Home – Home – Jornals – Combustion, Explosion and Shock Waves 2013 number 4

The dynamics of the structure of a cavitating magma flow behind the decompression wave front is experimentally studied by the method of hydrodynamic shock tubes. It is demonstrated that a discrete system of intensely cavitating zones with alternation of low and high densities of the gas phase can be formed at a certain regime of shock-wave loading of the examined fluid sample. Based on the results of a numerical analysis of the formation of an anomalous zone in the cavitating magma flow with anomalously high flow characteristics exceeding the values of these characteristics outside this zone at least by an order of magnitude, a model of an instantaneous transformation of the cavitating magma in the anomalous zone to a gas-droplet system, its ejections, and formation of a free surface on the interface is proposed. A numerical analysis shows that the characteristic wave structure and the anomalous saturation zone are fairly rapidly reconstructed in the vicinity of this free surface of the flow part remaining in the conduit after the ejections, and the above-mentioned jumps of flow characteristics are again formed in the anomalous zone.

This paper considers a range of physical phenomena that occur during electrical discharge in water in the presence of a transverse magnetic field. An approximate equation of energy balance is obtained using assumptions based on the well-known hydrodynamic concepts of a long electrical discharge in water. An experimental estimate of the reaction force impulse in a limited medium is obtained.

Two types of electric discharges to be used for the purpose of air flow control are compared. The parameters measured in experiments are the electric characteristics of the discharges and the velocity of flows generated by them. The ionic wind velocity in the sliding discharge is demonstrated to be smaller than in the dielectric barrier discharge. The volume forces acting from the discharge on air and the efficiency of the electro-gas-dynamic action are estimated. The presence of an additional electrode in the case of the sliding discharge is found to affect the distribution of the spatial charge and change the forces, leaving the electric characteristics unchanged.

A problem of generation of nonlinear unsteady waves on the surface of an ideal liquid in an infinitely deep fluid due to the motion of a submerged elliptic cylinder is considered. The initial formulation of the problem is reduced to an integrodifferential system of equations for the function defining the free surface shape and for the normal and tangential components of velocity on the free surface. The small-time asymptotics of the solution is constructed for the case of cylinder motion with a constant acceleration from the state at rest.

The behavior of an incompressible laminar boundary layer flow over a wedge in a nanofluid with suction or injection has been investigated. The model used for the nanofluid integrates the effects of the Brownian motion and thermophoresis parameters. The governing partial differential equations of this problem, subjected to their boundary conditions, are solved by the Runge–Kutta–Gill technique with the shooting method for finding the skin friction and the rate of heat and mass transfer. The result are presented in the form of velocity, temperature, and volume fraction profiles for different values of the suction/injection parameter, Brownian motion parameter, thermophoresis parameter, pressure gradient parameter, Prandtl number, and Lewis number. The conclusion is drawn that these parameters significantly affect the temperature and volume fraction profiles, but their influence on the velocity profile is comparatively smaller.

An unsteady boundary layer flow of a non-Newtonian fluid over a continuously stretching permeable surface in the presence of thermal radiation is investigated. The Maxwell fluid model is used to characterize the non-Newtonian fluid behavior. Similarity solutions for the transformed governing equations are obtained. The transformed boundary layer equations are then solved numerically by the shooting method. The flow features and heat transfer characteristics for different values of the governing parameters (unsteadiness parameter, Maxwell parameter, permeability parameter, suction/blowing parameter, thermal radiation parameter, and Prandtl number) are analyzed and discussed in detail.

In this paper, the (G'/G)-expansion method is used to obtain exact solitary-wave and periodic-wave solutions for nonlinear evolution equations arising in mathematical physics with the aid of symbolic computations, namely, the Klein–Gordon equation with quintic nonlinearity. Our work is motivated by the fact that the (G'/G)-expansion method provides not only more general forms of solutions, but also periodic and solitary waves. As a result, hyperbolic function solutions and trigonometric function solutions with parameters are obtained. The method is straightforward and concise, and its application is promising for other nonlinear evolution equations in mathematical physics.

The problem of motion of two “free” solid particles in a uniformly oscillating liquid is formulated and solved. In particular, it is found that the particles are capable of performing (side by side with oscillations) an average, monotonous displacement in the liquid as a whole.

Experiments were performed to study oil transport in the compound vortex produced by a uniformly rotating disk in a cylindrical container. It was found that on the liquid surface in the neighborhood of the axis of rotation, light oil formed a spot with spiral branches or broke up into separate elongated drops, and the spiral branches stretched out in the direction opposite to the direction of rotation of the liquid. In the bulk of the liquid in the vicinity of the axis of its rotation, oil formed a compact body. The geometric parameters of the structural components of the flows were determined.

Various conditions of formation of motionless closed hydrocarbon inclusions are considered: viscous instability of fluid displacement and inhomogeneous rock structure. Conditions of dynamic equilibrium of the inclusion in a water flow are given for one-dimensional and two-dimensional motion. Distributions of the oil content in inclusions of different shapes are numerically calculated. It is found that the amount of unrecovered oil depends on the ratio of the pressure gradients in the filtration flow of water pumped into the reservoir and the characteristic capillary pressure on the boundary of immiscible phases. It is demonstrated that the use of chemical reagents can substantially reduce the effect of capillary forces and promotes oil entrainment by the overall flow.

A mathematical model of relative permeability hysteresis in drainage and imbibition is constructed on the basis of percolation theory. It is shown that the results are in qualitatively agreement with experimental data.

A numerical simulation of the classical Stefan problem is performed in a modified formulation for a semitransparent gray medium. Temperature fields and the resulting radiation flux field are obtained, and the dynamics of displacement of the interface and the evolution of the temperature rise on the black left boundary of the sample for different values of the emissivity factor of the exposed right boundary are studied.

An analysis is carried out to study the unsteady two-dimensional Powell--Eyring flow and heat transfer to a laminar liquid film from a horizontal stretching surface in the presence of internal heat generation. The flow of a thin fluid film and subsequent heat transfer from the stretching surface is investigated with the aid of a similarity transformation. The transformation enables to reduce the unsteady boundary layer equations to a system of nonlinear ordinary differential equations. A numerical solution of the resulting nonlinear differential equations is found by using an efficient Chebyshev finite difference method. A comparison of numerical results is made with the earlier published results for limiting cases. The effects of the governing parameters on the flow and thermal fields are thoroughly examined and discussed.

With the use of different approaches and boundary conditions, the deformation of a long narrow rectangular membrane disposed within a rigid wedge matrix is simulated using different approaches and boundary conditions. The basic relations characterizing the stress–strain state of the membrane at different stages of deformation are obtained. The results of numerical experiments studying the characteristics of deformation of membranes are given.

This paper presents a mathematical model for the analysis of the stress–strain state of ice cover in the presence of a snow layer under dynamic loads. Numerical calculations were made using the model of indestructible ice, and the results were compared with experimental data.

The propagation of harmonic elastic wave in an infinite three-dimensional matrix containing an interacting low-rigidity disk-shaped inclusion and a crack. The problem is reduced to a~system of boundary integral equations for functions that characterize jumps of displacements on the inclusion and crack. The unknown functions are determined by numerical solution of the system of boundary integral equations. For the symmetric problem, graphs are given of the dynamic stress intensity factors in the vicinity of the circular inclusion and the crack on the wavenumber for different distances between them and different compliance parameters of the inclusion.

In this paper addressing how to predict structural reliability and based upon thorough research, the four most common types of load stresses are integrated into three related models, using Turkstra's rule. Predictions of the combined loads are calculated, both with and without strength degeneration, using Turkstra's method and the stress-strength interference theory. An illustration is provided, demonstrating that the predictive models are practical, feasible, and consistent with standard engineering practices.

In this paper, a numerical meshless method called the weakly compressible smoothed particle hydrodynamic (WCSPH) method, which is a two-dimensional model of a weakly compressible fluid, is applied to simulate the plunging wave breaking process. This model solves the viscous fluid equations to obtain the velocity and density fields and also solves the equation of state to obtain the pressure field. The WCSPH method is demonstrated to have a higher computational efficiency than the basic SPH model. To simulate the turbulent behavior of the fluid flow in the wave breaking procedure, a sub particle scale (SPS) model is used, which is obtained from the Large eddy simulation (LES) theory. To consider the accuracy of the standard WCSPH model (WCSPH model without considering the turbulent effect), a dam break test is performed, and model results are compared with available experimental data.

A possibility of degeneration of relationships between stresses and their derivatives with respect to the coordinates in the plane problem of the elasticity theory is considered. For particular dependences of the parameters of elasticity on coordinates, curves are given, for which degeneration conditions are satisfied. It is shown that even a small inhomogeneity of the medium causes stress instability.

A mathematical model of a circular disk-shaped brittle crack whose faces are acted upon by cohesive forces, whose magnitude depends on the distance between the faces. An algorithm of numerical solution of the singular nonlinear improper integral equation defining the crack profile was developed which can be used for other integral equations of this type. It is shown that taking into account the coupling forces between the crack faces leads to their gradual closing with distance from the center of the crack.

A laser optoacoustic method for analyzing the effect of porosity on the local isotropic Young's modulus of composite materials was proposed and experimentally implemented. Using as an example samples of a metal matrix composite based on silumin with reinforcing microparticles of silicon carbide, SiC, in various concentrations, it is shown that to provide an effective increase in Young's modulus with increasing concentration of SiC, the porosity of the final sample should not exceed 2%.

The wear of steel plates under the impact of a hydroabrasive jet was studied experimentally by varying the distance between the sample surface and the nozzle, the angle of impingement of the jet on the plate, and the abrasive concentrations in water and in the ambient medium (jet in air, submerged jet). The results are compared with available data on the structure of the jet and jet flow around an obstacle. It is shown that the addition of abrasive particles to the liquid can be used to study the liquid jet flow around an obstacle because the form of surface wear allows one to determine the region of impact of the jet core, the deceleration region, and the near-wall flow region before flow separation.

Results of experimental investigations of a multi-injector combustion chamber in the attached pipeline regime are presented. An IT-302M hotshot wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences is used as a source of a high-enthalpy gas (air). The tests are performed at Mach numbers of 3, 4, and 5 in the ranges of the total temperature from 2000 to 3000 K and static pressure from 0.08 to 0.23 MPa. The block of injectors is made in two variants: with different relative lengths of wedge-shaped injectors (cocurrent injection of hydrogen). The influence of the conditions at the combustor entrance on ignition and stable combustion of hydrogen is studied. Intense combustion of hydrogen is obtained only at Mach numbers of 3 and 4. The mechanism of the “two-stage” evolution of fuel combustion in the combustor is analyzed. The experimental data are analyzed and compared with numerical predictions.

A kinetic model of ignition and combustion of heavy n-alkenes n-C₁₀H ₂₂ and n-C₁₂H₂₆), benzene, and jet propellant Jet-A, hich is modeled by a BD surrogate consisting of n -decane 80%) and benzene (20%), is developed. The model is tested through comparisons with a large set of experimental data on the ignition delay time in both higher-temperature ( T > 1000 K) and low-temperature ( T = 650–950 K) regions and also on the behavior of species concentrations during benzene oxidation in a flow-type reactor and during benzene combustion in a special burner. Other reaction mechanisms developed for the description of combustion of various surrogates modeling kerosene are briefly analyzed. It is demonstrated that the proposed model ensures a more adequate description of the measured ignition delay times than other known kinetic models, especially in the low-temperature range ( T = 650–950 K). Specific features of the kinetics of low-temperature oxidation of the BD surrogate are analyzed.

This paper presents a physicomathematical model and results of numerical simulation of the initiation and propagation of detonation waves in shock tubes. A combustible mixture of hydrogen and oxygen diluted with argon is considered. A detailed structure of the flow in the shock tube is obtained by calculations. The calculated ignition delay was compared with experimental data.

Mathematical simulation of the propagation mechanisms of combustion waves and heterogeneous detonation in sharply expanding pipes was performed using the equations of two-dimensional axisymmetric unsteady motion of a reacting mixture of a gas and monofuel particles. The influence of the main determining parameters of the gas–particle mixture and the pipeline on the propagation of nonstationary detonation waves was studied. Dependences of the critical ratio of the pipe diameters of the composite pipeline on the relative mass content of monofuel particles of different sizes are given.

Calculated and experimental data on combustion and detonation in mixtures where oxygen or air is used as an oxidizer and methane or coal dust is used as a fuel are presented.

Regimes of continuous detonation burning of synthesis gas–air mixtures in transverse (spinning) detonation waves are obtained for the first time in an annular cylindrical flow-type combustor. Carbon oxide–hydrogen mixtures with volume proportions of [CO]/[H₂] = 1/1, 1/2, and 1/3 are studied in a wide range of fuel-to-air equivalence ratios. The maximum detonation wave velocity equal to 1.57 km/s is observed for the mixture of CO + 3H₂ + air with a moderate (about 15%) excess of the fuel. The limits of existence of continuous detonation in terms of the equivalence ratio and the minimum specific flow rate of the mixture are determined. The range of detonation regimes obtained is constructed in the coordinates of the equivalence ratio–specific flow rate of the mixture.

A semi-empirical model of molecular dynamics is proposed within the molecular dynamics approach. The model is verified against the experimental dependence of the melting temperature of aluminum nanoparticles on their size. The specific heat of the particle and the phase transition heat are determined as functions of the initial size and temperature of the particle. It is demonstrated that these dependences tend to the limiting dependences, which describe the particle size in the volume phase, as the particle size increases. A comparison of the aluminum nanoparticle melting characteristics alculated by the model of molecular dynamics and by the phenomenological model reveals reasonable agreement in terms of the melting time.

The authors have found relationship between stress state and surface roughness of main fracture in rocks: with growth of maximum normal stress in the area of fracture, surface roughness of the maximum normal stress site decreases. Based on the found relationship, the authors propose a method of estimating stress state of a material by value of the material fracture surface roughness.

Under analysis is travel of P-waves in an elastic pipe partly buried in soil with dry friction. The mathematical formulation of the problem on impact pipe driving in soil is based on the model of axial vibration of an elastic bar, considering lateral resistance described using the law of solid dry friction. The author solves problems on axial load on pipe in interaction with external elastic medium, and compares the analytical and numerical results obtained with and without accounting for the external medium deformabilit.

Aimed to improve capacity of vibro-percussion driving of steel pipes in soil, the authors describe experimental modeling of the process with additional vibration exciters of axial and transverse vibrations series-linked to impulsive load source. Workability of combination of two extended action spectrum percussion units as the vibration exciter is illustrated.

The authors study work process of pneumatic percussion units with valveless air distribution under exhaust back pressure in drilled solid removal in long horizontal hole drilling machines. It is shown that range of efficient values of the machine performance equal to maximum percussion force does not change under increase in the exhaust back pressure.

The mathematical model of positive-displacement two-way hydropercussion system includes characteristics of the system design features and their interaction with rock mass. The author analyzes numerically their influence on dynamics and integral output capability of limit cycles.

The authors show three methods of energy saving in mine ventilation: recirculating airing, minimization of main mine fan pressure by privative adjustment, and two-parameter optimization of fan performance (by rotary velocity and angle of blades). Energy conservation in using any of the methods is proved in calculations.

The presented geoinformation system is based on cloud service classification of natural and mining-induced seismic events. The data entropy-based models treat seismic signals as functions of a “waveguide” led from the seismic source to the seismic station. The quality similarity or distinction of the models is related with the genesis of seismic events. The service includes Google App Engine cloud calculating technologies, IRIS Data Management Center web-services and local seismic monitoring databases. The application of the cloud service to classifying unknown-genesis seismic events is illustrated by the examples.

Using X-ray photoelectron spectroscopy, the authors analyze the change in the surface layer composition and chemical state of atoms of chalcopyrite and sphalerite as a result of treatment by high-power nanosecond electromagnetic impulses. General regular patterns and distinctions of modification of the mineral surface and flotability under energy impulse treatment are found. The research findings are supported by the results of experimental improvement gained in selective separation of sulfides after high-power nanosecond electromagnetic treatment.

The article considers principles of constructing kinetic models of a sorptive collector layer forming at sulfide mineral surface and explains the physics of the models that consists in the connection between ions of flotation slurry liquid phase and relative fractions of mineral grain surface .

Parameters of heterogeneous machining media in magnetic-gravity, gravity and flotation machines are studied using methods of computational fluid dynamics. Numerical modeling of separation processes allowed graphical and numerical characterization of separation. The article bases suggestions on improved designs of the gravity and magnetic-gravity processing equipment and offers approach to evaluating surface energy of mineral particles in flotation modeling.

Based on analyzed redistribution of nonferrous and precious metals in aqueous and weak acid solutions passed through copper–nickel ore dressing refuses, the authors have obtained distribution of the metals in mineral phases for different levels of filtering layer in the tailings and for different contact solutions. Potential extractability of gold and platinum at 28.4 and 3.9% of the total quantity of mine refuse, respectively, using weak acid contact solution is shown in the article.