Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2024 number 4

The processes of spraying, spatial propagation, and deposition of aerosol particles generated impulsively using the energy of energetic materials. Such aerosols are produced for the purpose of decontaminating harmful gases or aerosol formations. A mathematical description of the evolution of the decontaminating aerosol cloud is proposed, and the results of experiments on spraying an aerosol of titanium oxide particles are presented.

New modifications of helical generators with meander shaped striplines have been proposed, which allow the inductive and capacitive parts of the generator to be separated in space. The proposed change allows separate regulation of the characteristic impedance of a double-bus helical line and the generator inductance and winding capacity. The characteristics of the generators have been studied experimental, and theoretical models adequately describing the operation of these devices have been proposed. The developed generators can be used to produce pulsed X-ray devices with explosive electron emission.

This paper presents the results of calculations of liner implosion without the formation of shock waves under the influence of a current up to 70 MA and a magnetic field induction up to 20 MGs (magnetic pressure up to 16 Mbar) in devices with a disk explosive magnetic generator. It is shown that during deep implosion of two-layer (Cu-W) and (Cu-Ta) liners, the shockless pressure in tungsten and tantalum can reach 40 Mbar (hydrodynamic cumulation). The inner part of the liner, whose mass is more than 32% of its total mass, may remain in a solid-state dynamically strengthened state at a temperature of its copper skin layer up to 38 eV.

The impact interaction of composite projectiles with thin metal plates is studied, and a method for evaluating the ballistic limit and residual velocity of the projectile is proposed. The composite cylindrical projectile consists of a deformable highly porous nose part and a hard non-deformable tail. The velocity of the projectile is considered in the range 200-850 m/s. The problem is solved numerically in a two-dimensional axisymmetric formulation. The motion of the medium is described using the Lagrange method. The calculation results are compared with experimental data. It is shown that the results obtained are in good agreement with the results of calculations using available analytical models and experimental data.

An analytical (exact) solution of equations of a two-dimensional boundary layer of a non-Newtonian viscous fluid in the case with mass transfer is obtained with the use of the Ostwald-Reiner power-law model in a particular case with n = 2 (dilatant fluid). It is noted that the apparent viscosity in this case is described by an expression that coincides with the equation for turbulent viscosity of a Newtonian fluid derived by the Prandtl mixing length model. For the particular case under consideration, it is found that there is an analogy between the flows of a non-Newtonian fluid and a Newtonian fluid with turbulent viscosity.

The laminar--turbulent transition in transonic flows is studied with the use of thin-film surface hot-wire probes. For determining oscillations recorded by the thin-film probe in the boundary layer, coherence spectra are constructed between the data obtained by the thin-film probe and by the hot-wire probe, which was used to perform measurements across the entire boundary layer. Based on the analysis of these spectra, it is demonstrated that the most accurate and complete data are obtained by the thin-film probe in the intermittency region.

The dynamics of an acoustic signal passing through a bubble curtain has been studied by mathematical modeling. The case is considered where the gas (methane) inside the bubbles is under hydrate formation conditions. The effects of the hydrate formation process, the initial radius of bubbles, and the volume gas fraction on the attenuation coefficient and phase velocity of the wave propagating in a deep-water sea (located at a large depth) bubble curtain are investigated. The reflection and transmission coefficients of acoustic waves at the boundaries separating single- and two-phase regions are obtained. It is found that the hydrate formation process increases the wave attenuation coefficient by more than two orders of magnitude at low frequencies (below 1 kHz).

Distributions of the amplitude of controlled disturbances in space and time and their frequency-wave characteristics are obtained from experimental results on weakly nonlinear development of the wave train in the region of a stationary wake inside the boundary layer on a flat plate at the Mach number M = 2. A stationary streamwise disturbance is generated by a pair of weak oblique shock waves. Controlled disturbances are inserted into the flow by a local high-frequency glow discharge located inside the model. The development of controlled disturbances is analyzed on the basis of the linear theory of hydrodynamic stability. Typical resonant wave triplets are identified. It is found that flow inhomogeneity suppresses the mechanisms of interaction of controlled disturbances.

The results of a numerical study of heat transfer in a gas-droplet turbulent flow behind a single square barrier with variations in the initial mass concentration and diameter of dispersed phase particles are presented. When flowing around a barrier, adding droplets to the flow leads to a significant intensification of heat transfer (almost twice) compared to a single-phase air flow. It is shown that when a two-phase flow flows around a transverse barrier, the coordinates of the maximum heat transfer intensity and the flow reattachment point differ by approximately 12%. An increase in the barrier height leads to a decrease in heat transfer intensity.

For a nonlinear parabolic reaction - diffusion system, solutions are constructed and investigated that have the form of a diffusion wave propagating in a medium at rest with a finite velocity. For the first time, for cases of spherical and cylindrical symmetry, the problem of initiating a diffusion wave by boundary conditions specified on a sphere (circular cylindrical surface) is considered. A theorem of existence and uniqueness of a solution in the class of analytic functions is proved. An exact solution is constructed, which is presented in the form of explicit formulas. A step-by-step iterative algorithm is proposed, based on the collocation method and expansion in radial basis functions. Numerical calculations are performed, for the verification of the results of which the exact solution is used.

The influence of spanwise-uniform roughness elements (streaks) on the transition to turbulence in the boundary layer on a swept wing with domination of crossflow instability in the presence of unsteady and steady free-stream vortices is studied. The measurements are performed for rectangular (in the plane parallel to the flow and normal to the wall) roughness elements shaped as streaks of different heights, which have two different widths in the chord direction. The experiments are performed in a low-turbulence wind tunnel at low subsonic velocities of the incident flow with the use of hot-wire anemometry. The studies are conducted in the range of unit Reynolds numbers (based on the streamwise component of velocity at the boundary layer edge at the beginning of the rough surface region) 0.687 ·10⁶ - 1.568 · 10⁶ 1/m. The results are obtained in 76 regimes of measurements for two types of free-stream vortex disturbances generated by two turbulizing grids: with domination of unsteady disturbances and combination of steady and unsteady disturbances.

Modern approaches to visualization and automatic identification of regions are discussed separation of three-dimensional boundary layers. The corresponding algorithms are implemented within the framework of the original LOTRAN software package, designed to calculate the position of the laminar-turbulent transition in boundary layers over surfaces of small curvature. Their work is demonstrated using two configurations: a swept wing and a prolate spheroid.

In this study, the thermal and fluid flow characteristics of a piezoelectric fan are experimentally evaluated by altering its height and distance from single-fin and plate-fin heat sinks. Based on the thermal resistance of heat sinks, the piezoelectric fan performance is assessed. Particle image velocimetry is used to study the flow velocity field generated by the piezoelectric fan.

This study is aimed at optimizing the design parameters (winding angle, fiber volume fraction, elasticity modulus of fibers, and radius-thickness ratio) of the fiber-wound pressure vessel for achieving a stable strength ratio based on a hybrid method of Particle Swarm Optimization and Grey Wolf Optimization (HPSOGWO). A three-dimensional linear elasticity theory is used to solve the problem numerically.

It is proposed to use a curvilinear triangular finite element with a small number of degrees of freedom to reduce the amount of calculations in solving problems of the numerical nonlinear dynamics of shells using step-by-step integration over time. The compactness of the finite-element formulation is achieved by applying strain-tensor invariants. This is done using natural deformation components which are determined in the directions of three coordinate lines parallel to the sides of the element. Solutions describing large displacements, rotation angles, and buckling dynamics are given to analyze the capabilities of the proposed finite-element model.

The influence of the main parameters of the nonlocal continuum model on the stress concentration was studied when solving the problem of stretching a plate with an elliptical cutout in its center, also called the Kirsch problem. The influence of thermal expansion of the medium on the stress-strain state of the plate was studied. The obtained results were compared with the classical ones. It was shown that the maximum stress and heat flux density decrease, and the deformation in the stress concentration zones increases.

The paper describes a methodology for the experimental study of a powerful heat release in a microsized probe immersed in a two-component solution with a lower critical solution temperature. Experimental data on overheating relative to the liquid - liquid spinodal and thermal impact on the stability of the system for a water - PPG-425 solution are presented. The following conclusion is made for a solution whose near-critical mass fraction of PPG-425 is 30%: despite the high density of the heat flux through the heater surface (9.2-13.7 W/m²), its temperature stabilizes at a value exceeding the equilibrium temperature of the liquid - liquid system by approximately 150 K. It is shown that the heat exchange process is stable against changes in the heating parameters: the nature of heat transfer by the solution remains the same. It is revealed that the heat transfer coefficient is several times greater than the corresponding value obtained for water.

For the spray of a single-component fluid (water) from a simplex atomizer, dependences of the mean size, mean velocity, and frequency of droplet registration on the pressure and method supplying the power fluid into the simplex channels were obtained by the local time-shift method using a SpraySpy device. Visual analysis of the effect of adding a fluid (kerosene) immiscible at the molecular level with water on the structure and decay of the spray cone was carried out by shadow photography. It was found that the two-component emulsion disintegrates in the close proximity of the atomizer outlet orifice almost at once, resulting in significant deformation of the spray cone.