Nonequilibrium Ionization Behind a Strong Shock Wave in the Mars Atmosphere

The paper reports results of experimental and numerical studies of nonequilibrium ionization behind a strong shock wave in the Mars atmosphere. The calculated kinetic model is verified by measuring the electron concentrations and temperature in the relaxation zone     

Interference of a Bow Shock with an Oblique Shock and an Isentropic Compression Wave

The features of the flow in the zone of interaction between a plane bow shock and an oblique shock or an isentropic compression wave are studied. The limiting interaction regimes are considered analytically, the similarity conditions are formulated, and the limiting values of the flow parameters are determined for the high-pressure compressed gas jet formed in the interference and for the body surface. On the basis of a numerical solution of the Euler equations the flow specifics in the neighborhood of the spreading line on the body are determined and ways of reducing the dynamic and thermal loadings on this line are proposed.     

燃气射流起始冲击波场形态的实验研究

介绍利用激光摩尔偏折仪和压阻式压力传感器对发动机喷流起始冲击波的基本形态进行的研究． 研究结果验证了在燃气流团前存在着起始冲击波及发展初期具有非球面的特性,并提出了喷口起始冲击波波阵面发展的新结构,对前人有关起始冲击波发展结构的研究结果进行了修正．     

Numerical Investigation of the Temperature Macroparameters in a Shock Wave in a Binary Gas Mixture Using the Kinetic Boltzmann Equation

The effect of the Mach number and the concentration and mass ratios on the behavior of the parallel, radial, and total temperatures of the components in a shock wave in a binary gas mixture is studied. The results obtained are compared with the theoretical and experimental results of other investigators.     

Computational and Experimental Investigation of the Development of Turbulent Mixing in a Gas Layering in Passage of a Shock Wave

The experimental data and the results of direct numerical simulation of the flow developed in a constant-cross-section tube in passage of a shock wave through a three-layer gas system are presented. The three-layer systemis formed as a result ofmounting two thin films in the tube and filling the space between them with gases of different densities. The first interface (thin film) makes an angle of 45? with the shock front and the second interface is located in parallel to the front. The shock wave is formed at the left tube end and moves towards the first interface at the Mach number M = 2.4. The results of simulation of the problem are compared with the experimental data.     

Numerical Study of a Turbulent Flow Compressed by a Weak Shock Wave

Abstract

Modification of a two-dimensional isotropic trbulent flow by passage of a weak shock wave was numerically studied by the explicit spectral collocation method with the fourier series in the ranges of M₁ = 0.14?0.21 and M_s = 1.06?1.14. The density 1 trbulent kinetic energy increased by 10 to 19 % and density fluctuation increased by 14 to 50 % in proportion to the shock wave mach number. The amplification of turbulent kinetic energy did not change by increase of the turbulent Mach number, while that of density fluctuation decreased from1.35 to 1.15%. The argumentation of turbulent kinetic energy appeared at moderate and high wave numbers of energy spectra and resulted in a reduction of the integral scale by3.33 to 5.4%. Modifications mechanisms of turbulent kinetic energy, density fluctuation and vorticity were verified by the transport equations It was shown that the decreased amplification of the density fluctuation In the increased trbulent Mach number attributed to the unchanged production terms and the negative dilatation correlation behind the shock wave.the vorticity-dilatation term was responsible for more than 80 % of the total vorticity production at the shock front.     

流动肥皂膜气体界面及其在柱状汇聚激波作用下演化的实验研究

在Richtmyer-Meshkov(RM)不稳定性实验研究中,形成两种不同密度流体的初始扰动界面是前提和关健.本文提出了一种流动肥皂膜气体界面生成方法,其工作原理是由细丝构成的导流框从激波管实验段穿过,肥皂液从导流框的上端注入并在重力作用下在导流框中形成流动肥皂膜,膜的两测可以分别充入不同密度的气体从而形成稳定的气体...     

Controlling the Parameters of a Shock Wave by Means of the Mass and Energy Supply

The process of controlling the parameters of a bow shock created by a body flying at supersonic velocity by supplying mass and thermal energy behind the shock is investigated. The mass and thermal energy were supplied by means of fan air jets flowing out from the body and hydrogen combustion in the neighborhood of the model, respectively. The flow parameters were measured in the neighborhood of the model and recalculated for greater distances. For these control methods some features of the variation of the shock intensity and momentum are presented. A generalization of the effect of the thrust of the nozzles forming the jets and their orientation on the shock wave parameters is obtained. The control methods considered are compared with each other.     

磁场对电磁弹性板中Lamb波频散特性的影响

研究了静态磁场下电磁弹性结构中Lamb波的传播行为.在确定静态磁场下电磁弹性板中耦合初始广义应力(弹性应力、电位移和磁感应强度的基础上,推导了含初始广义应力时板中Lamb波传播的运动方程,并由此获得了对称模态和反对称模态时的频散方程.以由BaTiO3-CoFe2O4材料构成的电磁弹性板模型作为数值算例,绘制了Lamb波传播的对称模态和反对称模态频散曲线.计算结果表明磁场对Lamb波的频散特性有一定的影响.     

Wave Processes in the Hypersonic Shock Layer on a Flat Plate

An electron-beam fluorescence technique is used to investigate the properties of density waves in the shock layer on a flat plate placed in a hypersonic stream (M_x=21) at zero incidence; the Reynolds number based on the longitudinal coordinate and the freestream parameters is Re_x=(2.7–3)·10⁵. Transverse profiles of the mean density and the overall and spectral levels of the density fluctuations are obtained, the longitudinal and lateral phase velocities of the waves and the correlation scales are determined, and the longitudinal increments of the waves are derived. The data are compared with the experimental results obtained at Re_x=(2.6–7)10·⁴.     

On the Mutual Penetrations of Two Fluids Whose Interface is Accelerated by a Shock Wave

A shock tube experimental investigation and numerical simulations are undertaken to study the evolution of a perturbed interface of two different gases accelerated by a shock wave. The experimental method is based on a high-speed camera laser sheet diagnostic technique, and simulations are provided by our code CARBUR based on a finite volume discretization of Navier–Stokes’s equations. Two gas pairs are used to illustrate both the heavy/light (air/He) and the light/ heavy (air/SF₆) cases. Two simultaneous large initial perturbations, one positive and one negative, are tested for an incident shock wave Mach number in air of about 1.3. The thin membrane (less than 1 μ) which materializes the initial interface between the two test gases presents 2D perturbations whose wave number is close to 1 in order to rapidly reach the non-linear regime. The development of the perturbations is captured at a frequency of 10 kHz after the interface acceleration, and the experiments are complemented with a numerical simulation to validate the interface deformations. Results show an asymmetric mutual gas penetration increasing with the absolute value of the Atwood’s number. Furthermore, they confirm that the heavier gas penetrates the lighter as thin spikes and the lighter gas penetrates the heavier as large bubbles. Moreover, we show that the spike moves faster than the bubble in the heavy/light case and slightly faster in the light/heavy one. Finally, numerical and experimental results are in agreement.     

Investigation of the Nitrogen Shock Wave Structure on the Basis of Trajectory Calculations of the Molecular Interaction

The shock wave structure in a diatomic gas is investigated using the direct statistical simulation (Monte-Carlo) method. The energy exchange between translational and rotational degrees of freedom (TR-exchange) is calculated by solving the dynamic problem of the interaction between rigid-rotator molecules within the framework of classical mechanics. The density profiles calculated are compared with the experimental data and on this basis the nitrogen rotational relaxation time is estimated. The possibility of using simplified intermolecular interaction models, namely, the variable-diameter sphere model employed together with a phenomenological consideration of the TR-exchange, is studied. Gasdynamic parameter profiles in the shock wave are analyzed. Simple approximations of the velocity gradient and translational and rotational temperature profiles are obtained on the basis of a parametric calculation of the shock wave structure. This makes it possible approximately to describe the gasdynamic parameter profiles in terms of elementary functions.     

Collective Bow Shock Ahead of a Transverse System of Spheres in a Supersonic Flow Behind a Moving Shock Wave

The results of investigating the dynamics and physical conditions of formation of a collective bow shock ahead of a system of spheres with the line of centers normal to the supersonic flow behind a traveling shock wave are presented. Two types of shock-wave patterns that necessarily precede the formation of the collective shock wave and correspond to regular and Mach interaction of the bow shocks were detected experimentally. On the basis of a local gasdynamic-discontinuity interference theory, quantitative criteria of the existence of these regimes and of the formation of a common shock wave are determined. These criteria are confirmed in a series of experiments for the transitional regimes.     

On the Passage of a Shock Wave through a Layer of Charged Gas

A class of exact solutions of the ideal electrohydrodynamics equations is presented. These solutions describe the propagation of a plane shock wave along a static background with decreasing density in the presence of gravity and longitudinal electric fields. This class of solutions contains an arbitrary function of the Lagrangian variable which makes it possible to consider many physically different cases.     

岩石对冲击波的非线性动态响应

对干燥、饱水、饱泵油大理岩和饱和砂岩进行了SHPB冲击压缩实验,得到了干燥岩石和饱和岩石的应力波衰减规律。在应力波传播过程中,其幅值有较大的衰减,干燥岩石的衰减最大,且孔隙度越大衰减越大,饱和岩石还存在较强的波弥散效应。在小于岩石屈服强度时,多次冲击加载下获得随冲击加载次数的增加,加载模量增大,残余应变减小的压实效应。这一结果可用于大型地震工程和防护工程的设计和建造。     

On the Normal Reflection of a Shock Wave from the End of a Rectangular Cavity

The normal reflection of a plane shock, propagating in carbon dioxide at the Mach number 3.7, from the end of a cavity with a rectangular cross-section is experimentally investigated in a shock tube. The flow is visualized using the Cranz-Schardin system. Streak photographs and shadowgraphs of the time-dependent interaction of the reflected shock with the boundary layer under separation conditions with three-shock system formation are presented. On the basis of the experimental results the process of time variation of the flow pattern is described, the triple point trajectories are determined, and their distinctive features for the case of coalescence of the bifurcation zones, formed at opposite sides of the cavity, are discussed.     

On the Electric Potential Induced by a Homogeneous Magnetic Field in a Turbulent Pipe Flow

In this paper we study a turbulent pipe flow of a weakly electrical conducting fluid subjected to a homogeneous magnetic field which is applied perpendicular to the flow. This configuration forms the basis of a so-called electromagnetic induction flow meter. When the Hartmann number is small so that modification of flow by the Lorenz force can be neglected, the influence of the magnetic field results only in a spatially and temporally varying electric potential. The magnitude of the potential difference across the pipe is then proportional to the flow rate and this constitutes the principle of the flow meter. In this study the flow and electric potential are computed with help of a numerical flow simulation called Large-Eddy Simulation (LES) to which we have added an equation for the electrical potential. The results of the LES have been compared with experiments in which the electric potential is measured as a function of time at several positions on the circumference of the pipe. Both the experimental and numerical results for the mean potential at the pipe wall agree very well with an exact solution that can be obtained in this particular case of a homogeneous magnetic field. Furthermore, it is found that fluctuations in the electric potential due to the turbulence, are small compared to the velocity fluctuations. Based on the results we conclude that electrical-magnetic effects in pipe flow can be accurately computed with LES.     

Evolution of Controlled Disturbances in the Shock Layer on the Compression Surface

Results of an experimental study of density-wave characteristics in the shock layer are presented for the case of a hypersonic nitrogen flow around a model with a two-dimensional compression surface, which is an arc of a circle, and a sharp leading edge. Controlled periodic disturbances developed on the streaky structure are registered by the electron-beam fluorescence technique. The streaky structure of the type of two vortices rotating in the opposite directions is generated in the shock layer by an oblique gas-dynamic whistle.     

偏置磁场对磁致伸缩纵向导波换能器效能的影响研究

为提高磁致伸缩导波换能器的激励效能,本文研究了磁场结构参数对偏置磁场空间分布的影响。基于COMSOL有限元仿真平台,对磁致伸缩换能器磁场分布特性进行了数值计算,研究了磁路结构形式、磁路和永磁铁数量等对偏置磁场分布的影响,最后优化出适合纵向导波激励的磁场结构参数。检测实验结果表明,随着偏置磁场磁路数量的增加,偏置磁场强度增大,磁场径向均匀性更好,磁致伸缩换能器的效能也相应提高;在相同磁路数量的条件下,永磁体数量的改变对换能器效能影响较小,四磁路偏置磁场最优;轭铁中部增加永磁铁后的磁路结构的偏置磁场的轴向均匀性更高,其激励效能更好。     

激波在平板上诱导的旋涡强度的测量

运动激波通过两个等攻角平板后诱导出两个同向旋转的旋涡，这两个旋涡在随当地气流向下游运动的同时，绕涡核连线中心旋转。本文通过测量涡对的转动角度速度，获得了每个旋涡的强度。实验结果表明，由此测得的旋涡强度不同用于小攻角平板起动涡公式计算了起动涡强度。