An asymptotic preserving scheme on staggered grids for the barotropic Euler system in low Mach regimes

We present a new scheme for the simulation of the barotropic Euler equation in low Mach regimes. The method uses two main ingredients. First, the system is treated with a suitable time splitting strategy, directly inspired from the previous study that separates low and fast waves. Second, we adapt a numerical scheme where the discrete densities and velocities are stored on staggered grids, in the spirit of MAC methods, and with numerical fluxes derived from the kinetic approach. We bring out the main properties of the scheme in terms of consistency, stability, and asymptotic behavior, and we present a series of numerical experiments to validate the method.     

11th international Mach reflection symposium

This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Experiments on the interaction of a pair of cylindrical weak blast waves in air

This paper reports the results of experiments and computations on the interaction of a pair of cylindrical blast waves in air. The waves were generated by exploding wires, and both symmetrical and unsymmetrical interactions were observed. The experimental data includes schlieren photographs of the wave interactions, their radii, shock Mach number and pressure versus time, as well as various cross plots and data on the shock regular/irregular interaction transition condition. The flow fields were computed with the help of the Total Variation Diminishing (TVD) method, and appear to represent the experimental results reasonably well. Some attention is also given to the blast scaling laws of the type discussed by Sakurai (1965) and Oshima (1960).This article was processed using Springer-Verlag TEX Shock Waves macro package 1990.     

Aspect ratio effects in wind tunnel studies of shock wave reflection transition

The transverse wave patterns and flow fields around double wedge experimental arrangements in supersonic facilities for the study of transition from regular to Mach reflection are examined. Guidelines for the minimum inlet aspect ratio to be used are determined in order to ensure that the reflection point is protected from side influences. A preliminary visualization study of the reflection of the wave systems from two wedges of small aspect ratio, has shown the appearance of a new feature in the transition from regular to Mach reflection, that of a dynamic flow distortion, which is presumed to arise due to three-dimensional adjustments in pressure. It occurs in the vicinity of the 2-dimensional mechanical equilibrium point. Oblique shadowgraph images are used to help visualize the flow system. Received 10 December 1996 / Accepted 24 March 1997     

Numerical simulations of shock wave reflection phenomena in non-stationary flows using regularized smoothed particle hydrodynamics (RSPH)

In this paper we wish to demonstrate to what extent the numerical method regularized smoothed particle hydrodynamics (RSPH) is capable of modelling shocks and shock reflection patterns in a satisfactory manner. The use of SPH based methods to model shock wave problems has been relatively sparse, both due to historical reasons, as the method was originally developed for studies of astrophysical gas dynamics, but also due to the fact that boundary treatment in Lagrangian methods may be a difficult task. The boundary conditions have therefore been given special attention in this paper. Results presented for one quasi-stationary and three non-stationary flow tests reveal a high degree of similarity, when compared to published numerical and experimental data. The difference is found to be below 5, in the case where experimental data was found tabulated. The transition from regular reflection (RR) to Mach reflection (MR) and the opposite transition from MR to RR are studied. The results are found to be in close agreement with the results obtained from various empirical and semi-empirical formulas published in the literature. A convergence test shows a convergence rate slightly steeper than linear, comparable to what is found for other numerical methods when shocks are involved.     

Causal Stroh formalism for uniformly-moving dislocations in anisotropic media: Somigliana dislocations and Mach cones

In this work, Stroh’s formalism is endowed with causal properties on the basis of an analysis of the radiation condition in the Green tensor of the elastodynamic wave equation. The modified formalism is applied to dislocations moving uniformly in an anisotropic medium. In practice, accounting for causality amounts to a simple analytic continuation procedure whereby to the dislocation velocity is added an infinitesimal positive imaginary part. This device allows for a straightforward computation of velocity-dependent field expressions that are valid whatever the dislocation velocity–including supersonic regimes–without needing to consider subsonic and supersonic cases separately. As an illustration, the distortion field of a Somigliana dislocation of the Peierls–Nabarro–Eshelby-type with finite-width core is computed analytically, starting from the Green’s tensor of elastodynamics. To obtain the result in the form of a single compact expression, use of the modified Stroh formalism requires splitting the Green’s function into its reactive and radiative parts. In supersonic regimes, the solution obtained displays Mach cones, which are supported by Dirac measures in the Volterra limit. From these results, an explanation of Payton’s ‘backward’ Mach cones (Payton, 1995) is given in terms of slowness surfaces, and a simple criterion for their existence is derived. The findings are illustrated by full-field calculations from analytical formulas for a dislocation of finite width in iron, and by Huygens-type geometric constructions of Mach cones from ray surfaces.     

柱形装药近地动爆冲击波周向传播规律研究

战斗部复杂的末弹道参数会影响近地爆炸冲击波的周向传播规律及对目标的毁伤程度,研究柱形装药近地爆炸冲击波传播规律对精确评估毁伤效能具有重要的工程意义。基于AUTODYN-3D软件对不同末弹道参数的柱形装药近地爆炸进行了数值模拟,通过对2个方向分别建模,获得了柱形装药近地爆炸下前、后、侧3个方向的冲击波压力数据;研究了战斗部的落速、落角、爆心高度和装药长径比4个参数对柱形装药近地爆炸冲击波传播的影响规律,分析了冲击波的演化过程、峰值压力和马赫杆高度。研究结果表明：静爆时,爆心高度是影响冲击波马赫杆高度的主要因素,落角与装药长径是影响马赫杆高度方向差异的主要因素;动爆时,能够增大周向马赫杆高度,前方最显著;另外,随着动爆速度的提升,前向冲击波峰值线性增大。正交优化的结果显示,4种变量中,动爆速度对柱形装药前方峰值压力极差最大,落角对后方峰值压力极差最大,爆心高度对马赫杆高度影响最大。通过研究柱形装药近地动爆冲击波周向传播规律,表明合理的调整装药参数和近地爆炸姿态对实现某方向的最大毁伤或减小超压伤害具有借鉴意义。

     

可压缩混合层流场光学效应分析与实验研究

利用量级分析和风洞实验研究了末制导光学外冷窗口典型流动(可压缩混合层流动)气动光学效应的规律性.理论分析主要针对视线误差(boresight error, BSE)与混合层流场特征参数之间的关系进行了讨论. 研究结果表明: 在可压缩混合层中影响时均BSE的特征参数主要有 对流马赫数、雷诺数、自由流与混合层界面剪切应力、自由流速度比和密度比等因素; 采用细光束穿越混合层流场的风洞试验结果主要证实了时均BSE与对流马赫数之间的关系. 关键词： 气动光学效应 可压缩混合层 对流马赫数     

HL-1M装置边缘等离子体结构研究

描述HL-1M装置上几种典型放电中的边缘等离子体物理实验结果.利用马赫/朗缪尔6探针组、静电4探针组、20组三探针阵列研究了低杂波电流驱动、超声分子束注入、多发弹丸注入和中性束注入放电中的粒子约束性能、等离子体旋转和边缘静电雷诺胁强的变化对改善约束的影响.给出了雷诺胁强和极向相速度的关系.结果表明，雷诺胁强的径向变化可以自发产生托卡马克等离子体的剪切极向流.LHCD能使低密度放电的粒子约束增加1至2倍.弹丸注入后，粒子约束时间和极向旋转至少可增加1倍，而SMBI可使粒子约束时间增加约一个数量级并取得高性能等离子体. 关键词： 粒子约束 雷诺胁强 极向流剪切 马赫/朗缪尔6探针组