Investigation of high-speed combustible gas ignited by a hot gas jetproduced in the shock tube

The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “line-flame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90m/s and the delay time of ignition is estimated in the range of 0.12–0.29ms. PACS 47.40.Nm; 82.40.FpPart of this paper was presented at the 5th International Workshop on Shock/Vortex Interaction, Kaohsiung, October 27–31, 2003.     

Direct numerical simulation of a liquid sheet in a compressible gas stream in axisymmetric and planar configurations

A thin liquid sheet present in the shear layer of a compressible gas jet is investigated using an Eulerian approach with mixed-fluid treatment for the governing equations describing the gas–liquid two-phase flow system, where the gas is treated as fully compressible and the liquid as incompressible. The effects of different topological configurations, surface tension, gas pressure and liquid sheet thickness on the flow development of the gas–liquid two-phase flow system have been examined by direct solution of the compressible Navier–Stokes equations using highly accurate numerical schemes. The interface dynamics are captured using volume of fluid and continuum surface force models. The simulations show that the dispersion of the liquid sheet is dominated by vortical structures formed at the jet shear layer due to the Kelvin–Helmholtz instability. The axisymmetric case is less vortical than its planar counterpart that exhibits formation of larger vortical structures and larger liquid dispersion. It has been identified that the vorticity development and the liquid dispersion in a planar configuration are increased at the absence of surface tension, which when present, tends to oppose the development of the Kelvin–Helmholtz instability. An opposite trend was observed for an axisymmetric configuration where surface tension tends to promote the development of vorticity. An increase in vorticity development and liquid dispersion was observed for increased liquid sheet thickness, while a decreasing trend was observed for higher gas pressure. Therefore surface tension, liquid sheet thickness and gas pressure factors all affect the flow vorticity which consequently affects the dispersion of the liquid.      

Startup analysis of oil-fired furnace – the smoothing Monte Carlo model approach

 A multi-dimensional mathematical thermal model of the oil-fired furnace has been developed. Radiation calculation of this model is based on the Hottel's zone method incorporating with the statistical Monte Carlo method to determine the total exchange areas. The whole furnace is divided into 4 gaseous zones and 18 surface zones. The Monte Carlo method integrated with the least square smoothing technique considering both conservation and reciprocity is used to evaluate the total exchange areas, i.e. surface–surface, surface–gas, gas–gas and gas–surface, directly for both the absorbing and emitting media. A better accuracy is achieved in the determination of the total exchange areas by using the proposed smoothing Monte Carlo method. Received on 10 April 2000     

Possibility of reaching higher contents of a gas in a liquid using shock waves

The effect of shock waves on gas absorption by liquid in bubbly media with different degrees of gas solubility is studied. It is shown that a shock wave acting on a gas-liquid medium can significantly enhance the mass transfer between the gas and the liquid. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 64–70, March–April, 2000.     

Formation of a gas hydrate due to injection of a cold gas into a porous reservoir partly saturated by water

Specific features of formation of gas hydrates due to injection of a gas into a porous medium initially filled by a gas and water are considered. Self-similar solutions of an axisymmetric problem, which describe the distributions of the basic parameters in the reservoir, are constructed. The existence of solutions is demonstrated, which predict gas hydrate formation both on the frontal surface and in the volume zone. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 137–150, May–June, 2008.     

Linearized Burnett Equation for the Dynamic Pressure of a Relativistic Gas

The linearized Burnett equation for the dynamic pressure of a relativistic gas of hadrons is calculated from a relativistic kinetic theory. It is shown, as in a previous paper [1], that the coefficient of the term with a non-homogeneous temperature field, – the heating term – is bigger than the one with the divergence of the four-velocity, – the bulk viscosity term.     

Mathematical treatment of the discharge of a laminar hot gas in a stagnant colder atmosphere

We study the boundary-layer approximation of the classical mathematical model that describes the discharge of a laminar hot gas in a stagnant colder atmosphere of the same gas. We prove the existence and uniqueness of solutions to a nondegenerate problem (without zones of stagnation of gas temperature or velocity). The asymptotic behavior of these solutions is also studied __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 4, pp. 192–205, July–August, 2008.     

Reflection of pressure waves of moderate intensity at a solid wall in a liquid with bubbles of a readily soluble gas

The present paper is concerned with an experimental study of the process of gas dissolution behind a shock wave in a liquid with bubbles of a readily soluble gas, the influence of gas dissolution on the wave evolution, and strengthening of the shock wave after reflection from a solid wall. Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 5, pp. 19–24, September–October, 1998.     

Resonant oscillations of a gas in an open-ended tube in a weak turbulence regime

An analytical theory of resonant oscillations of a gas in an open-ended tube is developed. The gas flow in the tube is assumed to be turbulent. A model of gas flow near the open end of the tube is constructed. This model allows a boundary condition that is free of empirical parameters to be obtained. Theoretical results are in reasonable agreement with experimental data obtained by other authors. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 92–99, May–June, 1998.     

Explicit Rate–Time Solutions for Modeling Matrix–Fracture Flow of Single Phase Gas in Dual-Porosity Media

One of the widely used methods for modeling matrix–fracture fluid exchange in naturally fractured reservoirs is dual porosity approach. In this type of modeling, matrix blocks are regarded as sources/sinks in the fracture network medium. The rate of fluid transfer from matrix blocks into fracture medium may be modeled using shape factor concept (Warren and Root, SPEJ 3:245–255, 1963); or the rate–time solution is directly derived for the specific matrix geometry (de Swaan, SPEJ 16:117–122, 1976). Numerous works have been conducted to study matrix–fracture fluid exchange for slightly compressible fluids (e.g. oil). However, little attention has been taken to systems containing gas (compressible fluid). The objective of this work is to develop explicit rate–time solutions for matrix–fracture fluid transfer in systems containing single phase gas. For this purpose, the governing equation describing flow of gas from matrix block into fracture system is linearized using pseudopressure and pseudotime functions. Then, the governing equation is solved under specific boundary conditions to obtain an implicit relation between rate and time. Since rate calculations using such an implicit relation need iterations, which may be computationally inconvenient, an explicit rate–time relation is developed with the aid of material balance equation and several specific assumptions. Also, expressions are derived for average pseudopressure in matrix block. Furthermore, simplified solutions (originated from the complex general solutions) are introduced applicable in infinite and finite acting flow periods in matrix. Based on the derived solutions, expressions are developed for shape factor. An important observation is that the shape factor for gas systems is the same as that of oil bearing matrix blocks. Subsequently, a multiplier is introduced which relates rate to matrix pressure instead of matrix pseudopressure. Finally, the introduced equations are verified using a numerical simulator.     

Optimization of shock-wave action on a spherical bubble in an ideal incompressible liquid

The possibility of controlling the oscillations of a spherical gas bubble in an ideal incompressible liquid is subjected to theoretical analysis. Liquid surface tension forces are not taken into account. The optimization process realizing a maximum of the radius amplitude and a maximum of the gas pressure in the bubble for a given impulsive change of pressure at infinity is considered. A shock-resonance bubble oscillation procedure giving stepwise pressure changes at the extrema of the radius is constructed. This problem is of interest in connection with the investigation of cavitation erosion [1] and processes in biological tissues [2–4]. Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 175–178, September–October, 1988.     

Transformation of energy and composition of gas mixtures in a collision of rarefied supersonic flows

Transformation of energy and composition of gas mixtures in a convergent flow from a strip source on a cylindrical surface toward the axis is systematically studied with the use of the direct simulation Monte Carlo method. Information on the influence of gas-flow rarefaction and system geometry on the temperature and concentration of the heavy gas in a dense cloud formed on the axis is obtained. The use of convergent supersonic flows is demonstrated to offer new possibilities for research in the field of physical gas dynamics. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 198–204, March–April, 2009     

Unsteady filtration of a gas

The unsteady filtering flow of a gas described by the equations of motion proposed by Khristianovich in [1] is investigated. It is shown that for the gas flow in the pores a critical regime can develop when the reduced velocity (an analog of the Mach number in gas dynamics) is less than unity. The reduced velocity is the ratio of the flow velocity to the velocity of propagation of small filtering perturbations at a given point of the flow. St Petersburg. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 201–203, January–February, 1994.     

Visualizing near-surface concentration fluctuations using laser-induced fluorescence

A method for observing near-surface fluctuations in pH caused by a water–air flux of carbon dioxide under conditions of ambient atmospheric carbon dioxide levels is developed and tested. Peaks in fluorescence intensity measured as a function of pH and turbulence are shown to be consistent with predictions from a chemical kinetics model of CO₂ exchange. The square root of the frequency of the pH fluctuations scale linearly with independently measured bulk air–water gas transfer velocities in agreement with surface divergence models for air–water gas transfer. These data indicate that the method proposed here is tracking changes in near-surface CO₂ concentrations. This laser-induced fluorescence method can be used to study the air–water exchange of CO₂ in wind-wave tunnels without the need for elevated CO₂ concentrations in the gas phase.     

Measurement of gas transfer across wind-forced wavy air–water interfaces using laser-induced fluorescence

Optical distortions have previously prevented non-intrusive measurements of dissolved oxygen concentration profiles by Laser induced fluorescence (LIF) to within 200 μm of the air–water interface. It is shown that by careful experimental design, reliable measurements can be obtained within 28 μm of moving air–water interfaces. Consideration of previously unidentified optical distortions in LIF imagery due to non-linear effects is presented that is critical for robust LIF data processing and experimental design. Phase resolved gas flux measurements have now been accomplished along wind forced microscale waves and indicate that the highest mean gas fluxes are located in the wave troughs. The local mean oxygen fluxes as determined by LIF techniques can be reconciled to within 40% of those obtained by bulk measurement in the water. These data provide a new perspective on wind-wave enhancement of low solubility gas transfer across the air–water interface.     

Existence of solutions of Kraiko's problem

Three initial-boundary-value problems for the equations of gas dynamics are formulated. Successive solution of these problems yields a solution of Kraiko's problem of the isentropic transition of an ideal gas from a homogeneous state of rest to another state of rest with higher or lower density. Solutions are constructed for plane, cylindrical, and spherical layers of an ideal gas. The existence of locally analytic solutions is proved. Ural State Academy of Service, Ekaterinburg 620034. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 3, pp. 48–55, May–June, 2000.     

Thermohydrodynamics of continuous-wave CO2 lasers with a closed cycle of the flow

The problem of pressure losses upon gas motion along a closed circuit containing channels in which heat is supplied to and removed from the gas is studied. The object where the pressure losses are studied is a CO₂ laser with a crossflow. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, 630090 Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 1, pp. 3–13, January–February, 2000.     

Effect of vapor condensation on forced convection heat transfer of moistened gas

The forced convection heat transfer with water vapor condensation is studied both theoretically and experimentally when wet flue gas passes downwards through a bank of horizontal tubes. Extraordinarily, discussions are concentrated on the effect of water vapor condensation on forced convection heat transfer. In the experiments, the air–steam mixture is used to simulate the flue gas of a natural gas fired boiler, and the vapor mass fraction ranges from 3.2 to 12.8%. By theoretical analysis, a new dimensionless number defined as augmentation factor is derived to account for the effect of condensation of relatively small amount of water vapor on convection heat transfer, and a consequent correlation is proposed based on the experimental data to describe the combined convection–condensation heat transfer. Good agreement can be found between the values of the Nusselt number obtained from the experiments and calculated by the correlation. The maximum deviation is within ±6%. The experimental results also shows that the convection–condensation heat transfer coefficient increases with Reynolds number and bulk vapor mass fraction, and is 1∼3.5 times that of the forced convection without condensation.     

Description of the anomalous Rayleigh-Taylor instability on the basis of the model of dynamics of a three-velocity three-temperature mixture

A problem of evolution of the Rayleigh-Taylor instability on a sinusoidally perturbed interface in the field of artificial gravity is studied on the basis of the model of a three-velocity three-temperature mixture of gases. If the upper part of the mixture consists of the light and heavy gases (the heavy gas is heavier than the pure gas at the bottom, but the mixture as a whole is lighter than the pure gas), it is demonstrated that the growth of perturbations with formation of mixture jets penetrating into the pure gas is observed in a certain range of concentrations of the heavy gas. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 58–67, January–february, 2009.     

On the transient regime in nonstationary supersonic flow past a body

The transient regime in gas flow past a stepwise accelerated body is analyzed by the method of singular perturbations at small Froude numbers. A marked effect of the initial conditions on the shock layer gas flow is demonstrated. The problem of flow past a wedge is solved in quadratures. St.Petersburg. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 111–121, January–February, 1997.