Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2026 number 1

The effect of a gas curtain, formed by the destruction products of thermal protection elements in the combustion chambers of solid-propellant gas generators, on the material degradation of critical-section liners is investigated. Experimental data from two series of fire tests conducted on test benches are analyzed: one series performed by the authors and another reported in the literature. Both test series yield relatively low linear material loss rates, measuring 2.5 and 6 times lower, respectively, than those calculated using methods for large-scale solid-propellant rocket motors. A mathematical model is proposed based on the coupled solution to integral momentum and energy equations for the boundary layer and on the determination of the thermal state and failure of materials. This model allows for the introduction of additional admixtures of a cold gas, which is chemically inert with respect to carbon, into the fuel combustion product flow. The applicability of the model is validated by comparing simulation results with experimental data, with discrepancies not exceeding 5%.

The kinetic physical-mathematical theory of metal creep, which accounts for thermally activated dislocation glide, is applied to describe the creep process under uniaxial tension for the EI696 steel and the EI826 nickel alloy under non-stationary thermomechanical loading conditions. The new results obtained in this work demonstrate the potential of this theory for applications in aircraft design.

The fabrication of Al-metallic glass (Fe₆₆Cr₁₀Nb₅B₁₉) composites with low residual porosity and varying component concentrations is presented. During sintering, no interfacial interactions between the composite components are observed. The hardness and thermal conductivity of the Al-metallic glass composites are experimentally determined. The experimental data are compared with values calculated using the rule of mixtures. The measured thermal conductivity of composites containing 20 and 80 vol.% metallic glass closely matches values predicted by models for parallel and series phase connectivity, respectively. The hardness values for these composites are consistent with those calculated using the Reuss and Voigt models.

An experimental setup for free circular rotation of blunt bodies about their longitudinal axis is described. A procedure for determining the roll moment in wind tunnel tests is presented. A method for determining the equivalent aerodynamic roll damping coefficient is developed, based on the fact that the viscous friction moment component in rolling bearings is independent of the axial load. For a segmental-conical body, the experimental value of the coefficient is shown to be close to the value calculated by numerical integration of the continuum equations in a quasi-stationary approximation. The proposed method can be used to determine the roll damping moment of reentry vehicles, which is necessary for solving flight dynamics problems.

Results of a combined computational and experimental study of the vortex structure in the reattachment region of a separated flow at a freestream Mach number M_∞ = 6 are presented. Three compression corner configurations are examined: a compression corner formed by two flat surfaces, the same compression corner with sidewalls, and an axisymmetric model. The compression angle is identical in all cases, equal to 30°. The model geometry is found to significantly affect the structure and parameters of the vortex flow in the reattachment region. This specifically pertains to the presence or absence of longitudinal Görtler-type wall vortices, their geometric dimensions, and the magnitude of the force and thermal parameters in this region.

The distributed receptivity of a swept-wing laminar boundary layer to unsteady freestream vortices with a longitudinally oriented vorticity vector in the presence of uniform spanwise surface undulations is experimentally investigated. Experiments are performed on a 25° swept-wing model under fully controlled disturbance conditions. Unsteady longitudinal freestream vortices are found to induce highly efficient distributed (in the streamwise direction) excitation of unsteady cross-flow instability modes at combination spanwise wavenumbers. This excitation results from vortex scattering by surface inhomogeneities. Part 1 of this study (published in the previous issue of the journal) describes the experimental approach and its theoretical justification; the experimental setup; the mean flow structure; the method of disturbance generation; the characteristics of freestream and surface disturbances; experimental evidence for the high efficiency of the investigated receptivity mechanism; the important role of longitudinal wavenumber resonance in exciting the most amplified cross-flow instability modes. Part 2 of this study (the present paper) presents the experimental determination of the amplitudes and phases of the distributed vortex-roughness receptivity coefficients as functions of disturbance frequency and spanwise wavenumber. Receptivity coefficients responsible for cross-flow wave excitation on a smooth surface are also obtained, and the relative efficiencies of the distributed vortex receptivity and vortex-roughness receptivity mechanisms are compared. The results are further compared with those previously reported for distributed vortex receptivity on a smooth surface.

The feasibility of controlling turbulent incompressible flow over an asymmetric Clark Z airfoil is investigated using two passive techniques. Firstly, air bypass through perforated surface regions from a high-pressure to a low-pressure area. Secondly, an external pressure flow introduced through the leading edge of a wing and subsequently diverted to its lower surface. The study is conducted over a chord within a Reynolds number range Re_c = (0.40-1.28) × 10⁶ and angles of attack from -6° to 6°. The examined control method exhibits an ambiguous effect, which depends significantly on the length and chordwise position of the mass-transfer region, the angle of attack, and the Reynolds number. Under certain conditions, however, a reduction in airfoil drag of 4-5% and an increase in lift are achieved, leading to an improvement in aerodynamic efficiency.

Results of the first combined computational and theoretical study of the effect of flow-aligned rectangular depressions (slots) on the surface of a flat plate on boundary-layer stability at a freestream Mach number M_∞ = 2 are presented. Slots of various depths (Reynolds number 0 ≤ Re_h ≤ 5400) and small width relative to the instability wavelength are considered. The mean flow is obtained using the FlowVision computational fluid dynamics package. Linear stability theory calculations reveal that increasing slot depth shifts the frequency range of boundary-layer instability toward higher frequencies. The spatial growth rates of the disturbances become lower than those for a boundary layer over a smooth surface, indicating flow stabilization.

The mechanism of longitudinal vortex formation in a supersonic jet issuing from an axisymmetric radial nozzle is investigated. Numerical simulations of the gas flow reveal that these vortices arise when gas flows from the prechamber into the inlet channel through a series of holes in a direction perpendicular to the axis of symmetry of the radial nozzle. The resulting vortices are then transported by the gas flow from the inlet channel into the radial nozzle and subsequently into the supersonic jet emanating from the nozzle. The numerical results are in satisfactory agreement with experimental data.

An original method for constructing a model porous medium is proposed. The approach is based on a well-known and widely used capillary model that accounts for pore-size distribution. The porous medium model is constructed by dividing the medium into thin layers perpendicular to the assumed flow direction, with capillary segments whose characteristics are determined using standard core analysis methods. The layers are probabilistically interconnected, forming parallel capillaries with variable cross sections. Within the inertialess flow approximation, the effective diameter of the capillaries is calculated. A pair of connected capillaries of different diameters is then replaced by a new capillary with this effective diameter. After repeating this operation iteratively, the original porous medium is represented by a bundle of parallel capillaries of uniform diameter. The theoretical aspects of the method are described, the adopted assumptions are substantiated, and the limitations of the model's applicability are identified. Results of absolute permeability calculations for two rock samples are presented and compared with those obtained using the classical capillary model. The proposed model is shown to provide a more accurate match between calculated and experimental data.

A method for controlling aerosol dispersion by applying ultrasonic vibrations of varying intensity is theoretically substantiated. Depending on the frequency and intensity of the ultrasonic field, either particle coarsening or fragmentation can be induced in the gas-dispersed system. A mathematical model for the coagulation and fragmentation of aerosol droplets in an ultrasonic field is developed. For the first time, a coagulation-fragmentation criterion ( t_CF ), defined as the ratio of the characteristic times of these two processes, is proposed. An expression for the critical particle diameter at which the characteristic times are equal ( t_CF = 1) is derived.

The distributions of velocity fluctuations in a Hagen-Poiseuille flow are obtained experimentally for various Reynolds numbers and pipe diameters. The longitudinal velocity fluctuation distribution is found to peak on the axis and to be independent of the Reynolds number. As the Reynolds number increases, the turbulence intensity in the tube decreases, while the root-mean-square value of the fluctuations increases. Velocity fluctuations (less than 2%) in the Hagen-Poiseuille flow are shown to have virtually no effect on the jet outflow from long pipes.

Full Navier-Stokes equations are applied to identify two branches of viscous flow regimes in the form of steady traveling waves between two smooth surfaces. The existence domain of the new solutions is determined on the parameter plane (wavelength and Reynolds number), and the flow regimes corresponding to one of the branches are shown to be unstable. Stable regimes exist over a wide range of Reynolds numbers, starting from values significantly lower than the Reynolds number at which the linear stability of the base steady-state solution is lost. The main wave characteristics of the new-type solutions are calculated. Achieving these solutions requires a pressure drop substantially greater than that needed for the base steady-state solution, while also resulting in enhanced heat transfer from the walls.

A numerical study of the effect of a perturbation generated by a vortex-generator fin on the local flow structure and turbulence of a bubbly flow in a planar channel behind a backward-facing step is performed. An Eulerian approach is employed to describe the flow dynamics and heat and mass transfer in both the carrier gas and dispersed phases. The problem is solved using the Reynolds-averaged Navier-Stokes equations, modified to account for the presence of bubbles. The influence of air bubble concentration, initial bubble diameter, and vortex generator height on the turbulent flow structure and the length of the separation region is investigated. The presence of the vortex-generator fin induces a significant (twofold) increase in the turbulence level in both single-phase and two-phase bubbly separated flows. The fin is found to exert a substantial effect on turbulence in the separated flow, with the turbulence level increasing by up to 60%. The addition of bubbles reduces the recirculation zone length (by 60% for ∆/H = 1/3).

A model for coupled axial-torsional oscillations of a drill string in a borehole of arbitrary profile is proposed. A numerical solution scheme is developed. A comparative analysis of the simulation results and field test data is performed. The main factors influencing the onset of stick-slip oscillations are identified as the intrinsic specific energy of rock destruction and the rotor speed. Comparison of the calculated results with field measurements demonstrates the adequacy of the model, with an accuracy acceptable for practical applications.

Results of an experimental study on the acoustoelasticity arising from the propagation of ultrasonic Rayleigh surface waves in a field of static bending stresses are presented. For a St. 20 steel specimen, the acoustoelastic effect is shown to differ under compression and tension. A calibration curve is constructed for Rayleigh surface waves, enabling their use for monitoring bending stresses-a capability not possible with bulk wave probing.

A gravity-based hydrodynamic flow loop capable of generating both steady and unsteady flow conditions is presented. The setup achieves velocities up to 16 cm/s and pressure fluctuations in a range of 60-130 mmHg within the measurement zone, enabling hemodynamic studies of virtually any segment of the cardiovascular system. For the first time, flow rate control is achieved by varying the angle at the junction of the systolic and diastolic flow circuits of the loop. Independent control of the minimum and maximum pressure in the unsteady flow is also implemented.