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.     

Boundaries of the ambiguity area upon reflection of compression shock waves

Oblique shock waves can be reflected from hard walls, the axis, or the plane of symmetry, as well as from other counterpropagating shock waves with the formation of regular and Mach shock wave configurations. The specific form of shock wave structures is determined by the parameters of the problem: Mach number and intensity of incident shock waves. On the plane of parameters, there exists an ambiguity area in which laws of conservation admit both the regular and Mach reflection of shock waves. The boundaries of this region have been determined.     

Determining integral density distribution in the mach reflection of shock waves

We present a method for and results of determination of the field of integral density in the structure of flow corresponding to the Mach interaction of shock waves at Mach number M = 3. The optical diagnostics of flow was performed using an interference technique based on self-adjusting Zernike filters (SA–AVT method). Numerical simulations were carried out using the CFS3D program package for solving the Euler and Navier–Stokes equations. Quantitative data on the distribution of integral density on the path of probing radiation in one direction of 3D flow transillumination in the region of Mach interaction of shock waves were obtained for the first time.     

超声速半球形多孔探针大气脱体激波仿真研究

为研究半球形多孔探针在超声速大气条件下产生脱体激波的形状和脱体距离随马赫数变化规律,采用CFD方法模拟大气环境,在1.2～1.7马赫数范围内进行数值仿真实验,用双曲线激波形状展示法和最小二乘法拟合得到了激波曲线离心率、脱体距离、曲率半径与马赫数间的函数关系,建立了脱体激波曲线参数化方程。将参数化方程与仿真结果和经验公式比较,结果证明,该参数化方程与仿真结果极为相符,且在距离球体较近处精度较高。参数化方程与经验公式预测的脱体距离差值不超过球体半径的5%。     

The effect of MHD interactions on the input shock waves in a supersonic diffuser

The interaction with an external magnetic field modifies the variation of the shock wave configuration in a pure inert gas plasma at the entrance of a supersonic diffuser. The phenomenon was studied using an experimental setup based on a shock tube with a flat nozzle and the model supersonic diffuser. The experiments were conducted in krypton, for the shock wave Mach number in the shock tube M=7.8 and the Mach number at the nozzle exit M=4.2. The gasodynamic discontinuities and their structural variations induced by the magnetic induction changes were by visualized by the schlieren method and by photography of the intrinsic emission accompanying the process. Three regions of the MHD interaction affecting the shock wave configuration in the gas flow were revealed.     

Outer shock structure of shock-waves propagating in partially ionized gases

Structure of a shock wave propagating through a partially ionized gas is divided into an inner heavy particle shock and two surrounding outer regions. The electron and heavy particle properties are calculated at the two edges of the inner shock and are found to vary, for a given free stream Mach number M₁, almost linearly with the degree of ionization. The Mach number that characterizes the inner shock decreases monotonically from M₁ as the degree of ionization increases and reaches a limiting value, for a given M₁, as the gas becomes fully ionized. The width of the outer regions is found to be of the order of length for electron heat conduction when this conduction is equal to the convected internal energy.     

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.     

SCALING LAWS FOR PARTICLE BREAKUP IN NOZZLE GENERATED SHOCKS

Conditions for the onset of particle breakup in normal shock waves have been investigated. A normalized particle drag behind the shock has been determined in terms of gas stagnation conditions and particle diameter for a range of gas Mach numbers 1 ≤ M₁ ≤ 5 by introducing appropriately defined particle Knudsen and Reynolds numbers into analytical expressions for the drag coefficient. Numerical computations of the particle drag, normalized with gas stagnation pressure and particle area, indicate a peak at a gas Mach number M₁ ≳ 2.2, The magnitude of the peak was found to decrease with increasing particle diameter and reservoir gas density.

Criteria for the onset of agglomerate breakup were defined in terms of a modified Weber number for the adhesion mechanisms due to Van der Waals forces, electrostatic attraction and adsorbed surface films. These results indicate that larger more closely packed agglomerates made up of smaller constituent particles have a greater tendency to resist breakup for a given set of stagnation conditions and shock Mach number.     

Experimental investigation of drag reduction by forward facing high speed gas jet for a large angle blunt cone at Mach 8

Substantial aerodynamic drag, while flying at hypersonic Mach number, due to the presence of strong standing shock wave ahead of a large-angle bluntcone configuration, is a matter of great design concern. Preliminary experimental results for the drag reduction by a forward-facing supersonic air jet for a 60° apexangle blunt cone at a flow Mach number of 8 are presented in this paper. The measurements are carried out using an accelerometer-based balance system in the hypersonic shock tunnel HST2 of the Indian Institute of Science, Bangalore. About 29% reduction in the drag coefficient has been observed with the injection of a supersonic gas jet.     

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.     

The specifics of the shock compression of matter in cylindrical bombs

The dynamic pattern of the shock compression of a substance in cylindrical bombs is examined. It is demonstrated theoretically and experimentally that conditions are established in the center of the bomb for nonregular Mach repulsion.     

Numerical investigation of the onset of instability of triple shock configurations in steady supersonic gas flows

Triple configurations of shock waves that arise in a steady supersonic flow of a real gas have been numerically simulated. Previously, we have theoretically predicted that a new triple shock configuration with a negative reflection angle can appear in a gas flow at large Mach numbers and small adiabatic indices. This configuration is now obtained for the first time in numerical experiments. It is shown that the formation of this triple shock configuration leads to instability of the entire flow pattern.     

Mathematical models of supersonic and intersonic crack propagation in linear elastodynamics

International Journal of Fracture - This paper presents mathematical models of supersonic and intersonic crack propagation exhibiting Mach type of shock wave patterns that closely resemble the...     

Coefficients of transformation of long-wavelength perturbations of a supersonic incident flow around a wedge into pressure fluctuations on its surface

The interaction of different types of long-wavelength perturbations of a supersonic incident flow around a wedge with an arising shock wave is simulated numerically. The results of parametric calculations are compared with the data of the linear theory for the interaction of perturbations with a shock wave in the absence of a body. Data on the structure of pressure fluctuations behind the shock wave on the wedge and data on the coefficients of transformation of external perturbations represented in the form of analytical dependences on the angle of inclination of the shock wave, the angle of propagation of external perturbations, and the incident Mach number are obtained.     

Translational nonequilibrium of the shock wave front in an argon-helium gas mixture

It is experimentally established that the concentration of metastable atoms appearing in the front of a shock wave propagating in a gas phase is greater by one order of magnitude for an argon-helium 1: 1 mixture than for pure argon with the same Mach number and initial pressure. The average “longitudinal” temperature of the shock wave front is determined. An expression for the concentration of excited particles is derived that takes into account the “ longitudinal” character of the gas temperature in the shock wave front.     

内埋武器发射参数对下落轨迹的影响

采用改进的延迟分离涡模拟方法结合动网格技术,对某一简化内埋弹舱-舱门-弹体模型的三维流场进行非定常计算,得到了不同来流马赫数、弹体发射速度和初始角速度等参数对弹体下落轨迹的影响规律。结果表明:亚声速条件下来流马赫数对弹体偏航角度影响较小,跨声速及超声速条件下受流场波系的影响,弹体均向右偏航。超声速条件下,随马赫数增加弹体偏航角和俯仰角的变化幅度减小。提升弹体初始发射速度可以使弹体快速达到安全分离距离,并减小姿态角变化。增加弹体初始低头角速度可以在不增加弹射力的情况下,减小弹体俯仰角度,提高弹体分离速度,有利于机弹安全分离。     

Effect of shock waves outgoing from partly blocked channel upon an obstacle

Partial channel blocking affects the relative contributions of shock waves and concurrent jet flow. This results in decreasing or increasing the dynamic shock-wave action upon an obstacle, depending on the duration of action and the Mach number.     

Rearrangement of the shock wave structure in a decaying discharge plasma

A study has been made of the change in the structure of a shock wave in a decaying discharge plasma with Mach numbers between 1.2 and 2. A novel method is proposed to investigate the rearrangement of the shock wave structure under transient conditions. The times of the main processes responsible for this effect are determined. Pis’ma Zh. Tekh. Fiz. 23, 18–22 (April 12, 1997)     

物理靶上自由飞流场全息干涉诊断

在马赫数为15的条件下,采用激光全息干涉技术在物理靶上拍摄到直径12mm的球标模自 由飞流场全息干涉图和阴影照片。通过干涉照片获得了流场中六个截面的密度分布曲线,同时从阴影照片上测量出弓形激波的归一化脱体距离为0.046。将实验照片与计算流场干涉图进行比较,二者的激波位置、条纹变化量及条纹连接基本一致。     

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.