Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2016 number 6

The problem of initiation and stabilization of detonation combustion of a hydrogen-air mixture injected into an axisymmetric channel with a finite-length central body in a flow with a Mach number M₀=5-9 is solved. It is numerically demonstrated that the presence of the central body both in a convergent-divergent nozzle and in an expanding channel leads to stabilization of detonation combustion of a stoichiometric hydrogen-air mixture at free-stream Mach numbers M₀>7. Various channel configurations that ensure different values of thrust generated by detonation combustion of a stoichiometric hydrogen-air mixture are compared.

The existence of axiradial acoustic resonance oscillations of the main air flow in bypass channels of aviation engines is demonstrated theoretically and experimentally. Numerical and analytical methods are used to determine the frequency of the acoustic resonance oscillations for the lowest modes of open and closed bypass channels of the PS-90A engine. Experimental investigations reveal new acoustic resonance phenomena arising in the air flow in the cavities of the bypass channels in the main duct of this engine owing to instability of the main air flow. The results of numerical, analytical, and experimental studies of the resonance frequencies reached in the flow in the bypass cavities in the main duct of the PS-90A engine are found to be in reasonable agreement. As a result, the types of the resonance oscillations in the bypass channels can be accurately described.

The example of two non-stationary forces is used to study the impact of external influences leading to the occurrence of additional ponderomotive forces on the wave modes of the film freely flowing down a vertical surface. In the first case, the ferromagnetic fluid film is affected by the electric field. For the given forces, in the case of small flow rates, the problem is reduced to the solution of a model equation for the perturbation of the film thickness. The numerical solutions of the problem are obtained, and several characteristic scenarios of evolution of periodical perturbations are considered. It is shown that changes in the boundaries of the region of linear stability of the unperturbed flow with a flat free surface under the influence of ponderomotive forces has a great impact on the flow.

The dynamic behavior of the magma melt saturated with a strongly compressed gas at a high temperature, which is located between two rigid boundaries aligned symmetrically with respect to the vertical axis, is considered. A constant pressure is maintained at the channel bottom, while the pressure in the medium is initially distributed in accordance with the hydrostatic law. The top of the channel is hermetically sealed with a plug, which is affected by a constant pressure equal to the atmospheric value. The state of the melt after instantaneous removal of the plug is studied.

The problem of gas pressure equalization in a porous medium filling a tube with a closed end upon impact is solved.In this case, the initial filtration velocity behind the shock wave should be specified as initial data, in addition to the impact pressure.It is shown that the pressure surge decays at a finite distance and pressure equalization occurs in a finite time. Approximate submodels of discontinuous and smooth solutions are obtained.

An analytical study of the entropy generation rate and heat transfer in a flow of immiscible couple stress fluids between two horizontal parallel plates under a constant pressure gradient is performed. Both plates are kept at different and constant temperatures higher than that of the fluid. The Stokes couple stress flow model is employed. The classical no-slip condition is prescribed at the plates, and continuity of the velocity, rotation, couple stress, shear stress, temperature, and heat flux is imposed at the interfaces. The velocity and temperature distributions are found analytically, and they are used to compute the entropy generation number and Bejan number. The effects of the couple stress parameter and Reynolds number on the velocity, temperature, entropy generation number, and Bejan number are investigated. It is observed that the friction near the plates in couple stress fluids decreases as the couple stress increases.

Forced oscillations of a cylindrical drop of an inviscid liquid surrounded by another liquid and bounded in the axial direction by rigid planes are investigated.The system is affected by vibrations whose force is directed parallel to the axis of symmetry of the drop. The speed of motion of the contact line is proportional to the deviation of the contact angle from the value at which the drop is in equilibrium. Linear and nonlinear oscillations are considered. The conditions of the occurrence of resonance are determined.

The self-gravitating instability of the present model is discussed by using a simple linear theory. The problem is formulated for a rotating fluid layer, and a dispersion relation valid for all kinds of perturbations is derived and discussed. The self-gravitating force is found to be a destabilizing factor for a small range of wavenumbers, while it is stabilizing in other ranges, depending on the density ratio of the fluids. For high values of the angular velocity, the rotational force produces a stabilizing effect and can suppress the self-gravitating instability. In the absence of the self-gravitating force, the model of a rotating fluid layer is marginally stable

A flow past a heterogeneous porous sphere is investigated by using the perturbation theory. The flow through the sphere is divided into two zones, which are fully saturated with the viscous fluid, and the flow in these zones is governed by the Brinkman equation. The space outside the sphere, where a clear fluid flows, is also divided into two zones: the Navier-Stokes zone and the Oseen flow zone. The solutions on the interface inside the sphere are matched with the condition proposed by Merrikh and Mohammad. The stream function in the Navier-Stokes zone is matched with that on the sphere surface by the condition proposed by Ochoa-Tapia and Whitaker. It is found that the drag on the spherical shell decreases as the permeability toward the sphere boundary increases.

A similarity solution for a steady laminar mixed convection boundary layer flow of a nanofluid near the stagnation point on a vertical permeable plate with a magnetic field and a buoyancy force is obtained by solving a system of nonlinear ordinary differential equations. These equations are solved analytically by using a new kind of a powerful analytic technique for nonlinear problems, namely, the homotopy analysis method (HAM). Three different types of nanoparticles, namely, copper Cu, alumina Al₂O₃, and titanium oxide TiO₂, with water as the base fluid are considered. The influence of the volume fraction of nanoparticles, permeability parameter, magnetic parameter, and mixed convection parameter on the surface shear stress and surface heat transfer, as well as on the velocity and temperature profiles, is considered. It is observed that the skin friction coefficient and the local Nusselt number increase with the nanoparticle volume fraction for all types of nanoparticles considered in this study. The greatest values of the skin friction coefficient and the local Nusselt number are obtained for Cu nanoparticles.

Schlieren visualization is used to study the generation of Mach waves and impact noise in a wide range of frequencies by single supersonic jets and by groups of jets in the Mach number range M=1-4.

A two-dimensional magnetohydrodynamic boundary layer flow of the Eyring-Powell fluid on a stretching surface in the presence of thermal radiation and Joule heating is analyzed. The Soret and Dufour effects are taken into account. Partial differential equations are reduced to a system of ordinary differential equations, and series solutions of the resulting system are derived. Velocity, temperature, and concentration profiles are obtained. The skin friction coefficient and the local Nusselt and Sherwood numbers are computed and analyzed.

Two problems on flat damping surface waves in an inhomogeneous medium are under consideration: the problem of propagation of the waves similar to the Rayleigh waves in an isotropic elastic half-space bordering with the layer of an ideal incompressible fluid, and the problem of propagation of the waves to the Love waves in a semi-infinite saturated porous medium bordering with the layer of an isotropic elastic medium.

The flow around a stationary process sphere by an accelerating flow of a pseudoplastic fluid at Reynolds numbers Re = 0-200 and dimensionless acceleration Ga = 10-10⁴ is studied by numerical simulation. It is shown that the analytical expression of the force of the added mass for an ideal fluid is appropriate for a pseudoplastic fluid. An expression for calculating the hereditary force of the type of the Basset force for a pseudoplastic fluid is proposed.

The plane consolidation problem for elastic half-space under an instantaneously applied vertical load is solved in the general case assuming that the following Terzaghi hypothesis holds.

A mathematical model is proposed to describe the substitution of carbon dioxide for methane in gas hydrate upon injection of liquid carbon dioxide into a porous medium initially saturated with methane and its hydrate. Self-similar solutions of the axisymmetric problems that describe the distribution of the main parameters of the bed are constructed. It is shown that there are solutions, according to which the process can occur both with and without boiling of carbon dioxide. Diagrams of the existence of each type of solution are constructed.

The interaction of the cooling systems of permeable materials with a high-temperature gas flow is considered. The effect of the porosity and thermal properties of some metals on heat transfer is investigated.яIt is found that increasing the thermal conductivity of the material leads to a decrease in the temperature of the heat-shielding coating and increasing the porosity to a more uniform distribution of the coolant applied on the surface and to a decrease in the heat loads on the structure to be protected.

This research is aimed at studying the two-phase flow pattern of a top heat mode closed loop oscillating heat pipe with check valves. The working fluids used are ethanol and R141b and R11 coolants with a filling ratio of 50% of the total volume. It is found that the maximum heat flux occurs for the R11 coolant used as the working fluid in the case with the inner diameter of 1.8 mm, inclination angle of -90 ͦ, evaporator temperature of 125gr, and evaporator length of 50 mm. The internal flow patterns are found to be slug flow/disperse bubble flow/annular flow, slug flow/disperse bubble flow/churn flow, slug flow/bubble flow/annular flow, slug flow/disperse bubble flow, bubble flow/annular flow, and slug flow/annular flow.

A method and an experimental setup are developed for determining the intensity of evaporation from the free surface of water. During the measurement, the ambient air velocity and the water temperature can be varied. The mass and temperature of water, as well as the temperature, pressure, and humidity of the ambient air are measured as functions of time. The evaporation rates are calculated from the measured and recorded data in the cases of natural and forced convection.

The torsional and longitudinal flexural vibrations of orthotropic corrugated shells are investigated. Relations, including the equation of motion in forces and moments and the Hooke's law relations are obtained using the Kirchhoff-Love hypotheses. The influence of geometric parameters of the shell (amplitude and length of the corrugation) on the natural frequencies and natural vibrations modes are studied for fixed-end shells.It is found that during torsional vibrations, increasing the amplitude of the corrugation and increasing the number of corrugations leads to a decrease in the resonant frequencies. In the case of torsional and longitudinal flexural vibrations, the influence of the corrugation amplitude on the natural vibration modes is investigated.

The previously proposed method of one-dimensional deformation of soil is used to solve the problems of joint seismic vibrations of an underground pipeline and elastic soil under nonideal contact under the assumption that there is slip on the contact surface and that resulting shear stresses on it are proportional either to the relative displacement of soil particles and pipeline or to the relative speed of motion movement. The dependence of the maximum stress in the pipeline on the coefficients under boundary conditions is investigated. For supersonic flow around the pipe, resonance is observed with decreasing shear stress on the contact surface.

The Ramberg-Osgood stress-strain relation is used to perform a theoretical springback analysis in the problem of bending of a narrow rectangular strip made of a strain-hardening material. The maximum strip thickness is 5 mm, and its length is significantly greater than the thickness. Based on the elasticity and plasticity deformation theory and also on the Tresca and von Mises yield criteria, an expression for the springback ratio is derived. The springback ratio depends on the ratio of the yield stress to Young's modulus, Poisson's ratio, strain hardening coefficient, and sheet thickness.

The boundary-value problem of the elasticity theory for a cylinder with cylindrical cavities forming a hexagonal structure is under consideration. The solution is constructed in the form of a superposition of accurate basic equations of the Lame equations for a cylinder in the coordinate systems associated to the centers of the body surfaces. The boundary conditions of the problem are satisfied exactly with the help of the generalized Fourier method. The problem is reduced to an infinite system of linear algebraic equations with a Fredholm operator in the space l₂. The resolving system is solved numerically by the reduction method. The numerical analysis of stresses in the regions of their greatest concentration is carried out.