Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2026 number 4

A method is proposed for estimating the energy expenditure associated with air injection through a cylindrical section of a finely perforated surface on a high-aspect-ratio body of revolution at zero angle of attack in an incompressible flow. The method is based on the premise that the power required for injection is independent of both the power of the propulsion engine and the motion regime of the body. For a Reynolds number Re₁ = 1.666 × 10⁶ m^-1, numerical simulations demonstrate that distributed air injection into the turbulent boundary layer of the body of revolution can yield power savings of 11 to 19 %, depending on the size of the computational domain.

Results of an experimental investigation of coherent structures in a shear layer, obtained using different approaches, are presented. Characteristic length scales are determined via combined processing of data from single-wire and surface hot-film anemometers and PIV measurements. The combined PIV and surface anemometry approach allows one to identify regions where the flow parameters correlate with the readings of the surface sensors. The joint analysis of data from the surface sensors and PIV enabled determination of the optimal location of the surface sensors relative to the separation region for the development of active closed-loop flow control techniques.

We investigate the superposition of two unsteady one-dimensional shear flows of a homogeneous Newtonian viscous fluid in a half-space with a boundary that translationally moves parallel to itself. Exact solutions are expressed in terms of Stieltjes integrals in a quasi-self-similar form characteristic of diffusion-vortex processes. A linearized perturbation problem is formulated in terms of velocity and pressure variations, assuming the motion of the boundary plane remains unperturbed. This problem is analyzed using the method of integral relations. The method employs quadratic functionals and yields integral estimates sufficient to ensure that perturbations do not grow over an infinite time interval. The case in which both boundary velocity components are monotonically nondecreasing functions of time is examined analytically.

A numerical study of the effect of mixer configuration on the flow structure and mixing quality of a rheologically complex fluid in a mixing apparatus is performed in a two-dimensional formulation. Three mixer configurations are considered: paddle, anchor, and anchor with rotation. The non-Newtonian behavior of the fluid is described using the power-law model. The solution is obtained using the finite-volume method with the SIMPLE pressure-correction procedure, implemented on an unstructured triangular mesh. The flow structure is characterized by the formation of circulation zones near the blades and a shear-flow region along the solid wall of the apparatus. The redistribution of an ensemble of marker particles over time is also simulated to enable a qualitative assessment of the mixing process. A quantitative assessment is performed using a measure of marker distribution inhomogeneity.

The problem of surface wave propagation in the presence of a thick rectangular block floating above an infinite step is studied within the framework of linear theory. The block is located entirely in the region of finite depth. An eigenfunction expansion method is used to construct the velocity potential describing the fluid motion in the finite- and infinite-depth regions. From the pressure continuity conditions in the gaps above the step corner and below the two corners of the block, three integral equations of the first kind are derived for the horizontal velocity components in these gaps. The integral equations are solved using the Galerkin method, the basis functions are chosen as simple polynomials multiplied by exponentially decaying functions, and the weight functions are determined taking into account the edge conditions. We perform the numerical calculations of the hydrodynamic characteristics-the reflection and transmission coefficients and the components of the wave force acting on the block. The dependences on the wave number are obtained and analyzed.

A new microcapsule design for targeted drug delivery is proposed and investigated. The design consists of a spherical liquid cell (drug solution) containing a nanobubble, encapsulated in a polymer shell. The effect of low- and high-frequency ultrasound on the cavitation bubble dynamics in a confined liquid volume and the resulting elastic tangential (circumferential) stresses in the polymer shell is analyzed. It is found that a relatively weak external ultrasound stimulus can be significantly amplified inside the microcapsule due to explosive cavitation growth of the bubble. The most significant amplification and, consequently, the maximum tangential stresses in the shell are achieved using low-frequency (approximately 20 kHz) ultrasound and a thin shell. It is shown that, in the presence of a cavitation bubble, the mechanical stresses in the shell are many times greater than in a capsule filled with liquid alone.

The wave flow of a viscous liquid film along the lower surface of an inclined plane is investigated. Flow regimes with steadily traveling waves are identified, and their stability with respect to periodic linear perturbations with the same wavelength as in the nonlinear solution is examined. Calculations are performed using the full Navier-Stokes equations. Bifurcation lines are calculated for various inclination angles and Kapitsa numbers. Their structure is found to depend strongly on the Kapitsa number and only weakly on the inclination angle. At large inclination angles, a change in the bifurcation type from the wave-free solution occurs, and the film thickness vanishes at a certain distance from the bifurcation point. The critical angle at which film detachment occurs is determined as a function of the Kapitsa and Reynolds numbers.

An experimental study of the gas-droplet flow parameters was conducted in a small climatic wind tunnel at the ITAM SB RAS. The droplet size distribution of the liquid phase in the test section was determined using the PolisSpray optical shadowgraphy system. Shadowgraph images of droplets were obtained in various regions of the test section. An algorithm for droplet detection, based on a combination of gradient analysis and morphological operations, was developed and implemented to improve the accuracy of droplet size estimation. Droplet diameter distributions were obtained for the investigated regions of the test section and subsequently corrected for the effects of depth of field and optical blur. These parameters were estimated from the intensity gradient at the droplet image boundaries. The results were compared with those obtained using a Malvern Spraytec laser diffraction analyzer.

Results of numerical simulations of blood pumping through an elastic vessel using the vibro-volumetric method are presented. The simulations characterize blood motion in the vessel under vibro-volumetric actuation. It is shown that blood flow depends significantly on the frequency and amplitude of the driving force, as well as on the opening angle of the channel formed by the walls of the vibrating device. A qualitative analysis of the problem demonstrates the existence of a steady-state regime of blood transport along the vessel under the action of the vibrational force, with transport velocities characteristic of various perfusion pump designs. The influence of the key operating parameters of the device on the blood transport velocity is established, enabling flow rate control by varying the external excitation frequency for a given channel opening angle and driving force amplitude. The obtained dependences confirm the feasibility of perfusion and flow rate control of blood and blood-substitute solutions by adjusting the design and operating parameters of the device. A direction for further model improvement through optimization of the channel wall geometry is proposed.

The characteristics of supersonic flow in a converging rectangular channel are numerically investigated as functions of the channel aspect ratio and wall temperature. The channel consists of a converging inlet followed by a constant-cross-section region. In the inlet, a compression wedge with an angle δ _w = 13° generates a shock wave that induces boundary layer separation. Using the Navier-Stokes equations and the k-ω SST turbulence model, data on the flow structure and the characteristics of the separation zones are obtained at a Mach number M = 4.5 at the channel inlet.

Three-dimensional unsteady numerical simulations of conjugate heat transfer in the gas-dynamic path of a short-duration wind tunnel are performed to assess the effect of heat losses on the airflow parameters. The contributions of individual path components to the stagnation temperature drop are analyzed, and the influence of the thermophysical properties of the throttling unit material is investigated. The results demonstrate the decisive role of the throttling unit material in heat losses and substantiate the need for thermally insulating throttling elements to maximize the reproducible stagnation parameters of the airflow.

Data on the seeding particle distribution in the flow of a supersonic wind tunnel with electric-arc heating of the working gas are presented. The application of statistical approaches based on gray-level co-occurrence matrices (GLCM) to identify textural features corresponding to different boundary-layer flow regimes is discussed.

Experimental and computational data on the icing of a 300-mm-chord airfoil at freestream temperatures of -5 and -15 °C are compared. It is found that, at low Reynolds numbers, classical models do adequately reproduce the overall ice shape, but fail to resolve small-scale features (e.g., ridges, needles, and rivulets). The smoothing of these features is particularly pronounced for mixed-phase icing. For small unmanned aerial vehicles, this limitation is critical because small-scale ice on thin leading edges significantly alters the flow structure and heat transfer. The study demonstrates that ignoring small-scale ice structures makes it impossible to accurately predict the icing process, which calls into question the applicability of existing numerical models for analyzing the unmanned aerial vehicle icing.

Results of measurements of wall pressure fluctuations generated during the interaction of a supersonic underexpanded jet (with microjets at its nozzle exit) with an obstacle containing a coaxial orifice are presented. It is found that, within a certain range of linear parameters, microjet injection into the main supersonic jet reduces the amplitude of self-sustained oscillations caused by acoustic feedback between the nozzle and the obstacle. Outside this range, however, the presence of microjets does not significantly reduce the pressure fluctuations near the nozzle exit caused by periodic variations in the gas mass flow rate through the central orifice.

A computational framework based on the smoothed particle hydrodynamics (SPH) method for simulating the motion of multi-link fish-like bodies is presented and validated. The framework couples SPH with a multibody dynamics approach to solve the hydroelasticity problem (fluid-structure interaction) for fish-like swimmers. The solver is thoroughly verified against three benchmark problems. Comparison with published numerical results demonstrates that the proposed framework is capable of reproducing the key hydrodynamic features, including reverse Kármán vortex streets, thrust generation mechanisms, and motion-dependent performance characteristics. The developed and validated framework provides a computationally efficient tool for the design, control, and optimization of bio-inspired underwater vehicles.

The effect of a vertical AC electric field on a layer of a dielectric viscoelastic Navier-Stokes-Voigt fluid, salted from below and heated either from below or from above, is investigated using linear stability theory. The eigenvalue problem is solved exactly for stress-free boundary conditions, while the Galerkin method is employed for rigid boundaries. A numerical analysis of the influence of the electric field on the system is performed for both stationary and oscillatory convection modes. It is found that stationary convection occurs at low values of the concentration Rayleigh number, while a transition to oscillatory convection takes place at higher values. The Navier-Stokes-Voigt parameter plays a significant role in stabilizing the onset of oscillatory convection. The system is shown to be more stable when heated from above than when heated from below. The results obtained are in good agreement with available data in the literature.

A three-dimensional mathematical model for the propagation of a spontaneous hydraulic fracture in a poroelastic medium is presented, accounting for the prestressed state induced by a pre-existing propped fracture. The indicator curve behavior for an injection well experiencing spontaneous hydraulic fracturing is analyzed, and a physical interpretation of its characteristics is provided. A step-rate injection test is simulated, and the effects of the impermeable caprock thickness and the prestress due to the propped fracture on the indicator curve shape and fracture initiation pressure are evaluated. The slope of the indicator curve beyond the fracture initiation point is found to depend significantly on the fracture length and conductivity, as well as on poroelastic effects. In particular, increasing caprock thickness is revealed to raise the fracture initiation pressure due to additional stresses generated by elevated pore pressure-an effect that cannot be captured by two-dimensional models without further modifications. The simulation results demonstrate the sensitivity of the fracture initiation pressure to changes in reservoir pressure and confirm the need to account for three-dimensional poroelastic effects and prestress in the engineering design of waterflooding systems.

A mathematical model of real-gas flow to a vertical well in a fractured-porous reservoir is proposed, incorporating the pressure dependence of fracture porosity and permeability. The behavior of the bottomhole pressure and its time derivative is analyzed as a function of various formation parameters. A method for interpreting gas-dynamic well test data in fractured-porous reservoirs is developed, accounting for the pressure dependence of fracture permeability within the framework of inverse problem theory. Test calculation results are presented.

A two-dimensional problem of water-wave scattering by a completely submerged thin vertical porous barrier in the ocean is considered. The fluid is assumed to be bounded above by a free surface and below by a permeable seabed. Using Green’s integral theorem, the boundary-value problem is reduced to a hypersingular integral equation of the second kind expressed in terms of the potential difference across the plate. The equation is solved numerically using a collocation method with a finite series of Chebyshev polynomials of the second kind. The reflection and transmission coefficients are obtained as integrals involving the potential difference. The energy dissipated by the porous plate is also evaluated. Numerical results for the coefficients are presented, and the corresponding energy identity is verified. A significant effect of dual porosity is observed.

A mathematical model of conjugate heat transfer and a numerical method for estimating the temperature distribution in a model electronic unit of an unmanned aerial system filled with hydrogen and exposed to external airflow are presented. The three-dimensional mathematical model for the external aerodynamics and internal gas dynamics is based on the Reynolds-averaged Navier-Stokes equations, closed by the ideal-gas equation of state (for both air and hydrogen), the SST turbulence model, and appropriate initial and boundary conditions. The thermal state of the unit is described by the heat conduction equation. The two problems are solved in a coupled manner, thereby implementing a conjugate heat-transfer model between the external air and the internal hydrogen through the solid walls, whose thermophysical properties (heat capacity, thermal conductivity, and density) are specified as functions of temperature. The heat dissipation from the circuit boards of the model electronic unit is prescribed as a thermal boundary condition on the surfaces of the heat-generating components. Temperature distributions in various cross sections of the structure are obtained.

The linear stability of a combination of two mutually perpendicular flows in an inclined plane layer is investigated: a convective flow driven by a transverse temperature difference and a plane Poiseuille flow induced by a horizontal pressure gradient. Stability regime maps are constructed in the Reynolds number-Grashof number plane for various layer inclination angles, as well as disturbance regime maps in the inclination angle-Reynolds number plane. When the temperature of the upper boundary of the layer exceeds that of the lower boundary, the combined flow can be stabilized at Reynolds numbers higher than the critical Reynolds number for the plane Poiseuille flow without thermal stratification.

For a power-law temperature dependence of the viscosity coefficient, the problem of steady Poiseuille flow in a channel with nonuniformly heated walls is reduced to a three-parameter boundary-value problem for a system of third-order ordinary differential equations. In the absence of a pressure drop, the problem admits a solution describing the temperature distribution in a fluid at rest. This solution exists over a finite interval between the negative and positive critical values of the dimensionless temperature gradient at the channel walls. At small values of the Péclet number (based on the pressure drop), the first solution branch bifurcates from the quiescent state. Two additional branches are found when the wall temperature gradient exceeds the critical values. Thus, in the region of negative gradients, two solutions exist for the same parameter values, differing in flow rate and wall heat flux. For wall temperature gradients exceeding the positive critical value, the third branch is a continuation of the first. A distinctive feature of the second and third branches is that, as the Péclet number tends to zero, the flow rate tends to a nonzero value.

A new approach to measuring the local heat transfer coefficient during condensation of saturated water vapor on the surface of a horizontal pipe is proposed. The heat transfer coefficient values are determined from direct measurements of the heat flux density using gradient heat flux thermometry and of the pipe surface temperature using thermocouples. Results are presented for a test section supplied with saturated water vapor at a temperature close to 100 °C and a flow rate varying from 4 to 10 kg/h; the cooling water flow rate was 130 kg/h. Angular distributions of temperature, heat flux density, and heat transfer coefficient during condensation are constructed. Depending on the vapor flow rate, either mixed or film condensation is found to develop on the surface. The proposed approach provides a relative uncertainty in the local heat transfer coefficient of less than 8 %.

This paper describes a modification of the Sieverts method for measuring hydrogen absorption and desorption isotherms (PCT isotherms) for a sample of an AB₅-type intermetallic compound with the composition LaNi_4.8Al_0.2. The modification consists in performing measurements by stepwise changing the temperature of the working vessel containing the sample at a fixed hydrogen concentration, rather than by adding or removing discrete hydrogen portions at a constant temperature. Hydrogen absorption and desorption isotherms obtained by the classical and modified methods for the same sample are compared. The modified Sieverts method is shown to be more accurate than the classical version, due to the elimination of cumulative measurement error.

A numerical model of spinodal decomposition of a thermally unstable, partially miscible liquid under pulsed heating is developed. The model is based on a system of differential equations describing heat and mass transfer. Simulations are performed over time intervals of up to 40 ms. When a cylindrical probe is heated, the surrounding liquid separates into two immiscible phases. Due to the surface tension gradient (Marangoni effect), droplets of these phases move both toward and away from the probe, leading to a significant enhancement of heat transfer. The resulting time-dependent probe power and the relative change in the heat transfer coefficient are in good agreement with experimental data obtained from pulsed heating of an aqueous PPG-425 solution.

A physical and mathematical model of ice accretion on an axisymmetric body rotating in an airflow containing ice particles with various sphericities is proposed. Upon impact with the surface, a portion of the particle mass is deposited. A numerical study is performed to determine the ice shape, accounting for possible detachment by centrifugal force. The effects of viscosity and turbulence of the carrier gas on the processes under consideration are taken into account.

The problem of verifying computational results for liquid-metal coolant flow in nuclear reactor fuel assemblies with spacer grids is addressed. The verification results demonstrate that the CADFlo software package provides high accuracy in simulating both laminar and fully developed turbulent flows. For heat transfer problems involving liquid-metal coolants in fuel assemblies, good agreement is obtained between the computed temperature distributions and hydraulic resistance coefficients and the experimental data.

Wave reflection in a nonlocal biothermoelastic medium described by a hyperbolic two-temperature model is investigated within the framework of the refined Lord-Shulman model. A two-dimensional half-space with impedance-type boundary conditions is considered. The governing equations are reduced to dimensionless form and solved using potential functions. The existence of three longitudinal waves and one transverse wave is demonstrated. Reflection coefficients and the corresponding energy ratios are obtained. The refined Lord-Shulman model is compared with the classical model. Although the plane-wave reflection problem is idealized, it provides a useful theoretical basis for studying the influence of biological tissue parameters on the energy of reflected waves.

An experimental study of plastic strain localization during static uniaxial tensile testing of steel specimens with asymmetric edge stress concentrators is performed. The study employs modern thermal imaging equipment capable of recording the temporal evolution of temperature fields during deformation. The proposed experimental methodology, based on infrared thermography, is shown to be applicable for investigating the kinetics of elastoplastic deformation and for determining the ultimate state of the material in the stress concentration zone.

The synthesis of a composite material based on the metal hydride alloy TiFe_0.85Mn_0.05 and ABS polymer is presented. The thermal properties of the samples are studied using thermogravimetric analysis and differential scanning calorimetry. The morphology of the composite material is examined by scanning electron microscopy. The effect of the polymer on the hydrogen sorption characteristics of the intermetallic compound TiFe_0.85Mn_0.05 is investigated. The maximum hydrogen mass fraction in the synthesized composite material is found to be 1.3 % at a temperature of 30 °C and a pressure of 30 atm.

A method for enhancing the corner strength of thin-walled square tubes by incorporating four corner reinforcements consisting of stiffeners with or without lightweight polyurethane foam fillers is proposed and validated. Three-point bending tests of thin-walled square tubes with corner reinforcement are simulated using the ABAQUS/Explicit software package. The numerical results show that corner reinforcement significantly changes the cross-sectional deformation mode of the tubes. The specific energy absorption of tubes with corner reinforcements is substantially higher than that of unreinforced tubes. Based on an analysis of the cross-sectional deformation, it is proposed to remove the two lower corner reinforcements to further increase the specific energy absorption. The specific energy absorption of a tube reinforced with only the two upper corner reinforcements is 2.24 times higher than that of a conventional hollow square tube and also exceeds that of the proposed configurations with four reinforcements.