Amplification of Vortex and Temperature Waves in the Process of Induced Scattering of Sound in Thermodynamically Nonequilibrium Media

The unsteady-state induced scattering of sound by vortex and temperature waves in gas media is studied. It is shown that, in thermodynamically nonequilibrium media that are acoustically active, the parametric increment may be much higher than that in equilibrium media. This is accompanied by a sharp growth of amplitudes of vortex and temperature waves.     

Interaction of a characteristic shock with a weak discontinuity in a relaxing gas

The evolution of a characteristic shock in a relaxing gas is investigated and its interaction with a weak discontinuity is studied. A particular solution to the governing system, which exhibits space–time dependence, is used to study the evolutionary behaviour of the characteristic shock; the properties of incident, reflected and transmitted waves, influenced by the relaxation mechanism, together with the geometry of the fluid flow and the background state at the rear of the shock, are studied.     

Shadow photoelectric method for determining the refractive index of a gas flow behind a shock wave

A quantitative shadow photoelectric method for the investigation of transient processes is described. The capabilities of the method are illustrated in the example of investigations of high-temperature gas flows behind strong shock waves in shock tubes and the determination of the refractive index and its gradient in the zone of nonequilibrium processes following a shock wave.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 21–23, July, 1994.     

The Evaporation of Quartz Particles behind Strong Shock Waves in Slightly Dusty Air

Parametric calculations are performed of the evolution of micron spherical particles of quartz dust in a high-temperature air flow behind strong shock waves with the forward flow velocity ranging from 1.6 to 2.6 km/s (6 < M < 9) and the altitude ranging from 15 to 20 km in the Earth's atmosphere. The calculation results are used to determine the limits of the characteristic states of partial and complete evaporation of the disperse phase. The model of the processes of nonequilibrium energy transfer includes vibrational relaxation in the gas phase, heterogeneous relaxation involving the dispersed phase, heating, sublimation, melting, evaporation, and equilibrium radiation of particles.     

Equilibrium spectral radiation behind the shock wave front in a CO2-N2 gas mixture

This paper presents calculations of the equilibrium spectral radiation behind shock waves in a CO₂-N₂ gas mixture, corresponding to the conditions implemented in experiments with NASA Ames Research Center and JAXA Chofu Space Center shock tubes. The studied experimental parameters were selected so that the results obtained for these systems can be cross-validated. The presented data for equilibrium spectral radiation were obtained using two methods for calculating the equilibrium populations of the excited electronic states, based on a hybrid radiative-collisional model (in fact, a model of nonequilibrium radiation) and on the use of the Boltzmann distribution with the calculated equilibrium temperature. The spectral composition of the radiation was also analyzed; a comparison of the calculated and experimental data demonstrated reasonable agreement between them.     

Transition from acceleration waves to strong discontinuities in fluid-saturated solids: drained versus undrained behaviour

The evolution of compression waves propagating in a fluid-saturated granular solid is considered. The pore fluid is assumed to consist of a liquid with a small amount of free gas. The stiffness of such a solid increases with increasing pressure. This property leads to the transformation of continuous compression waves into shock fronts after a finite time of propagation. The aim of the study is to calculate the critical distance covered by a continuous wave before it loses continuity. Critical distances are calculated for weak discontinuities (acceleration waves) propagating into a quiescent region. In numerical examples, the pressure dependence of the stiffness is taken in a form typical of granular solids. Emphasis is placed on the influence of free gas in the pore fluid and the permeability of the skeleton. Comparison of locally undrained and drained behaviour reveals that the drained model with low permeability turns out to be misleading for the calculation of the critical distance of a compression wave.     

Shock waves in an elastic pipeline

The formation of shock waves from the solitary Gaussian and hyperbolic waves in an elastic pipeline has been investigated. It is shown that the parameters of these waves — the path length and the time of formation — differ insignificantly from the analogous parameters of the shock waves formed from the sine waves. The evolution of the discontinuity surface in these shock waves has been considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 3, pp. 489–495, May–June, 2008.     

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.     

Mechanisms of development of superhigh pressures under conditions of propagation of explosion waves in conical cavities

In this study, numerical simulation methods are used for investigating the processes of propagation in a conical cavity (conical target) of weak shock waves caused by the blast of a microcharge in combustible mixture outside of the cone volume. A more general question is considered: how do the parameters of the medium at the cone vertex depend on whether it was a neutral gas (air) or combustible mixture (hydrogen-air) that filled the cone initially? Comparison is made of the maximal attainable pressures in the cases where the cone is filled with a combustible mixture and in the cases where the cone contains a neutral gas (air). The leading physical factors are identified and substantiated, which provide for attaining extremely high pressures in narrowing volumes. The problem under consideration is of applied importance from the standpoint of predicting the development of emergencies caused by the propagation of explosion waves in volumes filled with combustible gas.     

Characteristics of the effect of low-current gas discharge on a strong shock wave

The effect of nonequilibrium plasma medium created by low-current gas discharge on a shock wave (Mach number M = 6.8) has been investigated. The shock wave is generated in a shock tube with a circular cross section and then passes through the area of the effect in the working chamber having a square cross section. The gas discharge is ignited in the area of the effect before the arrival of the shock wave by applying voltage to special pin electrodes mounted in the upper and lower walls of the working chamber. In the experiment, the phenomenon of broadening of the shock wave and an increase of its propagation velocity when passing through the region of nonequilibrium gas-discharge plasma was discovered.     

Some Aspects of Treatment of Plastic Powders by Skew Shock Waves

A method for estimating the hydrodynamic parameters of powder and porous materials behind the front of shock waves formed as a result of break decay in emergence of a skew shock wave on the interfaces between these materials or between them and other media is proposed.     

Gasdynamic phenomena accompanying the motion of shock waves and objects in a low-temperature nonequilibrium plasma

An analysis is made of gasdynamic anomalies observed during the motion of shock waves and objects in a low-temperature nonequilibrium plasma. It is shown that these anomalies are associated with behavior of sound propagating in a nonequilibrium plasma. Pis’ma Zh. Tekh. Fiz. 24, 44–49 (September 26, 1998)     

Shock waves in multi-component “liquid — gas bubbles — liquid drops” media

Shock waves are experimentally investigated in multi-component “liquid — gas bubbles — liquid drops” media. The data are obtained on the shock wave structure and properties in these multi-component media.     

Effect of disperse phase on instability in systems with combustion

The dynamics of weak perturbations with finite amplitude in a two-phase homogeneous medium (gas with suspended solid particles) featuring a nonequilibrium chemical reaction has been studied. Using an asymptotic approach, a weakly nonlinear model of the evolution of one-dimensional perturbations is developed that takes into account the kinetic wave interactions and dissipative properties including the interphase exchange of heat and momentum. Conditions for the loss of stability of the homogeneous state of the system are analyzed. Numerical solutions of the evolution equation are obtained in the form of established self-sustained oscillations. The stabilizing effect of the inert disperse phase is described.     

Self-ignition of hydrogen-air mixtures behind reflected explosive waves

Experimental results are given, which reveal the special features of selfignition of hydrogen-air gas mixtures behind reflected explosive pressure waves at moderate (below 1200 K) temperature and elevated pressure. The experiments are performed in a modified shock tube which provides for generation of explosive pressure waves. The explosive waves are characterized by a jump of parameters of shock-compressed gas (pressure, temperature) at the front with their subsequent continuous decrease. This is how undesirable gas-dynamic effects are attenuated, which are due to hypothetical pre-explosion preheating of combustible mixture by compression waves. As previously, the experiments involving standard shock waves (with constant pressure/temperature levels) revealed a significant (by a factor often and more) deviation of measured values of delay of selfignition from the calculated values towards decreasing.     

Numerical analysis of strongly nonlinear extensional vibrations in elastic rods

In the framework of transduction, nondestructive testing, and nonlinear acoustic characterization, this article presents the analysis of strongly nonlinear vibrations by means of an original numerical algorithm. In acoustic and transducer applications in extreme working conditions, such as the ones induced by the generation of high-power ultrasound, the analysis of nonlinear ultrasonic vibrations is fundamental. Also, the excitation and analysis of nonlinear vibrations is an emergent technique in nonlinear characterization for damage detection. A third-order evolution equation is derived and numerically solved for extensional waves in isotropic dissipative media. A nine-constant theory of elasticity for isotropic solids is constructed, and the nonlinearity parameters corresponding to extensional waves are proposed. The nonlinear differential equation is solved by using a new numerical algorithm working in the time domain. The finite-difference numerical method proposed is implicit and only requires the solution of a linear set of equations at each time step. The model allows the analysis of strongly nonlinear, one-dimensional vibrations and can be used for prediction as well as characterization. Vibration waveforms are calculated at different points, and results are compared for different excitation levels and boundary conditions. Amplitude distributions along the rod axis for every harmonic component also are evaluated. Special attention is given to the study of high-amplitude damping of vibrations by means of several simulations. Simulations are performed for amplitudes ranging from linear to nonlinear and weak shock.     

Resonant interaction of acoustic waves in nonequilibrium gases

Nonlinear equations are derived, which describe the evolution of two-dimensional acoustic disturbances in a thermodynamically nonequilibrium gas. The characteristic features of parametric interaction of wave packets in acoustically active media are analyzed. The transmission band under conditions of critical and noncritical matching and the threshold of parametric amplification are determined. Conditions are obtained, under which a giant parametric pulse may form in an acoustically active medium, with the amplitude of this pulse exceeding that of a pumping wave.     

On the question of universality of imploding shock waves

For the case of initially infinitesimally weak spherically and cylindrically imploding shocks, Ponchaut et al. (J. Fluid Mech., 560:102–122, 2006) recently obtained universal solutions. We study the effect of starting the shock with an initially finite strength on the trajectory of the shock by performing numerical calculations for the incoming shock imploding spherically into a diatomic perfect gas. Deviations from the universal solution are extremely small. A solution for the initially infinitesimally weak shock obtained by using Whitham’s (Linear and nonlinear waves, Wiley, New York, 1974) Shock Dynamics is virtually indistinguishable from the Ponchaut solution.     

Similarity solution and wave propagation in a reactive polytropic gas

We consider similarity solutions of the ZND model for detonation waves. Assuming as boundary condition the RH relations for the precursor shock, we obtain exact similarity solutions corresponding to reaction rates compatible with the associated stretching group of transformations which leaves invariant the governing system. The location of weak discontinuities across a similarity line and their evolution laws are determined.     

Influence of the Curvature of an Airfoil on the Structure of Transonic Flow

A study is made of the dependence of the pattern of transonic flow about an airfoil on the change in its shape and in the parameters of the incoming air flow. Consideration is given to a family of airfoils in a channel modeling the working section of a wind tunnel. The formation and propagation of weak shock waves in local supersonic regions near the central part of the airfoil has been investigated numerically. The finite-difference method based on a substantially nonoscillatory scheme of second order of accuracy has been employed to solve the Euler equations describing nonviscous gas flow. It has been shown that the sensitivity of the flow pattern to a change in the Mach number of the free flow substantially increases with decrease in the curvature of the airfoil.