Mathematical theory of the stationary propagation velocity of a fine-scale turbulent flame

A boundary-value problem in the theory of propagation of a fine-scale turbulent flame is investigated, taking into account the influence of temperature and concentration pulsations on the magnitude of the heat liberation rate. In contrast to [1], the case when a second-order reaction proceeds in the flame is examined in detail. Conditions are found for the existence of a turbulent flame; the structure of the flame front is studied by a computational method. A change in the progress of the reaction is disclosed near the propagation limits.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 109–114, July–August, 1973.     

Nonsteady burning of a solid propellant in a gaseous oxidizer flow

The burning of a solid propellant is investigated for nonsteady heat propagation in the induction zone. The equation of heat conduction in the propellant is solved in finite form for the case of a sharp change in burning rate; the time dependence of the temperature gradient at the propellant surface is obtained and used to investigate the mechanism of collapse of the diffusion flame above the surface. The combustion stability of a propellant burning in a channel with a large free volume is analyzed. The perturbations of the gas-dynamic quantities are related with the perturbations of the burning rate and hence with the properties of the induction zone in the solid phase. An analysis of the dispersion relation for the limiting case of propagation of acoustic waves in a stationary gas shows that the longitudinal acoustic perturbations that develop in the channel may grow with time, interacting with the heated subsurface layer of propellant.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fizikt, No. 4, pp. 44–52, July–August, 1971.In conclusion the author thanks B. V. Librovich for formulating and discussing the problem and A. G. Istratov and V. G. Markov for their valuable comments.     

Theory of flame propagation in a gas and drop mixture

The equations of a reacting multiphase continuous medium [1] are used to investigate the problem of steady-state flame front propagation in a gas mixture with evaporating drops. A simple model for ignition of the liquid drops is proposed which is based on the application of the method of equally accessible surfaces [2] to the heat and mass exchange processes between the microflames surrounding the separate drops, the drops, and the carrying gas medium. The parameter distributions in the macroscopic flame front as well as the dependences of the flame propagation velocity in the gas suspension on a number of parameters governing the process under investigation are represented.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 101–108, July–August, 1973.     

Propagation rate and limits of existence of a turbulent flame

In a theoretical study of turbulent burning it is usually assumed that the average rate of the chemical reaction (heat release) is determined only by the average temperature. Ya. B. Zel'dovich [1] and later T. Karman [2] noted the necessity of taking into account the effect of temperature pulsations on the reaction rate. A quantitative estimate of this effect on the reaction rate constant is given in [3]. A critical analysis of various approaches to the theoretical study of turbulent flames is given in the reviews [4, 5]. In the present article, it is shown that, taking the pulsation component of the temperature and concentration into account, the average rate of the chemical reaction depends on the gradient of the mean temperature and the scale of the turbulent pulsations. The case, where a first-order reaction takes place in the flame is studied in detail. Existence and uniqueness theorems which determine the limits of the propagation of flames are proven. Quantitative rules for the propagation rate, limit, and structure of a turbulent flame front are analyzed with respect to the results of a numerical calculation of a series of variants. Dimensional interpolation equations are presented for the total propagation rate of a flame.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 65–76, May–June, 1972.     

The Wavelet-Based Technique in Dispersive Wave Propagation

The paper expounds a wavelet-based technique. The techniques is applied to the dispersive wave equation by describing wave propagation by a composition of fundamental (harmonic) wavelets. The linear Klein–Gordon equation is analyzed and associated approximate wavelet solutions are considered for fixed resolution levels. Discretized wavelet families are computed explicitly using a basis of time harmonic wavelets. Some applications at various low resolution levels show that the technique proposed provides new opportunities for wave propagation analysis     

Nonlinear waves in a viscous compressible fluid with relaxation

The propagation and stability of nonlinear waves in a viscous compressible fluid with relaxation that satisfies a Theological equation of state of Oldroyd type are investigated. An equation that describes the structure of the wave perturbations and its evolution is derived subject to the condition of balance of the nonlinear dissipative and relaxation effects, and its solutions of the solitary wave type are analyzed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 31–35, May–June, 1993.     

On the theory of solitons in systems with dissipation

In the weakly nonlinear approximation wave processes in flowing films, the propagation of concentration waves in chemical reactions, the hydrodynamic instability of a laminar flame, and thermocapillary convection in a thin layer are described by equations of the type h_t + 4hh_x + h_xx + h_xxxx=0. A special role in wave processes is played by nonlinear localized signals-solitary waves or solitons. In this paper the methods of the theory of dynamical systems are used to carry out a full investigation of solutions of the stationary soliton type for the above-mentioned equation.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 91–97, May–June, 1986.     

Propagation of shear perturbations in dilatant liquids

Processes of shear-perturbation propagation in dilatant liquids are investigated. The evolution over time of the carrier of the Cauchy-problem solution for the quasilinear parabolic equation describing such processes is analyzed. Nonlinear effects of finite velocity and spatial localization of the shear perturbations are discussed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 60–65, November–December, 1978.     

Quasilongitudinal propagation of narrow beams of nonlinear magnetohydrodynamic waves

An equation, analogous to the Khokhlov-Zabolotskaya equation, is derived for narrow beams of quasitransverse waves propagating at small angles to a magnetic field. The effect of diffraction on wave propagation is investigated in the linear approximation.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 21–28, July–August, 1986.     

The detonation burning of a fuel mixture resulting from a double explosion

A study is made of the propagation of a multifront detonation burning in a fuel mixture consisting of a gaseous fuel and an oxidant with additions of combustible solid or liquid particles arising as a result of a double point explosion. In such combustible media it is possible for there to be propagation of several detonation or burning fronts following one after the other. The easily igniting gaseous fuel burns in the first detonation wave, which propagates in the gaseous mixture with particles which are heated by the products of the explosion, ignite and burn in the second detonation wave or in the flame front. Self-similar regimes of propagation of such waves in an idealized formulation were studied in [1].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 126–131, March–April, 1985.     

Propagation of nonlinear waves in a porous medium with two-phase saturation by a liquid and a gas

The propagation of nonlinear waves through a porous medium saturated with a viscous liquid and a gas is investigated with allowance for the capillary pressure. Numerical solutions of the traveling-wave type are constructed for the generalized Korteweg-de Vries-Burgers equation for the wave amplitudes. Three types of regimes of longitudinal wave propagation, including soliton-like regimes, are found.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 86–95, July–August, 1996.     

Flow of a free jet of rheologically complex fluid from a vibrating capillary

The propagation of finite-amplitude waves along a vibrating capillary jet is studied. The standing wave equation is derived.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 3–10, May–June, 1985.     

On the propagation of pressure waves in saturated porous media

The problem of the propagation of pressure waves through compressible porous media saturated with a slightly compressible fluid is considered. By using Darcy's law the problem is reduced to a mixed initial-boundary value problem for an equation of the heat conduction type with a nonlinear term. The method of quasi-characteristics is used to solve this equation numerically. Solutions of the wave propagation problem for media with different permeability coefficients are presented. A solution of the inverse problem of determining the permeability coefficient using wave-pulse test data is constructed on the basis of a set of solutions of the direct problem.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 81–84, November–December, 1996.     

Propagation of nonlinear Alfvén surface waves along a tangential magnetohydrodynamic discontinuity in an incompressible fluid

The paper considers the propagation of low-amplitude nonlinear waves over a surface of magnetic discontinuity. An equation for these waves is derived. The evolution of a sinusoidal perturbation is investigated. The discontinuity formation time is numerically determined.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 98–105, January–February, 1985.     

An investigation of one third-order equation not allowed with respect to the time derivative

This paper is devoted to an investigation of the equation ut+u_x+uu_x =u_xxt+u_xx, which is a model equation for the problem of the nonsteady filtration of two immiscible liquids. A combined problem on all axes is set up for this equation: The initial condition u(0, x) and the boundary conditions at infinity are assigned. A solution of the special form u₀(x – ct), whose propagation velocity c is determined from the boundary conditions, is analyzed. The stability of this solution in a linear approximation is demonstrated in a certain particular case.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 96–103, November–December, 1978.In conclusion, the author thanks G. I. Barenblatt for constant attention to the present work.     

Asymptotic solution of the Orr-Sommerfeld equation in the outer region of the boundary layer with allowance for nonparallelism

There have been many publications devoted to the investigation of the hydrodynamic stability of nonparallel flows on the basis of the modified Orr-Sommerfeld equation [1–4]. Taking into account the additional terms associated with the presence in the flow of a transverse component of velocity and acceleration can lead not only to a significant quantitative discrepancy as compared with calculations based on the usual Orr-Sommer-feld equation but also to qualitatively new results (nonclosure of the neutral curves for flow on a permeable surface in the presence of strong injection [4]). In this paper an asymptotic solution of the Orr-Sommer-feld equation, valid in the outer region of boundary layer flow, is constructed for self-similar gradient flow over a surface (Falkner-Skan flow). The continuity of the eigenvalue spectrum for an unbounded increase in the perturbation propagation velocity is demonstrated on the basis of the solution obtained. For the ordinary Orr-Sommerfeld equation a continuous transition of the spectrum through the value of the perturbation propagation velocity C_r=1 (which coincides with the velocity of the external flow) is impossible [5].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 171–173, January–February, 1987.     

Stationary modes of combustion in a fine-scale turbulent stream

The majority of models of the turbulent combustion of gases are based mainly on intuitive concepts concerning the processes occurring in the flame. The characteristics of a turbulent flame are estimated from considerations of dimensionality and similarity. A detailed review of works on turbulent combustion is given in [1]. Problems on the calculation of the combustion rate in a turbulent stream as a proper value of the equations of heat and mass transfer and of the corresponding boundary conditions have recently been raised. Here too one must rest on assumptions of a semiempirical nature, which in large measure is connected with the inadequate level of development of turbulence theory. In the present work the equation of propagation of the zone of chemical reactions in the stream is averaged statistically by analogy with studies of turbulent flows. Correct averaging is possible at scales of hydrodynamic disturbances smaller than the flame thickness (fine-scale turbulence). The temperature pulsations are related with the size of the heat flux using the theory of mixing lengths. The main influence is specific to effects arising during averaging of the heat release function. Two stationary modes, distinguished by the normal propagation velocity ₁, are isolated within the framework of the Cauchy problem with a given initial mixture temperature and zero heat flux in the burned gas. A heat conduction mode occurs with a stream velocity > ₁ and an induction mode with < ₁. An expression is found for ₁ which reflects the principal effects in the flame and which in the limit coincides with the equation of Zel'dovich and Frank-Kamenetskii for a laminar flame. In those cases when the distorting effect of the heat release function is small, the turbulence affects the combustion rate through mechanisms of intensification of transport processes.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 118–124, September–October, 1973.     

Detonation Wave Propagation in Rotational Gas Flows

This paper studies the propagation of detonation and shock waves in vortex gas flows, in which the initial pressure, density, and velocity are generally functions of the coordinate — the distance from the symmetry axis. Rotational axisymmetric flow having a transverse velocity component in addition to a nonuniform longitudinal velocity is considered. The possibility of propagation of Chapman–Jouguet detonation waves in rotating flows is analyzed. A necessary conditions for the existence of a Chapman–Jouguet wave is obtained.     

Crack trajectory instability: Propagation in inhomogeneous medium

The problem of crack trajectory stabilization in composite material is investigated. The equation for a crack path is found from the variational principle. It is considered as a path along which the extreme amount of energy is generated during the destruction. This statement corresponds to the variational problem analogous to the Lagrange–d’Alembert principle of classic mechanics and to the Fermat principle in optic and acoustic. For a crack path in inhomogeneous medium, nonlinear differential equation is obtained. Stability of the crack propagation in the inhomogeneous medium is considered. In particular, a 2D crack propagating in a composite material is considered. The path of propagation is assumed to cross layers or fibres. For layered and piece-wise continuous composites, the resulting governing equation corresponds to different kind of Duffing’s equation. The bifurcations of the trajectory and instability of crack path are investigated numerically. Conditions of crack trajectory stabilization are found. Properties of the materials that stabilized the crack trajectory are found.     

Self-similar problems of propagation of an extended hydrofracture in a permeable medium

The propagation of an extended hydrofracture in a permeable elastic medium under the influence of an injected viscous fluid is considered within the framework of the model proposed in [1, 2]. It is assumed that the motion of the fluid in the fracture is turbulent. The flow of the fluid in the porous medium is described by the filtration equation. In the quasisteady approximation and for locally one-dimensional leakage [3] new self-similarity solutions of the problem of the hydraulic fracture of a permeable reservoir with an exponential self-similar variable are obtained for plane and axial symmetry. The solution of this two-dimensional evolution problem is reduced to the integration of a one-dimensional integral equation. The asymptotic behavior of the solution near the well and the tip of the fracture is analyzed. The difficulties of using the quasisteady approximation for solving problems of the hydraulic fracture of permeable reservoirs are discussed. Other similarity solutions of the problem of the propagation of plane hydrofractures in the locally one-dimensional leakage approximation were considered in [3, 4] and for leakage constant along the surface of the fracture in [5–7].Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 91–101, March–April, 1992.