Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2026 number 3

Various failure modes of the electrodes and insulators of pulsed X-ray tubes with explosive electron emission operating in a single-pulse flash mode are investigated. The operating parameters are as follows: capacitor bank discharge energy into the tube 30-50 J, pulse duration 40-100 ns, and electron energy incident on the anode 200-300 keV. The following experimentally observed damage types are identified: sublimation, spallation, surface melting, formation of Taylor cones drawn from the surface, droplet ejection, surface etching in the form of deep longitudinal grooves, periodic chevron-like surface patterns, deep surface cracks, micrometer-scale droplets atop Taylor cones that have traveled from the cathode to the anode, cathode bombardment by material ejected from the anode, dust-like deposition in the form of island films on the cathode and insulator, and surface flashover along the insulator accompanied by film evaporation. The mechanisms underlying the effects of high-current pulsed electron beams on the components and the influence of these damage types on the service life of the tubes are discussed.

A comprehensive experimental study aimed at generating a training dataset for the development of a neural network model to optimize the control of environmental and energy performance parameters of hydrocarbon fuel flame combustion is presented. Flame characteristics are investigated for liquid fuel combustion using a flare burner with a thermal capacity of 300-1500 kW and mechanical atomization. The experiments examine operating modes at various power levels (400, 700, and 1000 kW) and equivalence ratios (1.06, 1.17, 1.28, and 1.40). Simultaneous measurements of flame temperature, combustion product gas composition analysis, and visual flame monitoring are performed. The dependence of combustion parameters on operating conditions is established: an increase in power and a decrease in the equivalence ratio elevate the flame temperature. Alternatively, dropping airflow reduces CO concentration to <10 mg/m³ but increases NO_x emissions to >125 mg/m³. Correlations between the visual flame characteristics (size and luminous intensity) and the equipment operating parameters are identified, which opens prospects for the development of automated machine-vision-based control systems.

An asymptotic model of large-amplitude stationary inertial waves in an axisymmetric swirling flow of an ideal fluid in a circular pipe of varying diameter is developed. Calculations are performed for a flow with solid-body rotation far upstream; in this case, vortex breakdown is caused by the pipe geometry and the emergence of a separation zone. The separation zone is shown to be axially asymmetric. For a separation region to form at a fixed position relative to the onset of pipe expansion, the flow swirl should be stronger for larger pipe expansion angles.

Results of an experimental study on the effectiveness of controlling incompressible turbulent flow over an asymmetric Clark Z airfoil using a perforated surface are presented. The perforated surface consists of an array of cylindrical cavities or through-holes with variable geometric parameters. The cavities are located on the lower surface of the wing, most of which is exposed to zero-pressure-gradient flow. The study is conducted over a chord Reynolds number range of Re_c = (0.601-1.324) × 10⁶ at an angle of attack of 3.6°, corresponding to a momentum thickness Reynolds number range at the perforated surface inlet Re_θ = 527-992. Particular attention is given to a previously unexplored analysis of the potential for reducing the aerodynamic drag of the airfoil under these conditions. It is shown that none of the perforated surface configurations under study provides a drag reduction within the experimental uncertainty.

The development of a single thermal disturbance in a laminar boundary layer at a Mach number M = 1.43 in the presence of a pressure gradient induced by a shock wave emanating from a wedge with an angle of 2° is investigated using direct numerical simulation. Calculations are performed using the HyCFS-R code developed at the ITAM SB RAS. The evolution of the disturbance is examined in a zero-pressure-gradient boundary layer, during passage through the interaction region, and in the wake. A single thermal disturbance is shown to generate a localized wave packet. Spectral analysis is used to determine the packet composition and its evolution through the interaction zone. The influence of the pressure gradient on disturbance amplification is assessed, and the disturbance development in the boundary-layer-shock-wave interaction region up to the onset of laminar-turbulent transition is analyzed. A comparative analysis is performed for two types of boundary conditions applied at the lateral boundaries of the computational domain. The results show that the combined effect of the thermal disturbance and the shock wave plays a dominant role in boundary-layer destabilization, which should be taken into account in transition control strategies for supersonic flows.

The flow structure and pressure fluctuation characteristics generated when a supersonic underexpanded jet impinges on a flat semi-infinite obstacle with a coaxial hole are investigated. Different interaction regimes are found to arise depending on the hole diameter and the distance from the nozzle exit to the obstacle. The presence of a hole in the obstacle is found to significantly intensify wall pressure fluctuations for nozzle-to-obstacle distances in the following range: h/D_a = 1-4. In the case where h/D_a = 4-15, the interaction regimes are similar to those observed for a jet impinging on a solid (impermeable) obstacle.

This paper presents the results of a study of the parachute -type fragmentation process. This process serves as a source of the dispersed phase in various natural and industrial multiphase flows in which a planar liquid surface is exposed to a gas stream. Experiments are performed using shadowgraph visualization and high-speed imaging, with artificial initiation of the process under controlled conditions. Computer-based image processing is used to determine the dome dimensions and film thickness, as well as to detect the resulting droplets and quantify their number. Based on the analysis of the results, it is concluded that rupture of the dome film occurs due to Rayleigh-Taylor instability. The dependence of the average number of droplets produced by rupture of the parachute dome film on the governing parameter-the Weber number-is obtained.

The effect of free rotation of the cylindrical housing of a centrifugal reactor on the structure of vortex fluid flow is investigated experimentally. The working fluid is driven by rotation of the upper disk, while the reactor housing is free to rotate about its axis under the action of viscous friction from the fluid. The flow energy expended in overcoming friction in the stationary housing is converted into kinetic energy of rotation of the reactor housing. Even slight free rotation of the reactor housing is found to lead to a significant intensification of the vortex motion. The proposed reactor design enables efficient control of vortex flows without the additional energy expenditure required for forced rotation of the sidewalls at a fixed speed. The results obtained can be used in the development of compact centrifugal reactors for biological, chemical, and energy technologies.

Forced nonlinear oscillations of a gas bubble in a viscoelastic fluid are considered for the case where the oscillation frequency of the external fluid pressure coincides with the undamped linear resonant frequency of the bubble. The averaging method is applied to derive a formula for the dependence of the bubble oscillation amplitude on the external pressure amplitude, the adiabatic exponent, and the viscoelastic properties of the fluid. Computational results obtained using this formula are shown to be in good agreement with numerical simulation results.

The variable N-factor method, which is one of the most effective modern approaches for predicting the laminar-turbulent transition location in boundary layers, is improved. The determination of the threshold N-factor for swept wings is refined by taking into account the range of transverse roughness scales on the wing leading edge that are dangerous from the standpoint of cross-flow instability and boundary-layer receptivity. The proposed modification does not require additional numerical analysis, as it is based on standard linear stability theory calculations and empirical data on the efficiency of boundary-layer receptivity to roughness in the generation of cross-flow instability vortices. The resulting dependences of the critical N-factor on the dimensionless leading-edge roughness are presented and calibrated against our own experimental data.

The interaction of a plane oblique shock wave with a vortex system arising from flow separation at the edge of a dihedral model with an opening angle of 270° is examined. The shock generator, which is a thin plate, and the model are positioned at the same angle of attack of 16°. A downstream-expanding separation vortex is generated by the pressure difference between the upper and side faces of the model, while the shock wave incident from the generator causes extensive boundary-layer separation on the surface of the side face. The complex interaction between the shock-induced separated flow and the stalled flow leads to the formation of a cylindrical vortex detached from the surface.

The effect of preloading on the porosity change of water-saturated clay soils is investigated. A numerical model of one-dimensional filtration in a porous medium with variable permeability dependent on the applied load is employed for the analysis. The boundary conditions are specified in terms of filtration velocities, and the load effect is modeled through changes in the permeability coefficient. The results obtained are shown to be in good agreement with experimental data. The proposed description of porosity evolution enables more accurate prediction of soil behavior during fluid filtration.

A numerical study of the problem of symmetric capillary filling with a viscous incompressible fluid in the nonisothermal case is performed. The flow is described using the Pavlovskii model. In this problem, the dynamic contact angle issue arises when the impingement angle differs from 0 or π. This issue originates from the incompatibility between the free-surface boundary conditions and the no-slip condition on the solid wall in the vicinity of the moving three-phase contact line. To close the formulation, the no-slip condition is replaced by a generalized Navier slip condition. The influence of the dynamic contact angle on the temperature near the three-phase contact line is investigated for flows with low capillary numbers.

A method for controlling the heat flux density during boiling of water in the context of modeling a two-phase cooling system for power electronics is examined. The challenge of increasing thermal loads and amplifying power devices lies in the inability to remove such high heat fluxes from the power module. The most efficient heat removal mechanism, boiling, is limited by the onset of a boiling crisis. A simplified method for enhancing vapor removal from the heat transfer surface using adiabatic inserts is proposed. The inserts break up vapor bubbles into smaller ones, reducing the likelihood of vapor film formation on the surface. Additionally, they promote liquid sliding along the unheated isothermal insert wall, unimpeded by vapor bubbles. The primary experimental technique is gradient heatmetry. The dependence of the local heat flux density on the simulated power module temperature is obtained for various fin pitches with adiabatic inserts. The effectiveness of the proposed heat flux density control method is demonstrated.

Results of a numerical analysis of the transition from steady to oscillatory laminar flow in gravitational convection of an incompressible fluid in a closed cavity heated from the side are presented for various Grashof and Prandtl numbers. The influence of the nonlinear dependence of convective flow on the Prandtl number on the flow structure and its temperature and concentration stratification is demonstrated.

The influence of tube walls on laser-induced subcooled boiling at the end of a thin laser fiber placed in a tube is investigated numerically. It is shown that, in the case of tubes with a radius fourfold greater than the bubble radius at maximum expansion, the velocity of the cumulative jet formed upon collapse of the vapor bubble is equal to that in an unbounded space. As the tube radius decreases, the jet velocity decreases due to rebound , which is bubble re-expansion that prevents jet formation. A further reduction in radius leads to a predominance of axial fluid flow within the tube and subsequent jet destruction. The influence of tube radius and length, as well as fiber length, on the bubble shape and volumetric flow rates through the tube end sections is demonstrated. Dimensionless parameters at which the volumetric flow rate through these sections reaches its maximum are identified, which is particularly important for medical applications.

Heterogeneous boron carbide-based ceramics with vanadium diboride additions, produced by uniaxial hot pressing, are investigated. During sintering, vanadium diboride was synthesized by carboborothermic reduction from vanadium oxide, as confirmed by X-ray diffraction analysis. The microstructure of the B₄C-VB₂ heterogeneous ceramics consists of uniformly distributed vanadium diboride grains in a boron carbide matrix. Increasing the vanadium diboride molar fraction from 0 to 5% is found to increase the fracture toughness of the ceramics from 2.0 to 5.5 MPa·m^1/2.

This paper describes the Love wave propagation in a layer overlying a half-space consisting of relatively thin layers, with slip at the contact boundaries. The slip contact conditions in the finely layered medium are specified by a linear Winkler-type condition for shear stresses. This medium is described by an asymptotically exact homogenized model that includes second-order terms in a small parameter-the layer thickness. Dispersion relations for Love waves are derived. Typical dispersion curves and through-thickness wave profiles are constructed. A parametric analysis is performed, revealing differences from the case of a homogeneous half-space.

The characteristics of the elastoplastic transition and subsequent hardening in the strain curve segment up to 4% deformation are investigated in homogeneous AMg5 alloy specimens and in specimens containing a friction stir weld. Depending on the strain rate, the elastoplastic transition is found to occur through the formation and propagation of localized plasticity autowaves of switching or excitation types. These autowaves form at stress concentrators, such as weld seam boundaries.

A specialized experimental facility developed by the authors is described. The facility enables in vitro blood flow studies in vascular sections of various configurations while maintaining similarity to real hemodynamic conditions. Results of its performance evaluation are presented. The facility is shown to have several advantages over existing analogs. It enables flow visualization and measurements of flow parameters under both steady and pulsating conditions. The facility produces a waveform that matches the actual blood flow variation over a cardiac cycle, including a high-amplitude antegrade flow peak and a retrograde flow (flow rate reversal) segment. It also demonstrates stability and high reproducibility of the specified operating conditions. Experimental results obtained with this facility can be used to validate existing and future numerical models of vascular hemodynamics.

The process of blood pumping through an artificial vessel using a vibro-volumetric perfusion pump is investigated. The device is essentially an expanding channel with vibrating walls, approximating a diffuser in its simplest form. The relationship between the vibration parameters and the geometric characteristics of the device and the flow rate of transported blood is examined. A mathematical perfusion model is presented. This model incorporates a three-component rheological model of blood and a two-mass model of the oscillatory system of the device. The interaction between the vibrating walls, the deformable vessel, and the blood are also accounted for in the model presented.