surface are presented in the paper. Calculations were performed for the versions of the most unfavorable telescope illumination by the Sun.     

战术导弹固体发动机燃烧不稳定研究概述

介绍了大长径比战术导弹用固体发动机中产生的燃烧不稳定,分析了燃烧不稳定产生的机理,总结了国外典型的实验研究情况及其主要结论,以及国内固体发动机燃烧不稳定的状况。结合最新的研究进展,对燃烧不稳定的影响因素开展了深入分析:分析了声涡之间的耦合作用,重点讨论了声对涡的调制作用;分析了推进剂压强耦合对燃烧不稳定的影响,讨论了压强耦合响应函数的测试方法及其与推进剂配方之间的关系;分析了金属的分散燃烧及其凝相燃烧产物对燃烧不稳定的增益和阻尼作用。针对诸影响因素,提出了进一步的研究建议。     

Seepage flows instability in porous media

The goal of the present study is to investigate analytically, numerically and experimentally the instability of the displacement of viscous fluid by a less viscous one in two- and three-dimensional channels, and to determine characteristic size of entrapment zones. Experiments on miscible displacement of fluids in Hele–Shaw cells were conducted under microgravity conditions. Extensive direct numerical simulations allowed investigating the sensitivity of the displacement process to variation of values of the main governing parameters. The influence of three-dimensional effects (aspect ratio) on displacement instability was studied. One-dimensional model to simulate mixing flux due to frontal displacement instability was developed for engineering applications.     

Chemi-acoustic instability structure in irreversibly reacting systems

A basic understanding of the structure of the interactions between chemical and acoustic instabilities and the effects derived therefrom is sought for a medium undergoing one-step irreversible chemical reaction. Detailed examination of the acoustic-chemical system after the completion of the reaction shows the distinct presence of the chemical, acoustic, and mixed modes of instability. The chemical mode appears as a stationary yet spatially inhomogeneous entropy distribution, even though the medium initially (before reaction) is homogeneous throughout. The acoustic mode appears as a composite of both right- and left-travelling pressure or velocity waves, even though the initial acoustic wave is only right-travelling. The left-travelling wave is generated due to partial reflection or scattering as the right-travelling wave propagates in a spatially inhomogenous medium during the chemical reaction and is sustained even after the reaction is completed. The mixed modes of density and temperature fluctuations apparently retain to some degree the characteristics of both the acoustic and the chemical modes and may, under certain conditions, be dominated by either one of the modes of behavior. This is determined largely by the parameter Ω, the ratio of chemical to acoustic time scales.During reaction, it is found that the observed complicated behavior can be interpreted fruitfully in terms of the mode concept developed for the post-reaction behavior. It is observed that the temporal development of the physical fluctuating variables is dependent upon spatial position (the effect being stronger as Ω is reduced). Further, it is found that at specific values of Ω, the following effects are maximized: (a) acoustic amplification; (b) wave reflection; (c) reaction evolution enhancement.The energy contained in the fluctuations is found to be composed of an acoustic and a chemical part. The latter dominates during reaction. However, after reaction, the chemical part exactly balances any change in the acoustic part which occurs during reaction, thus resulting in no net change in the fluctuation energy. The chemical part seems to represent the loss (or gain) of mean thermal energy which was diverted by chemi-acoustic interactions into the increased (or decreased) acoustic energy of the system.     

粘弹塑性界面的断裂特性

研究张开型粘弹塑性界面断裂。用傅立叶正、余弦变换及逐段定积分变换方法将边值问题的控制方程化为奇异积分方程组。解方程后计算了裂纹尖端塑性区尺寸及裂纹尖端张开位移(COD：crack—tip opening displacement)，并给出了能量释放率算式。结果表明，裂纹尖端塑性区尺寸和COD均随两种材料的最小屈服极限的增加而减小；随时间的增大，COD先增长后衰减，最后渐近地逼近于定值。     

Shock tube study of boundary layer instability

An experimental study of the spatio-temporal evolution of the transition in a shock-tube wall boundary-layer has been carried out with thin film heat transfer gauges placed all along the tube. The results show that the transition appears, for small initial pressures, under the form of turbulent spots which are periodically created: these spots grow and are transported roughly at a velocity slightly smaller than the inviscid flow, regressing towards the contact surface. For higher initial pressures, a continuous transitional front is created which moves at about the same velocity as the shock-wave. These results seem to explain previous and often contradictory interpretations based on quasi-punctual measurements but the fact remains that the characterization criteria of the transition in unsteady boundary layers are still to be studied.     

螺栓连接结构接触面刚度识别方法

针对线性范围内的螺栓连接结构开展研究。在薄层单元理论基础上,提出了一种螺栓连接结构接触面刚度识别方法。采用正交各向异性本构关系的薄层单元模拟接触面,忽略螺栓和螺孔的影响,建立单个螺栓和多个螺栓搭接2种结构的初始有限元模型;根据试验模态参数,识别连接部位薄层单元材料参数。识别后,2种连接结构前四阶模态频率的计算结果最大误差不超过3.5%,表明识别后的薄层单元能准确反映接触界面的力学特征;文中方法适用于单个螺栓搭接和螺栓较密集工况的准确模拟。     

柔性接头界面端角点应力奇异性

基于界面理论,建立了柔性接头增强件、弹性件两种结合材料形成的界面端角点附近奇异应力场方程,依据界面连续条件和自由边界条件,得到了与奇异应力场关联的特征值λ的线性齐次方程组,通过该方程组的求解和公式推导,给出了柔性接头界面端角点附近含应力强度系数的奇异应力场和位移场;并根据特征值λ的取值范围,获得了应力奇异性消失的柔性接...     

涡轮泵转子失稳故障分析

轴套结构作为液体火箭发动机涡轮泵中典型结构,在其高速运转的过程中,存在着振动失稳的风险,因此需要分析轴套结构失稳的原因。建立了轴套结构内摩擦的动力学模型,推导了轴套结构内摩擦力的表达式,解释了带轴套结构的转子失稳机理,仿真得到了带轴套转子发生内摩擦失稳的振动特征,探讨了各影响因素对失稳门槛转速及失稳振动特性的影响规律,开展了实验验证,并给出了带轴套结构的转子稳定性设计建议。通过上述研究,发现转轴跨距、轴套半径、转轴刚度、偏心距和轴套与轴之间的间隙等因素是引发失稳的关键参数,需在设计与装配的过程中进行稳定性校核。获得的影响因素对失稳振动的影响规律,能够为具有类似结构的转子稳定性设计提供技术支撑。     

固体火箭发动机燃烧不稳定的影响因素分析和最新研究进展

总结和分析了国外对固体火箭发动机中出现的燃烧不稳定问题的理论、数值和实验研究.介绍了国外的研究思路和现状,详细阐述了固体火箭发动机中燃烧不稳定的主要影响因素,以及目前国外公认的不稳定触发机理--声/涡耦合、抑制措施及预测理论方面的进展,总结了有关发展大型分段式固体火箭发动机可能存在燃烧不稳定的相关信息,以期对国内固体火箭发动机在该方面的研究提供一定的参考.     

Numerical modelling of the interface conditions in coupled marangoni flows

The implementation in numerical codes of the coupling conditions between bulk phases adjacent to an interface exhibiting Marangoni effect is examined. The conditions are detailed in the case of a vorticity, stream-function, temperature formulation of the field equations. Numerical examples are reported for particular cases.     

NEPE推进剂粘接界面迁移组分定性分析

应用气相色谱-质谱(GC-MS),采用不同的色谱实验条件,用二氯甲烷萃取,对NEPE推进剂/衬层/绝热层ф25 mm圆柱标准粘接试件粘接界面不同沸点的迁移组分进行了定性分析研究。研究结果表明,推进剂中迁移组分主要有增塑剂硝化甘油(NG)、丁三醇三硝酸酯(BTTN)、稳定剂AD和燃速催化剂辛基二茂铁(ODCI),这些迁移组分可向衬层和绝热层迁移;衬层中迁移组分为增塑剂癸二酸二辛酯(DOS),该组分只向绝热层迁移,不向推进剂中迁移。     

高频燃烧不稳定性的试验研究方法及面临的挑战

采用特征时间法分析了液体火箭发动机燃烧子过程的响应特性,指出了高频燃烧不稳定性试验研究的重点。介绍了国内外典型的高频燃烧不稳定性模拟实验方法与试验装置,认为推力室声学、低压燃烧不稳定性模拟试验以及喷嘴动力学试验研究是目前指导工程设计的主要途径,高压燃烧过程试验和光学测量技术是未来充分认识其激励机理的关键。     

真空环境下高温气体静密封界面泄漏特性分析

文章基于气体热流润滑理论,建立高温气体静密封混合润滑分析模型,通过数值计算分析温度和表面粗糙度相关因素对静密封界面泄漏特性的影响。结果表明：考虑气体温黏效应和稀薄效应后,温度对气体静密封的泄漏率影响显著,温度从200 K升高到400 K时,泄漏率可降低20%以上;泄漏率亦受表面粗糙度大小、方向和分布形式的影响,其中粗糙度大小是主要因素,粗糙度越低泄漏率越小,表面粗糙度由0.8 μm减小到0.1 μm时,泄漏率可降低约3个数量级。可见,真空低泄漏静密封设计时气体热黏效应不可忽略;低泄漏率静密封表面的工程实现依赖于表面粗糙度的合理设计和工艺实现。     

预燃室低频不稳定燃烧仿真研究

为弄清燃烧不稳定性激励机制,建立了氢氧预燃室低频燃烧稳定性分析数学模型,利用MATLAB/SIMULINK集成软件包搭建仿真平台,研究了与供应系统耦合的低频不稳定燃烧。结果表明:在各种不稳定激励因素中,氧的喷注压降对稳定性影响最为显著,当其值低于某一稳定边界时,出现极限环振荡,提高氧的喷注压降可以非常有效地抑制低频不稳定燃烧;当氧的喷注压降位于稳定边界附近时,混合比将对稳定性产生一定影响,降低混合比可以较好地抑制低频不稳定;氢的喷注压降对低频燃烧稳定性影响很小。     

Boundary layer stripping of liquid drops fragmented by Taylor instability

A model is presented to describe the breakup of large ( 1 mm diameter) liquid drops by shock waves such as occurs in the heterogeneous detonation of liquid fuel sprays. After passage of a shock, high speed gas flow is established about the drops with large Reynolds number, large Weber number and large ratio of Weber number to the square root of the Reynolds number. Under these conditions, a thin liquid boundary layer is formed in the windward surface of a drop and is stripped from the drop at its equator. The rate of mass loss from the drop is small initially, but is increased an order of magnitude by fragmentation of the original drop. This fragmentation occurs because of Taylor instability of the windward surface of the accelerating drop. Calculations based on boundary layer stripping, which include the increase in liquid surface area due to fragmentation, give mass loss rates in general agreement with experimental observations.     

Nonlinear analysis of hydrodynamic instability in laminar flames—II. Numerical experiments

We consider a nonstationary nonlinear integrodifferential equation describing the evolution of a disturbed plane flame front. The following two-dimensional problems are solved numerically: (i) The formation of a wrinkled noncellular laminar flame front under conditions of spontaneous hydrodynamic instability. (ii) The formation of a turbulent cellular flame front under conditions of spontaneous diffusional-thermal instability. (iii) The formation of a turbulent wrinkled-cellular flame front under conditions of spontaneous hydrodynamic and diffusional-thermal instability. We compute the flame front velocity in laminar and turbulent propagation.     

Investigation of solid propellant combustion instability by means of a T-burner

Experimental investigation of solid propellant combustion instability using variable area T-burner is presented. The test facility is described and theoretical background and formulation related to the specific geometry are given. A number of solid propellants were tested over pressure oscillation frequency range of 350–1000 Hz. Results show complex behavior of the propellant response, and can characterize the different propellants according to their combustion instability level.     

面向空间应用的高可靠以太网接口设计

时间触发以太网;高带宽;降级传输;高可靠性