Reflection of an air shock wave from a foam layer

Within the framework of an equilibrium model of disperse media, the problem on reflection of an air shock wave from a foam layer located in the neighborhood of a rigid wall is investigated. An exact solution is constructed for the initial stage of reflection from a homogeneous layer. The effect of the type of gas which fills foam bubbles on the characteristics of reflected waves is studied. The results of numerical calculations are given, which are obtained using the modified Godunov method     

Evaluation of glycerol viscosity through the width of a weak shock wave

Measurements of the width of a shock wave in glycerol dependent on the pressure of shock compression were taken to improve the method of determination of liquids viscosity. It was found that the time of growth of parameters in a shock wave decreases to the limit of time resolution of modern measurements, which is approximately 1 ns at the shock compression pressure of around 2.5 GPa. The values of viscosity, obtained at these parameters, are in agreement with experimental data. The transition to stepwise shock compression expands the pressure range, available for measurement by this method, and also makes possible the opportunity to vary the temperature.     

Decreasing the action of a flow behind a weak shock wave emerging from a channel upon an obstacle

It is experimentally demonstrated that, if the flow behind shock waves outgoing from a channel is subsonic, the action of this flow upon an obstacle can be decreased by changing the shape of the output channel cross section. The results of numerical modeling of the experimental oscillograms show that, by replacing a round channel with a cross-shaped one, the excess action upon the obstacle in a quasi-stationary stage can be reduced by half. This decrease is related to energy dissipation in a three-dimensional flow as a result of the interference of rarefaction and compression waves. The interference arises due to mass redistribution between various symmetry axes in the gaseous medium and due to the flow energy losses for the vortex formation at the channel edges, which are revealed by schlieren photographs.     

Damage to an electric double layer by a weak shock acoustic wave

Results are presented of experimental investigations of the dynamics of the electrical conductivity of an electrolyte when one of the electrodes is exposed to a weak shock pulse. It is shown that the electrical conductivity in the cell increases as a result of damage to the electric double layer. Pis’ma Zh. Tekh. Fiz. 25, 20–23 (January 26, 1999)     

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.     

Interaction between a weak oblique shock wave and a turbulent boundary layer in purely supersonic flow

Summary The paper deals with the interaction of a weak oblique shock and a turbulent boundary layer at a flat plate at purely supersonic speeds. Except for a small region where nonlinear transonic effects are of importance analytical expressions for the pressure- and skin friction distributions are derived.With 6 Figures     

Shape optimization of one‐chamber perforated plug/non‐plug mufflers by simulated annealing method

To economically and efficiently lower the venting noise, the development of a high‐quality muffler with compact volume has become crucial in the modern industrial field. The research work of shape optimization of straight silencers in conjunction with plug/non‐plug perforated ducts which may noticeably increase the acoustical performance is rarely addressed; therefore, the main purpose of this paper is not only to analyze the sound transmission loss (STL) of a one‐chamber plug/non‐plug perforated muffler but also to optimize the best design shape under a limited space. In this paper, on the basis of plane wave theory, the four‐pole system matrix in evaluating the acoustic performance is derived by using the decoupled numerical method. Moreover, a simulated annealing (SA) algorithm searching for the global optimum by imitating the softening process of metal has been adopted during the muffler's optimization. To assure SA's correctness, the STL's maximization of one‐chamber perforated plug mufflers at a targeted frequency of 500 Hz is exemplified first. Furthermore, a numerical case in dealing with a broadband noise emitted from a fan by using one‐chamber plug/non‐plug mufflers has been introduced and fully discussed. To achieve a better optimization in SA, various SA parameter sets of cooling rate and iteration parameter values were used. Before the SA operation can be carried out, the accuracy check of the mathematical models with respect to plug/non‐plug perforated mufflers has to be supported by experimental data. The optimal result in eliminating broadband noise reveals that the muffler with a plug acoustical mechanism has a better noise reduction than that of a non‐plug muffler. Consequently, the approach used for the optimal design of the noise elimination proposed in this study is certainly easy, economical, and quite effective. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis of oblique wave interaction with a submerged perforated semicircular breakwater

This study examines oblique wave interaction with a submerged perforated semicircular breakwater based on the linear potential theory. The fluid domain is divided into inner and outer regions by a perforated semicircular arc. The velocity potentials in the inner and outer regions are constructed by eigenfunction expansions and multipole expansions, respectively. The unknown constants in the velocity potentials are determined by matching the boundary conditions on the perforated arc. The convergence of the solution method we have developed is rapid. The reflection and transmission coefficients and the wave forces acting on the breakwater are calculated and examined. Some useful results are presented for practical engineering.     

Initiation of detonation in reflection of a shock wave from a concave curvilinear surface

The authors present results of investigating the possibility of initiating a detonation regime of combustion of reactive gaseous mixtures by focusing a plane shock wave in reflection from concave axisymmetric and two-dimensional surfaces.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences of Belarus, Minsk. Scientific-Production Company Prostor, Krasnoarmeisk, Moscow Region. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 66–72, July–August, 1994.     

Calculation of heat flux from the region behind a reflected shock wave into the shock tube edge

We have numerically calculated the process of conjugated unsteady heat exchange during the formation of a boundary transient temperature layer as a result of the interaction of a shock wave with a flat edge surface of a shock tube. The results of calculations can be used in the analysis of the experimental data. The time variation of the heat flux and the temperature at the gas-solid interface is determined. The heat flux distribution profiles are obtained for two limiting variants of the boundary conditions on the outer surface of the shock tube.     

Interaction of a shock wave with a tangential discontinuity

The interaction of the shock wave receding from an obstacle with the line of a tangential discontinuity is investigated for unrated supersonic jets. It is suggested that one of the causes of strong instability of the wave structure of the jet at certain positions of the obstacle may be the incompatibility of conditions from different sides of the tangential discontinuity at the intersection of the latter with the shock wave.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 21, No. 2, pp. 251–256, August, 1971.     

Diamond synthesis by weak shock loading

A hexagonal polymorph of diamond has been synthesized by relatively weak shock loading (in a range of projectile velocity 0.655 to 1.88 km sec^–1) with a recovery technique. Four mixtures of copper with spectroscopic graphite, amorphous carbon, glassy carbon and graphite fluoride, with densities of 4.8 to 7.8 g cm^–3, were used to control the shock temperature rise and to quench efficiently. Spectroscopic graphite gave the maximum yield of diamond (8%). Chaoite was also observed in the shocked amorphous carbon and glassy carbon. A local temperature rise during shock was inferred from the temperature of some spherical particles, indicative of superheating of the particles to near or above the melting point.     

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.     

Skew shock wave on a gas-solid body interface

The interaction between a skew shock wave (SSW) and a plane surface of a solid body is considered. Break decay (BD) on the gas—solid body interface at an arbitrary angle of impact is calculated within the limits of applicability of the hydrodynamic theory of shock waves.     

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.     

Automatic extraction and registration of shock wave fronts from series interferograms of a flow field

Algorithms for extracting shock wave fronts from interferograms of a flow field and for registering time-series shock waves are proposed. Based on these, application software is developed on a PC-Vision 100 image-processing system. As application examples, interferograms of a primary high-explosive flow field and a real, solid rocket muzzle flow field are processed. The results indicate that the propagation velocity of the shock wave can be easily calculated with this method.     

On the propagation of a weak shock front: Theory and application

Summary In this paper the kinematics of a weak shock front governed by a hyperbolic system of conservation laws is studied. This is used to develop a method for solving problems, involving the propagation of nonlinear unimodal waves. It consists of first solving the nonlinear wave problem by moving along the bicharacteristics of the system and then fitting the shock into this solution field, so that it satisfies the necessary jump conditions. The kinematics of the shock leads in a natural way to the definition of shock-rays, which play the same role as the rays in a continuous flow. A special case of a circular cylinder introduced suddenly in a constant streaming flow is studied in detail. The shock fitted in the upstream region propagates with a velocity which is the mean of the velocities of the linear and the nonlinear wave fronts. In the downstream the solution is given by an expansion wave.With 7 Figures     

Similarity solutions for two-dimensional weak shock waves

The general forms of self-similar solutions for two-dimensional weak shock waves in fluid dynamics are obtained. The functional form describing the area under the initial pulse is characterized under which the general system of PDEs admits similarity solutions. It is shown how one can construct new solutions with shock discontinuity from these self-similar solutions. In particular, a plane-wave solution is joined with a self-similar solution across a non-trivial shock. Furthermore, a new class of non-trivial simple wave solutions is presented.