State-of-the-art in research on Mach reflection of shock waves

Reflected shock transition from Mach to regular reflection over wedges and state-of-the-art of Mach reflection research are presented. Examples of shock wave reflection from multiple wedges and curved wedges are given in conjunction with the Mach reflection research.     

TNT装药爆炸波在刚性平面上方传播反射的数值研究

为研究爆炸冲击波传播和平面反射现象,运用显式非线性动力有限元软件ANSYS/LS-DYNA对柱形TNT装药在刚性平面上方爆炸产生的冲击波的传播和反射进行了数值模拟,将数值计算结果与试验结果和公式计算值进行了对比,结果表明利用数值模拟能够较好地反映压力场分布情况及爆炸冲击波传播、正反射、正规斜反射到马赫反射的演变过程;研究了装药形状对反射平面测点超压的影响。     

Critical angle of regular interaction upon collision of two unidentical strong skew shock waves in a gas with a constant polytropic index

In the present work on the basis of relationships of the hydrodynamic theory of shock waves, the author determines a critical angle of existence of a regular collision regime (RCR) for two unidentical plane skew shock waves (SSW) in a gas, the change in the polytropic index of which behind the shock wave front can be neglected.     

Formation of triple shock configurations with negative reflection angle in steady flows

Triple configurations of shock waves with negative reflection angles are considered. These configurations have been observed in quasi-steady cases of shock wave reflection from a planar wedge in real gases, while in steady cases three-shock configurations are only known to occur with positive reflection angles. Boundaries for the appearance of a three-shock configuration with a negative reflection angle in steady cases are analytically determined as dependent on the initial Mach number of the flow, angle of incidence, and adiabatic index. The formation of a three-shock configuration with a negative reflection angle in a steady flow must lead to a change in the character of the wave pattern, and under certain conditions it can lead to instability.     

Nonstandard analysis of a converging shock wave in a nonideal gas

The problem of propagation of strong plane and converging shock waves in an unsteady inviscid nonideal gas is studied. A nonstandard analysis is used to derive the jump conditions for both shock waves. It is assumed that the jump occurs on an infinitesimal interval and jump functions in the flow parameters are smooth across this interval. The distribution of the flow parameters across the shock wave is expressed in terms of the Heaviside functions. Numerical computation to study the distribution of the flow parameters is performed.     

Propagation of weak discontinuities along the bicharacteristic curves in a vibrationally relaxing gas

The transport equations representing the rate of change of discontinuities in the normal derivatives of flow parameters are obtained along bicharacteristic curves in the characteristic manifold of the differential equations governing the flow of a vibrationally relaxing gas, an explicit criterion for the growth and decay of weak discontinuities along bicharacteristics is given and the specialization is made to the waves of plane, cylindrical and spherical geometry. It is investigated as to how the effects of vibrational relaxation, the magnitude of the initial discontinuity, the initial curvature of the wave front, and the upstream flow Mach number will influence the growth and decay properties of the wave front.     

Optical diagnostics of dynamic structures in shock waves

We demonstrate the possibility of applying optical diagnostics based on laser Doppler anemometry techniques and the laser imaging of dynamic density fields to the investigation of kinematic and structural parameters of shock waves and the properties of air perturbed by shock waves. Using the proposed methods, dynamic structures in the shock wave have been revealed and the velocity of their motion over the wave front has been determined. It is suggested that these dynamic structures have an oscillatory nature.     

Formation of cylindrical shock waves in radiation-magneto gas dynamics

The propagation of acceleration waves in radiation-magneto gas dynamic flow which is induced by the motion of a piston advancing with finite acceleration into a constant state of rest has been studied along with the characteristic path by using the characteristics of the governing quasilinear system as the reference coordinate system. It is shown that a linear solution in the characteristic plane can exhibit nonlinear behaviour in the physical plane. A differential equation governing the growth and decay of an acceleration wave is derived. The critical time is obtained when all the characteristics will pile up at the wave front to form a shock wave. It is found that the effect of magnetic field on compressive waves which owe their origin to radiation is to cause an early shock formation, while on those of expansion waves which owe their origin to radiation the effect of magnetic field is to decrease the decay rate. However, the effect of coupling of radiation and magnetic field on waves (compressive) which are emanating from piston movement is to slow down the motion of a breakdown point and thus increase the cylindrical shock formation time, while on those of expansion waves, the effect is to enhance the decay rate.     

Localization of pulsed energy deposition in a transverse surface discharge initiated in a gas flow with shock wave

The localization of a nanosecond transverse surface discharge initiated in a plasma sheet sliding over a dielectric surface in a channel featuring gas flow with a plane shock wave has been studied by monitoring glow intensity distribution at the discharge-ionized channel surface in the presence of the shock wave. Judging from the glow pattern, the entire energy of discharge is usually localized in a low-pressure region in front of the propagating shock wave. The density of energy deposited in front of the shock wave can be varied (in particular, increased up to 12–15 eV per particle) by initiating the discharge at various positions of the shock wave. Transitions from the discharge with glow localized sharply in front of the shock wave to the regimes with glow extended behind the front or with a volume glow region ahead of the shock wave were observed for certain values of the Townsend parameter (E/P) and Mach number (M).     

Experimental study of the pressure field of an electric explosion of plane ring foil

Results of an experimental study of the pressure field of a shock acoustic wave in a closed chamber with condensed matter are presented; this wave results from the electric explosion of a plane ring foil, on which discharge current passes in the radial direction. The presence of a pronounced pressure maximum with regard to the electrode-system axis can be interpreted as the effect of nonlinear interaction of elements of the shock acoustic waves excited on diametrically opposite sides of the exploding ring foil.     

Mach number distribution over the axis of supersonic underexpanded jets

The limiting flow parameters are determined directly behind the central shock for Mach numbers M ? 1 in front of the shock. A formula for the Mach number distribution over the jet axis is derived.     

Effects of a small airfoil-shaped splitter plate on vortex shedding from a square prism at subsonic Mach numbers

Summary The present study is concerned with effects of a small airfoil-shaped splitter plate (NACA 0018, chord lengthc=20 cm) on the vortex shedding from a single square prism (side lengthD=20 mm) at free-stream Mach numbers between 0.15 and 0.91 and a constant spacing ratioL/D=2.0, whereL is the central distance between the square prism and airfoil arranged in tandem.It is found that while there exist no shock waves in the flow the vortex shedding from a single square prism is retarded by the small airfoil due to the interaction with the upper and lower separating shear layers: The Strouhal number for the square prism and airfoil being arranged in tandem, is almost independent of the Mach number and takes about 0.11. This is smaller than the value of 0.13 known for a single square prism. However, as soon as shock waves appear in the flow, the Strouhal number increases suddenly and then increases with increasing the Mach number. It is inferred that the sudden increase of the Strouhal number is primarily caused by shock waves appearing above and below the vortex formation region, for the shock waves make the vortex formation region small and symmetrical with respect to the common axis of the square prism and airfoil. That means, the small airfoil causes only a secondary effect on the vortex shedding from a single square prism under the presence of shock waves in the flow.     

建筑物内爆泄压口冲击波参数工程算法研究

建筑物内部爆炸泄压口冲击波参数的确定对于建筑物结构毁伤评估具有重要的作用,一旦泄压口冲击波参数确定以后,即可利用相应毁伤判据快速评估泄压口附近结构和设备的毁伤程度。由于内部爆炸波是初始爆炸波经过建筑物内壁面多次反射叠加作用的结果,在泄压口会形成不同于自由场的冲击波,目前还未有泄压口冲击波参数成熟的快速工程算法。为了分析泄压口冲击波参数、总结相应快速经验工程算法,本文在量纲分析的基础上,提出影响泄压口冲击波峰值压力和冲量相关的无量纲参数。然后利用首先利用AUTODYN软件数值仿真研究了特定当量内爆炸作用下冲击波形成的过程,分析了泄压口部冲击波压力波形,并研究了泄压口的冲击波峰参数与不同结构参数之间的关系,最后在大量数值计算的基础上总结了泄压口的冲击波参数的经验公式,为建筑物内爆毁伤评估奠定基础。     

On the propagation of harmonic plane waves under the two-temperature theory

The propagation of harmonic plane waves in media described by the two-temperature theory of thermoelasticity (2TT) is investigated. Exact dispersion relation solutions are determined and several characterizations of the wave field are examined. High- and low-frequency results are given and special/limiting cases are also noted and discussed. In addition, critical values of the physical parameters are determined, as well as their impact on the wave fields, and the dispersion characteristics of such media are established.     

On the form of the elastic potential relative to different reference states

Summary Using the method of wavefront analysis the paper presents an analysis of shock wave formation in a two-dimensional steady supersonic flow of a radiating gas past plane and axisymmetric bodies such as a beak and sharp edged ring. Transport equations are derived which lead to the determination of the shock formation distance and also to conditions which insure that no shock will ever evolve on the wavefront. It is assessed as to how the shock formation distance is influenced by the presence of thermal radiation, the initial body curvature and upstream flow Mach numberM ₀>1.With 1 Figure     

Peculiarities of reflected shock wave bifurcation on a needle

The axisymmetric bifurcation of a reflected shock wave interacting with the boundary layer on a 79-mm-long needle with a diameter of 1.1 mm has been studied. The needle, oriented in counterflow direction, was mounted at the axis on the end wall of a shock tube with 98 × 98-mm section. Experimental data on the parameters of reflected shock wave bifurcation are presented for CO₂ at an initial pressure of 4 kPa and Mach number M = 2.5 of the incident shock wave. The obtained data are compared to experimental parameters of the reflected shock wave bifurcation on side walls of the shock tube. Experimental data were obtained by schlieren imaging of flow patterns and high-speed photography with a DICAM-Pro camera in the double-frame recording mode.     

On the behavior of shock waves in deformable dielectric materials

In this paper, the behavior of plane shock waves propagating in elastic dielectrics is examined. The differential equation governing the amplitude of wave and formulae concerning the polarization changes across the shock are deduced. Some particular situations are studied in detail.     

The antimicrobial action of high-power electric discharge in water. Part 1. Shock wave initiation,evolution, and structure

We have studied the initiation, evolution, and structure of shock waves as the main antimicrobial factor of a high-power electric discharge in water. The shock wave structure is studied in a plane one-dimensional approximation using a system of generalized equations of hydrodynamics proposed by Alekseev. Possible mechanisms of the shock-wave-induced degradation of microorganisms are considered.     

The formation of vortex shocks in a 3D subsonic flow behind a weak shock wave emerging from a channel

The structure of a 3D subsonic flow behind a diffracted shock wave was studied by experimental and numerical methods for the incident shock wave Mach numbers M ₀ close to unity. It is established that vortex shocks appear in the flow behind the diffracted shock wave even when M ₀ decreases to 1.04, which is much lower than the threshold Mach number obtained analytically for a 2D automodel case. The time interval from the outflow start to the local supersonic zone formation, as well as the experimentally measured time of appearance of the first vortex shock, increase with decreasing M ₀.     

Effect of focusing conditions on laser-induced shock waves at titanium-water interface

The spatial and temporal evolution of laser-induced shock waves at a titanium-water interface was analyzed using a beam deflection setup. The focusing conditions of the source laser were varied, and its effect onto the dynamics of shock waves was elucidated. For a tightly focused condition, the speed of the shock wave was ~6.4 Km/s, whereas for a defocused condition the velocities reduced to <3 km/s at the vicinity of the titanium-water interface. When the laser is focused a few millimeters above the target, i.e., within the water, the emission of dual shock waves was observed toward the rear side of the focal volume. These shock waves originate from the titanium-water interface as well as from the pure water breakdown region, respectively. The shock wave pressure is estimated from the shock wave velocity using the Newton's second law across a shock wave discontinuity. The shock wave pressure for a tightly focused condition was 18 GPa, whereas under a defocused condition the pressure experienced was ≤1 GPa in the proximity of target.