Measurement of mass diffusion coefficients of O_2 in aviation fuel through digital holographic interferometry

The experimental apparatus to measure the mass diffusion coefficients of O2 in aviation fuel was constructed based on the digital holographic interferometry method. The theory of mass diffusion coefficient and interference image processing were introduced in detail. The accuracy of the experiment was verified by measuring the mass diffusion coefficient of 0.33 mol/L KCl in aqueous solution at 298.15 K. The mass diffusion coefficients of O_2 in RP3 and RP5 aviation fuels were measured at temperature from 278.15 K to 333.15 K, and the Arrhenius equation was employed to fit the experimental data. In terms of the Stokes-Einstein equation, the viscosities of these two aviation fuels were tested to estimate the correlation among mass diffusion coefficient, viscosity and temperature. A uniform polynomial calculation correlation was proposed to predict the mass diffusion coefficients of O_2 in both RP3 and RP5 aviation fuels, and its accuracy is considerably higher than that of the Stokes-Einstein equation.     

双合金热等静压复合工艺研究

主要探索采用双合金热等静压扩散连接工艺实现高温合金粉末和ＤＤ３单晶合金间可靠连接的可行性。研究内容包括热等静压（ＨＩＰ）扩散连接温度及热处理对ＦＧＨ９５—ＤＤ３复合界面的成分扩散、界面组织以及叶片材料本身组织性能的影响。研究表明，通过合理的工艺选择与改进，可以在保证对偶材料性能满足要求的前提下实现界面的良好扩散与结合。     

Reconnection Diffusion in Turbulent Fluids and Its Implications for Star Formation

Astrophysical fluids are turbulent a fact which changes the dynamics of many key processes, including magnetic reconnection. Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connections. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed “reconnection diffusion”. The astrophysical implications of this concept include heat transfer in plasmas, advection of heavy elements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that magnetic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection diffusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the process that is termed “ambipolar diffusion”. The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, ambipolar diffusion predicts that the coupling of mass and magnetic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view, i.e. appealing to the reconnection of flux tubes and to the diffusion of magnetic field lines. We make use of the Lazarian and Vishniac (Astrophys. J. 517:700, 1999) theory of magnetic reconnection and show that this theory is applicable to the partially ionized gas. We quantify the reconnection diffusion rate both for weak and strong MHD turbulence and address the problem of reconnection diffusion acting together with ambipolar diffusion. In addition, we provide a criterion for correctly representing the magnetic diffusivity in simulations of star formation. We discuss the intimate relation between the processes of reconnection diffusion, field wandering and turbulent mixing of a magnetized media and show that the role of the plasma effects is limited to “breaking up lines” on small scales and does not affect the rate of reconnection diffusion. We address the existing observational results and demonstrate how reconnection diffusion can explain the puzzles presented by observations, in particular, the observed higher magnetization of cloud cores in comparison with the magnetization of envelopes. We also outline a possible set of observational tests of the reconnection diffusion concept and discuss how the application of the new concept changes our understanding of star formation and its numerical modeling. Finally, we outline the differences of the process of reconnection diffusion and the process of accumulation of matter along magnetic field lines that is frequently invoked to explain the results of numerical simulations.     

稀土对硼铝共渗扩散机制的影响

建立了硼原子和铝原子的扩散模型 ,讨论了稀土对硼原子和铝原子扩散机制的影响。分析认为 :硼原子的扩散速度受 Fe2 B前沿硼原子向基体扩散速度的影响 ,也受硼原子通过 Fe2 B晶胞向基体扩散速度的控制 ;铝原子是在硼化物覆盖表面之前渗入的 ,当硼化物完全覆盖表面后 ,阻碍了铝原子的扩散 ,故铝在渗层次表面形成了化合物 ;稀土的渗入增加了空位数 ,使空位复合体的数量增加 ,也就加速了硼原子的扩散速度 ,增加了铝原子的渗入量     

钛合金/不锈钢网的扩散连接

探讨了钛合金／不钢网扩散连接的可行性,确定了直接扩散连接条件下的最佳工艺参数,分析了影响扩散连接的主要因素及接头微观形态。针对实际构件,深入分析了加压方式和变形率的关系,并提出了控制变形量得到无变形接头的方法。     

回流区中对涡与扩散火焰相互作用的数值模拟

对涡与扩散火焰的相互作用是涡轮喷气发动机燃烧室中十分重要的问题.本研究通过数值计算揭示了在对涡形成的流场中扩散火焰的结构以及扩散火焰对流场的影响.当不考虑释热引起密度变化时,数值解与相应的解析解符合较好.     

钛合金叠形波纹管的设计和制造

用有限元分析软件对叠形波纹管进行了结构设计,采用扩散连接方法和应力松弛技术制备了TA15钛合金叠形波纹管结构件.对高温扩散焊接叠形波纹管扩散连接界面微观组织、母材的晶粒度、材料的性能损失、气密性、刚度进行了分析和测试.结果表明采用扩散连接技术制备的叠形波纹管焊接接头良好,满足气密性、强度、刚度和疲劳性能要求.     

大厚度扩散焊NLU成像检测技术

针对钛合金大厚度扩散焊,基于非线性超声(Non-linear ultrasonic,NLU)原理,构建了一种NLU成像方法和检测系统,设计制备了不同的大厚度扩散焊试件,进行了NLU成像检测试验分析。检测结果表明,采用NLU成像检测方法,可实现钛合金大厚度扩散焊的超声可视化检测,最大检测厚度可达70mm。     

FGH95-K418B双合金热等静压复合工艺研究

采用热等静压扩散连接工艺实现了FGH95高温合金粉末和K418B铸造合金之间的可靠连接.研究了热等静压复合连接工艺对FGH95-K418B复合界面的成分扩散、界面组织的影响,以及对叶片材料组织和性能的影响.结果表明,通过合理的工艺选择与改进,可以在保证对偶材料性能满足要求的前提下实现界面的良好扩散与结合.     

来流条件对热流组分扩散项影响效应分析

使用数值模拟的方法研究了高超声速热化学非平衡流动中不同来流条件对热流组分扩散项的影响。以RAM-CII飞行试验外形为例,使用AUSM+-up格式耦合LU-SGS方法求解带化学反应源项的多组分NS方程。得到如下结论:在非平衡热环境数值模拟研究中,完全催化壁时组分扩散项热流所占比率表征了壁面催化效应的强弱;在同一高度下,随着马赫数升高热流组分扩散项比例越来越显著,而马赫数相同时,随着高度增高热流组分扩散项所占比例越来越小,主要原因在于当地化学反应进行程度不同。     

SPS温度对铜/镍粉/304不锈钢接头组织与剪切强度的影响

采用脉冲放电等离子烧结(SPS)制备了添加镍粉中间层的铜/304不锈钢接头,研究了焊接温度对接头组织及力学性能的影响。结果表明,以镍粉为中间层,可以实现铜与304不锈钢的扩散焊接。铜/镍界面处铜、镍互扩散形成铜/镍界面扩散层,镍/304不锈钢界面处镍、铁互扩散形成镍/铁界面扩散层,铜/镍扩散层厚度大于镍/铁扩散层厚度。在焊接压力为10 MPa、焊接温度为900℃时,铜/304不锈钢接头剪切强度最佳,为98 MPa。铜/304不锈钢接头断口形貌呈韧窝状,断裂均在镍中间层处,接头连接强度受制于镍中间层本身的强度。     

离心力场下扩散射流火焰的特性

以直段空腔和弯曲空腔为研究对象,在相同的初始条件下试验了两者之间火焰传播的特性,研究了强离心力条件下的扩散射流火焰特性.通过比较分析,在弯曲空腔中离心力场的影响下,扩散射流火焰受到浮升力的作用,以"焰泡迁移"的方式在主流中传播,加快了火焰传播速度,削弱了横向气流的干扰作用,使扩散射流火焰顺利地与空气掺混反应,增加了其在横向气流中的穿透深度.      

考虑气体扩散渗透的隔热材料瞬态隔热性能数值模拟

高超声速飞行器机动飞行时环境压力变化导致隔热材料沿厚度方向存在压力梯度,进而引起隔
热材料内气体的扩散渗透,影响隔热材料隔热性能。为研究气体扩散渗透对隔热材料隔热性能的影响,建立了
隔热材料内气体扩散渗透模型,采用罗斯兰德近似、有限体积法建立了隔热材料内扩散渗透及辐射导热传热计
算模型,对气体扩散渗透条件下的瞬态隔热性能进行了数值模拟。算例模拟结果表明:对2 cm 厚纳米隔热材
料,在外界气压为0. 1 MPa,绝热面为真空的状况下,当渗透率大于10-14 m2 时,气体扩散渗透开始影响隔热材
料内传热,导致隔热性能降低,气体黏性系数对气体扩散渗透有显著影响,随着黏性系数降低,气体扩散渗流现
象显著;衰减系数对绝热面温度响应有显著影响,随着衰减系数增大,绝热面温度响应显著降低。     

Determination of a soundproofing capacity of the model aircraft fuselage compartment

The results of experimental laboratory studies of an acoustic field inside the stiffened shell are presented; the shell simulates an aircraft fuselage compartment under its excitation by a diffusion sound field. The soundproofing capacity of the model compartment under diffusion excitation is experimentally evaluated.     

基于信息论匀质性测度的各向异性扩散相干斑抑制算法

 针对传统各向异性扩散抑斑算法存在的均匀区域噪声平滑不充分、边缘随迭代弱化及迭代次数的确定缺乏理论指导等问题,提出了一种新的各向异性扩散抑斑算法,该算法采用信息论匀质性测度作为图像中匀质区域与边缘的鉴别因子,使扩散系数能够更准确地控制扩散强度与扩散速率,从而达到充分平滑均匀区域噪声及保护边缘的目的。基于各向异性扩散方程求解与鲁棒误差范数最小化的等效性,提出了一种各向异性扩散方程的迭代停止准则。利用合成孔径雷达图像对本文算法的抑斑和边缘保持性能进行了仿真实验验证。结果表明,本文算法在均匀区域相干斑噪声抑制、边缘保持等方面均取得了优于传统算法的效果。     

波瓣喷管结构参数对引射混合器性能影响的数值研究

通过三维CFD数值计算,研究了波瓣喷管几何结构参数对波瓣喷管引射-混合器的影响规律。计算结果表明:瓣宽增加导致引射流量和波瓣出口处速度环量减小,热混合效率降低,但可以减小混合流动损失,提高总压恢复系数。波瓣扩张角的改变,对引射流量的改变因不同混合管尺寸而异,在混合管直径较小时,随着波瓣扩张角在20~°90°范围内增大,引射流量呈先增加后减小的趋势;在混合管直径较大时,引射量持续提高。扩张角的增加可提高速度环量,但是流动混合损失增加,总压恢复系数减小。      

TC4钛合金扩散焊接头的力学性能

在温度为910℃,压力为3.4MPa条件下对TC4钛合金板材进行了扩散焊接,对获得的扩散焊接头取样进行金相观察,仅在接近接头表面材料深度为1mm范围内发现未焊合缺陷,其余部分焊合较好,表明在给定工艺下可获得质量良好的焊接头.随后对TC4扩散焊接头的力学性能进行了试验研究,分别开展了静拉伸试验、断裂韧性试验及焊缝附近区域的纳米压痕试验.试验结果表明,所制得的TC4扩散焊接头屈服强度为887MPa,抗拉强度为948MPa,断裂韧性为101.9MPa·m1/2,均与原材料的性能相差不大.纳米压痕试验的结果显示,接头焊缝区和母材区的显微弹性模量分别为180.2GPa和178.0GPa.      

Ti3Al基合金及其与异种材料的连接研究现状

综述了耐高温轻质结构材料Ti3Al基合金及其与异种材料的连接研究现状，阐述了熔焊、钎焊、扩散焊、TLP扩散连接等主要连接方法的优缺点，指出了实用化研究方向。     

含Ni夹层SiCp/2014Al铝基复合材料扩散焊

利用中间添加Ni层,在610℃保温60min工艺成功实现了SiCp/2014Al铝基复合材料的真空扩散焊接.焊接之后利用金相显微镜(OP)、扫描电镜(SEM)、电子探针(EPMA)等对焊接接头进行分析.分析表明,Ni和Al之间相互扩散形成由金属间化合物构成的中间过渡层,主要由Ni3Al//NiAl//NiAl3组成.在理论上,计算出Ni和Al元素扩散浓度与焊接温度和保温时间之间的关系,以及元素的扩散距离与焊接参数之间的关系呈抛物线形变化.     

Cross Field Diffusion of Cosmic Rays in a Two-Dimensional Magnetic Field Turbulence

Cross field diffusion of energetic particles (cosmic rays) in a two-dimensional static magnetic field turbulence is studied performing test particle simulations. Qualitatively different diffusion processes are observed depending on the ratio of Larmor radius (ρ) to the correlation length (λ) of the magnetic field fluctuations. The diffusion is found to be composed of several regimes with distinct statistical properties, which can be characterized using Levy statistics. This revised version was published online in August 2006 with corrections to the Cover Date.