Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2024 number 1

The characteristics of the combustion process of liquid (diesel) fuel in a high-speed jet of superheated water vapor in the combustion chamber of a hot water boiler are studied at a thermal power of the burner device approximately equal to 40 kW. It is shown that the burner device, created on the basis of the technology of fuel atomization with a steam jet, meets modern technical and environmental standards and has a number of advantages over analogues. It has been established that the addition of steam makes it possible to reduce the concentration of CO and NO_x in combustion products several times. At the same time, the volume of emissions of carbon monoxide and nitrogen oxides when using the burner design under study is significantly (2.5 and 1.4 times, respectively) less than when using a serial analogue of the Weishaupt burner device. Recommendations for optimizing the operation of such devices are presented.

This paper presents the results of an experimental study of the breakup of a jet consisting of two coaxial jets of immiscible liquids with varying phase flow rates. Distilled water and a mixture of polymethylsiloxanes were used as working liquids. The regimes of jet breakup, the types of capsules formed, and the sizes of single-chamber capsules formed under the influence of capillary instability were determined. The natural frequencies of surface instability were measured.

Results of tensile and low-cycle fatigue testing of samples made of an aluminum-lithium alloy of the Al-Mg-Li system obtained by plasma-assisted laser cutting performed by a pulsed CO₂ laser in an argon jet with the laser beam and optical discharge plasma simultaneously affecting the material are reported. Low-cycle fatigue tests show that the number of loading cycles survived by the sample obtained by plasma-assisted laser cutting is more than twice greater than the number of cycles survived by the samples obtained by conventional laser cutting with continuous radiation.

This paper presents a solution of the two-dimensional non-stationary problem of the development of wave motion in a two-layer liquid of finite depth under ice cover modeled by a thin elastic plate taking into account longitudinal compression forces. The cases are considered where, in the unperturbed state, one of the layers is at rest and in the other (top or bottom) layer, the horizontal flow velocity varies linearly in thickness. Dispersion dependences were determined for three wave modes arising in the presence of shear flow. The vertical deflections of the ice cover due to a pulsating source of disturbances located in an initially motionless layer of liquid were calculated. A special case is also considered where the liquid is bounded at the top by a solid lid. The problem is considered in a linear formulation, and the liquid is assumed to be ideal and incompressible.

The influence of the jet pressure ratio ( n =1.18÷3.35) in a nonisobaric supersonic jet of a vibrationally excited gas SF6 exhausting from a convergent axisymmetric nozzle 0.25 mm in diameter is studied numerically and experimentally. The experiments aimed at studying the gas-dynamic structure of the jets are performed in a specially designed jet setup of the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences. The numerical simulations are performed by solving two-dimensional Navier-Stokes equations within the framework of the ANSYS Fluent software and the thermally perfect gas model. The influence of excitation of vibrational degrees of freedom of the SF6 gas is studied in both an equilibrium gas and vibrationally nonequilibrium gas. The nonequilibrium state of vibrational degrees of freedom is simulated with the use of a two-temperature model of relaxation flows. It is shown that the jet pressure ratio of the SF6 gas affects the length of the wave structure cells, which is responsible for the change in the vibrational relaxation rate. The coefficient of density amplitude reduction in gas-dynamic cells is derived as a function of the jet pressure ratio.

The movement of dissolved salt in melting snow is considered based on the equations of non-isothermal two-phase filtration. The thermal conductivity of snow and dependence of the water freezing temperature on salinity were verified against available experimental data. The influence of the presence of dissolved salt on the phase transition was evaluated by numerical experiments.

The influence of the amplitude of deflectors introduced into a laminar jet flow on the coefficient of linear change in the radial component of a stationary disturbance is investigated. The method for introducing disturbances and the method for measuring them are described. It is shown that a decrease in the amplitude of the deflectors does not lead to a change in the flow pattern, does not prevent the occurrence of an algebraic growth mechanism, and causes a proportional decrease in the radial component of the stationary velocity disturbance. The transition to the turbulent regime occurs after reaching a certain value of the radial expansion, which does not depend on the initial amplitude of the introduced disturbance.

The paper presents the results of an experimental study of the influence of distributed engines mounted downstream of the trailing edge on the structure of a separated flow around a trapezoidal model of a flying wing in a subsonic wind tunnel. Visualization patterns of the near-wall flow on the leeward side of the model are obtained in the modes of blocked engines and for the rotational speed of the impeller of 32800 rpm in the range of angles of attack of the wing α = 5÷20°. The studies also take into account the location of distributed propulsion relative to the level of the trailing edge, where the axis of rotation of the engine impeller coincided with the continuation of the wing chord line or is higher than that. The possibility of controlling a separated flow by using sources of stationary disturbances in the form of cones and ribs locally mounted at singular points on the wing surface is studied.

The efficiency of fluid atomization by an atomizer is studied as a function of the spray energy. The dependence of the maximum values of energy on the fluid flow rate is analyzed. A linear dependence is obtained for flow rates smaller than 80 g/s, which testifies to a high efficiency of fluid atomization. For flow rates greater than 80 g/s, the droplet energy is seen to decrease drastically, leading to an increase in the spray droplet size, which testified that the atomization quality is deteriorated. This behavior is observed in all regimes considered in the study.

The local flow structure in a turbulent gas-droplet flow behind a single obstacle has been studied numerically for different initial mass concentrations and diameters of dispersed particles. The effect of evaporating droplets flowing around a single square obstacle on the local averaged and pulsating flow structure and the dispersed phase propagation process has been analyzed. The profiles of averaged longitudinal velocity components of the gas and dispersed phases are similar to those for the single-phase flow regime. The gas velocity in the gas-droplet flow is insignificantly (less than 3%) higher than the corresponding value in the single-phase flow. The turbulence kinetic energy increases in approaching the obstacle. Maximum gas-phase turbulence was obtained on an obstacle of height h at x / h = -1÷0, and it is more than 50% higher than the turbulence kinetic energy before and after the obstacle.

An approach is proposed to model hemodynamics in an arteriovenous malformation and its vascular environment during neurosurgical embolization. This approach is based on a combination of the filtration model of blood flow and the embolic agent in the malformation with a hydraulic approach for the vessels surrounding the malformation. The model is described mathematically by a system of integrodifferential hyperbolic equations. The parameters and functions included in the model are determined using real clinical data from patients. Based on the model, the problem of optimal control of multistage embolization was formulated and studied numerically. Optimal embolization regimens were found for which there is good agreement between the calculated and clinical data. The proposed approach can be used to develop preoperative recommendations about the optimal tactics of surgical intervention.

The sizes and rise velocity of bubbles in a stationary liquid in an inclined channel with a circular cross-section at various gas flow rates through a capillary were determined (3.0÷5. ml/min). The sizes and velocity of gas bubbles was studied by shadow photography. It is shown that in the range of channel inclination angles 40÷60°, the formation of stable bubble structures-clusters consisting of bubbles of the same size (1.5÷1.8 mm) - can be formed. In modes without the formation of chain clusters, the average diameter of gas bubbles increased (2.0÷2.2 mm) due to their coalescence.

Direct numerical modeling is used to study the effect of wall heating on the characteristics of reverse wall flow that occurs during turbulent flow of various coolants in a channel with a square cross-section. The temperature field is considered both in the passive impurity approximation and in the low Mach number approximation. Qualitative and quantitative results were obtained characterizing the probability of the occurrence of reverse wall flows in all considered cases at the Reynolds number Re = 3150, calculated from the average flow velocity and half-height of the channel. It has been established that in the considered cases, heating of the walls leads to an increase in the probability of the formation of reverse wall flows by an average of 2-3 times.

Using previously obtained analytical formulas for the natural frequencies and vibration modes of inhomogeneous rods with a variable cross-section (corset shape), the geometric and elastic characteristics of the samples were determined, and the amplitudes of axial stresses obtained during experimental studies of the fatigue strength of metal alloys under high-frequency cyclic loading were assessed. Based on a three-mode model of fatigue failure, a numerical method is proposed for calculating the kinetics of damage under high-frequency cyclic tensile-compression loading of corset-shaped specimens at different values of the cycle asymmetry coefficient. The results of calculations using the proposed model are compared with the results of experiments on corset-shaped samples made of titanium alloy. The proposed model and calculation method make it possible to construct fatigue curves with sufficient accuracy for various cyclic loading modes and cycle asymmetry coefficients. To do this, it is enough to know the base points of the bimodal fatigue curve for the reverse cycle.

Nonlinear vibrations, buckling, and aeroelasticity of a thin nonlinear orthotropic composite plate have been analyzed. The types of symmetric and antisymmetric sheet layering, the number of layers, the fiber angle ranging from 0 to 90°, the effect of constant and variable thermal loads, the temperature dependence of the specific heat coefficient and the elastic modulus of the material, along with the local geometrical defects have been investigated. Using Galerkin's weighted residual theory, partial differential equations have been transformed into nonlinear ordinary differential equations, which are solved by the Runge-Kutta method.

The heat conduction equation of the coupled dynamic theory of thermoelasticity is considered. An assessment is made of the connectivity in the heat conduction equation for a space with a constant initial temperature, containing a flat semi-infinite crack moving at a constant speed, on the sides of which a constant temperature is instantly established, less than the initial one (thermal shock). The movement of a crack and thermal shock on its shores determine dynamic effects that must be taken into account to assess connectivity in the thermal conductivity equation. It is shown that, under real conditions of thermal impact on massive bodies with cracks, dynamic effects and cohesion for materials that satisfy certain conditions imposed on their thermomechanical constants can be neglected, which makes it possible to significantly simplify the solution of problems of thermoelasticity for such bodies.

The problem of forced bending vibrations of a rod-strip with two consoles and a fixed section of finite length on one of the front surfaces is solved. To describe the processes of deformation of consoles, the Timoshenko model is used without taking into account transverse compression and a fixed section - the same deformation model taking into account transverse compression, modified by taking into account the presence of a fixed fixed section. The conditions for the kinematic coupling of the consoles and the fixed section are formulated. Based on the Hamilton-Ostrogradsky variational principle, the equations of motion and boundary conditions, as well as the force conditions for the coupling of sections of the rod, are formulated. Exact analytical solutions of the equations of motion under the influence of a harmonic transverse force at the end of one of the rod consoles are obtained. Numerical experiments were carried out in which the passage of resonant vibrations through a fixed section of finite length in rods made of duralumin and fiber composite was studied, with and without taking into account the transverse compression of the fixed section. A significant increase in the vibration amplitude of the end of the unloaded cantilever of a duralumin rod was discovered due to transverse compression of the fixed section. For a composite rod, the vibration amplitude increased slightly.

The results of experimental measurements of the flame temperature in the presence of an impact surface and a liquid phase added to the flow are presented. Methods based on laser-induced fluorescence were used to measure temperature. For a flame of a pre-mixed methane-air mixture with values of the stoichiometric coefficient Φ = 0.92 and Reynolds number Re = 1000, a reverse flow zone was detected near the impact surface in the case when this surface is located at a distance from the nozzle exit equal to three calibers. The temperature field of a gas-droplet flame was measured using the laser-induced fluorescence method