基于MHD的磁射流抛光中流场的分析与模拟

从理论上分析了磁射流抛光中的磁场与流场的相互作用,构建了磁射流抛光的冲击射流模型,基于磁流体动力学对磁射流抛光过程的紊动冲击射流进行数值模拟,得到了磁射流抛光过程的连续流场和射流在工件壁面上的压力、速度、紊动强度分布。通过比较射流抛光和磁射流抛光的数值计算结果,分析了磁流变效应对射流稳定性的影响,从射流的流场、速度、紊动强度等方面分析射流在磁场中稳定的原因。     

射流抛光多相紊流流场的数值模拟

 理论分析了射流抛光的紊动冲击射流特点,构建了射流抛光的垂直冲击射流模型和斜冲击射流模型。根据射流抛光冲击射流的特点,比较各种流体模型后,采用RNG k-e 模型应用于射流抛光模型的计算。利用计算流体力学理论的二阶迎风格式对抛光模型方程离散,用SIMPLEC数值计算方法对射流抛光过程的紊动冲击射流和离散相磨粒分布进行数值模拟,得到了射流抛光过程的连续流场和离散相磨粒与水溶液的耦合流场,同时计算出了抛光液射流在工件壁面上的压力、速度、紊动强度、剪切力分布和磨粒体积质量分布,分析了垂直射流抛光模型和斜冲击射流抛光模型紊流流场的特点。     

轴向脉冲电流对射流线性不稳定性的作用

为了提高电磁被动装甲对聚能射流的防护能力,利用叠加原理和磁流体线性不稳定理论,在轴向脉冲电流作用下建立了射流运动线性扰动控制方程,并对射流箍缩和扭曲不稳定性增长率随粘性、时间的变化规律进行了分析,得到了射流不稳定增长率和射流的变形规律,并利用数值方法得到了射流变形的计算公式。最后通过直径39.2mm破甲弹进行静破甲试验,通过后效板射流入射孔的大小验证了脉冲电流对射流的箍缩作用;利用具有初始弯曲、直径为1.75mm铜丝模拟了脉冲电流对射流的扭曲作用,通过铜丝的变形验证了脉冲电流对射流的扭曲作用。实验结果证实了理论分析的正确性。     

自由表面磁流体射流不稳定性分析(Ⅱ)

用微分解析方法分析了自由表面磁流体射流在两个非均匀、相互垂直的横向磁场中的稳定性行为。获得了在给定射流初始速度分布和磁场分布条件下射流的速度空间分布表达式;分析了射流扭转及向外溅射的位置。     

水下射流流场分析与试验

光学窗口长期处于水下环境中容易滋生水生物,水生物的附着影响光学窗口的观察与使用。为抑制或去除附着水生物,采用水下高速射流的方法。水下射流不同于空气中射流,由于环境水的作用会有很大的能量消耗,而目标前射流的流场对清洗效果具有十分重要的影响,故而进行水下射流流场分析和试验研究。通过水下射流流场分析,获得目标前的流场参数。根据流场分析结果,设计了水下射流装置。水下射流装置由潜水电机、泵、喷管和控制箱组成。运用试验装置进行了水下射流试验,取得了喷口前300 mm处2.2 m/s的流速。运用水下射流装置定期对处于水下环境的光学窗口进行水下射流可以去除初期附着的水生物和污垢,也可以抑制水生物生长,保持光学窗口的洁净。     

自由表面磁流体射流不稳定性分析(II)

用微分解析方法分析了自由表面磁流体射流在两个非均匀、相互垂直的横向磁场中的稳定性行为。获得了在给定射流初始速度分布和磁场分布条件下射流的速度空间分布表达式;分析了射流扭转及向外溅射的位置。     

基于CFD的射流抛光喷射距离的分析和优化

分析了喷射距离对射流抛光效果的影响,基于计算流体动力学进行了喷射距离的分析和优化.通过构建射流抛光不同喷射距离的物理模型,采用能更好地处理流线弯曲程度较大的流动的RNG k-ε紊流模型应用于射流抛光的数学建模,使用SIMPLEC算法对射流模型进行数值计算,得到了不同模型的射流抛光冲击射流流场及工件壁面上的冲击压力、紊动强度、壁流速度分布.根据射流抛光对冲击射流特性的要求,比较和分析不同喷距模型的数值仿真结果,结果显示,射流抛光最优化喷距范围为喷嘴口径的10倍至12倍之间.     

杆式射流侵彻半无限靶的理论分析

 理论分析高速杆式射流侵彻半无限靶过程时,考虑速度梯度对聚能射流的影响,将射流进行分段计算,得到了射流拉伸后实际碰靶时的微元长度和直径变化。采用伯努利方程和静力学方法,通过对射流形状和速度分布作线性近似,理论分析了高速杆式射流侵彻半无限靶的过程,得到了靶体中的侵彻深度和侵彻孔径与射流长度、速度及直径之间的关系。将模拟结果与实验结果进行对比,结果表明理论分析结果与侵彻实验结果符合较好。     

射流冲击模型在水下爆炸实验中的应用研究

 为研究射流冲击载荷对结构的作用效果,从理论和数值角度研究了射流的载荷特性,以舱段模型实验为研究对象,建立了射流计算模型,结合实验数据,对射流冲击问题进行了分析。结果表明,射流冲击能够造成结构强烈的局部响应,某些情况下,射流冲击载荷引起的结构响应甚至比冲击波载荷引起的响应更大。因此,中近场水下爆炸实验需要考虑射流的影响。建立的射流模型能够较好地反映射流冲击的载荷特性,为水下爆炸实验分析提供了一种新的手段。     

浮力对矩形射流扩散火焰影响的大涡模拟

本文对浮力作用下的矩形射流扩散燃烧过程进行了三维大涡模拟。数值模拟结果展示了浮力作用下矩形射流扩散火焰的动态弯曲过程,比较分析了射流速度对火焰刚性的影响,发现射流速度越高火焰弯曲程度越小、燃料喷射距离越远。对浮力作用下的水平射流横截面流动分析结果表明,由于流向涡的卷吸作用在局部区域存在逆着浮力方向的流动。     

Sufficient conditions for linear long-wave instability of steady-state axisymmetric flows of an ideal liquid with a free boundary in an azimuthal magnetic field

The problem of linear stability of steady-state axisymmetric shear jet flows of an inviscid ideally conducting incompressible liquid with a free surface and “frozen-in” azimuthal magnetic field is analyzed. The sufficient conditions for theoretical (on semi-infinite time intervals) and practical (on finite time intervals) instability of these flows relative to small axisymmetric long-wave perturbations are obtained by the direct Lyapunov method. An a priori lower estimate indicating (at least) an exponential increase with time of small perturbations under investigation is constructed in the case when these conditions are valid for theoretical as well as practical instability. In addition, an illustrative analytic example of steady-state flows under investigation and small axisymmetric long-wave perturbations superimposed on them is constructed (according to our estimate, these perturbations increase with time).     

方管锂铅磁流体氚增殖剂中的氚输运模拟

利用COMSOL Multiphysics软件实现磁场、导电流体、氚输运的多物理场耦合,研究了在强磁场下3维方管中锂铅流体内的氚输运及其分布。通过计算得到,锂铅流体在平行磁场方向的导电壁侧形成了射流,而在哈德曼壁侧及流体的芯部区域流动滞缓;射流的强对流效应使得在导电壁侧具有较低的氚浓度,而在哈德曼壁面侧及流体芯部具有较高的氚浓度累积,形成了不对称的氚浓度体分布。     

几种液体金属自由表面的MHD不稳定性实验研究

介绍了在核工业西南物理研究院的液态金属实验回路(LMEL)上获得的几种可供液态偏滤器-限制器系统选用的液体自由表面的磁流体动力学(MHD)效应不稳定性的实验结果。实验发现：自由表面射流在穿越梯度横磁场时射程变短、截面变扁平,但MHD效应稳定,调节射流与磁场的夹角可以控制射流的流动特性;自由表面膜流MHD效应存在三种现象,即层流、溪状流和湍流。层流是由多束射流打到固体表面产生的(简称“射-膜流”),从MHD效应角度考虑,“射-膜流”将是四种可选液态偏滤器-限制器系统的液体自由表面形式中最佳的选择。同时,探讨了从物理的角度来理解四种自由表面形式的MHD效应的现象。     

Effect of Acoustic Field on the Structure of a Round Minijet

Presented are results of visual studying the structure of a round minijet flowing into the atmosphere exposed to an acoustic field. The studies were performed with the laminar jet flow. According to the photo and video recording of the flow pattern we revealed characteristic features of the jet structure in the acoustic field. Characteristic vortex structures and zones with intensive turbulent mixing were detected in the flow.We revealed the process of formation of vortex structures in a laminar jet under the action of the acoustic field, vibrational and rotational jet flows at the outlet of the pipe 1.35 mm in diameter. The present study is a continuation of the research on a minijet structure in an acoustic field [13].     

Behavior of underexpanded plasma jet in strong magnetic field

A visual study of underexpanded plasma jet was conducted to reveal the detailed behavior in the strong magnetic field. The images of the jet were taken by a digital single-lens reflex camera through viewing windows. The distribution of optical intensity obtained from the raw data was compared to that of the typical emission line intensity. The profile of the optical intensity agrees well with that of the emission intensity. It is illustrated that the typical structure of underexpanded jet such as Mach disk is also affected obviously by the magnetic field. The radial distribution of number density was determined by using the image analysis based on the Abel-inversion. The converted data clarify the jet behavior that is hidden on the ordinary observation. The density obtained from numerical analysis for a simple gas was also compared with the number density. It is confirmed from the comparison with numerical results that the radial profile of number density can be utilized for understanding the plasma jet behavior under the strong magnetic field.     

Cathode jets and the retrograde motion of arcs in magnetic fields

The influence of a transverse magnetic field on the jets of an impulse discharge was investigated. It was found that the jet trajectories show a curvature. The amount of the curvature depends on the pressure, the magnetic field intensity, the discharge current, the material and the polarity of the electrodes. The curvature of the jets was explained as a result of the action of forces arising in a plasma flow through a magnetic and electric field; their analysis was carried out on the bases of a MHD model. On hand of a derived solution, a possible influence of the jets on the origin of a retrograde motion is discussed. It is shown that the existence of certain discharge parameters and of a certain magnitude of the magnetic field brings about, in a plasma flying through a magnetic field, an induction of fields and currents under the action of which, on the one hand, the plasma itself flows in a retrograde direction and, on the other hand, there are influenced the trajectories of the carriers (particularly those of ions) of the current in the channel of discharge in front of the cathode spot. The proposed model of the retrograde motion is discussed and compared to the known results.     

非均匀磁场中等离子体射流质量色散强度

研究了非均匀磁场中多质量射流的运动轨迹,推导出质量色散强度表达式。考虑到不同入射方式及羽流角度的情况下,应用MATLAB模拟射流的运动轨迹,计算出质量色散强度,并同均匀磁场中的质量色散强度大小相比较,以确定该种磁场中射流质量分离的效果。模拟结果表明:非均匀磁场中多质量射流的质量色散强度大于均匀磁场的情况,可实现等离子体射流的高效质量分离。     

Voltage of the vacuum arc with a ring anode in an axial magneticfield

The plasma jet focusing and voltage distribution in the interelectrode gap of a vacuum arc with a ring anode and subjected to an axial magnetic field were studied theoretically. A two-dimensional model was developed based on the free plasma jet expansion into vacuum, and the steady-state solution of the fully ionized plasma in the hydrodynamic approximation was analyzed. It was found that the imposition of an axial magnetic field reduces the radial expansion of the plasma jet. The characteristic jet angle decreases from about 40° in the zero magnetic field case and approaches a value of about 20° with a 0.02 T magnetic field. The arc voltage consisting of the cathode drop, the plasma voltage drop, and anode sheath drop increased, with the imposition of a magnetic field, and decreased with the anode length. The model was compared to experimental measurements of the vacuum arc voltage behavior in an axial magnetic field, and good agreement was found     

激光驱动磁重联过程中的喷流演化和电子能谱测量

利用神光Ⅱ激光器和日本大阪大学Gekko激光器构建了激光驱动等离子体磁重联过程. 在垂直于磁重联平面方向发现了高速喷流, 从不同观测方向实验证实了该喷流的存在并测量了喷流的流体力学演化过程, 对其中的电子能谱进行了诊断分析.     

Generation of magnetic field during shearing motion of a conducting viscous medium

Magnetic field generation in shear flows of an incompressible viscous conducting medium across the flux lines of the initial field created in them is considered in the framework of the plane 1D problem of magnetohydrodynamics. The conditions of free slip and “sticking” are stipulated at the boundary between the flows. The variations of the magnetic field and velocity of shear flow occurring in the moving medium correspond to an Alfven wave “spreading” during its propagation due to dissipative processes in the medium associated with its viscosity and electrical resistance. It is shown that a high-rate shear of metals under explosive or impact loading may lead to generation of megagauss magnetic fields.