A numerical study was performed to investigate the effect of vibrational excitation and relaxation of sulfur hexafluoride (SF6) molecules on the gasdynamic structure and stability of high-speed microjets exhausting from axisymmetric sonic micronozzles with a diameter of 10–110 µm. Direct numerical simulation of gas flow was based on solving three-dimensional unsteady Navier–Stokes equations using a two-temperature model of relaxation flows. The studies were conducted over a wide range of Reynolds numbers determined by the diameter of the micronozzles. The vibrational relaxation of gas molecules was found to influence the modal composition and spectral characteristics of perturbations, as well as the length of the laminar region of microjets.
An Erratum to this paper has been published: https://doi.org/10.1134/S002189442602001X
This paper presents the results of a numerical simulation and stability analysis of the flow in a boundary layer on a plate with a surface microrelief. The microrelief consists of long slots (recesses) oriented at various angles relative to the incoming flow at a Mach number M = 2. The slots under consideration have a depth-based Reynolds number Reh ≈ 1000 and a width that is small compared to the instability wavelength. Numerical simulation is used to determine the specific features of the flow past a plate with inclined slots and to study the evolution of time-localized disturbances. A stability analysis of the flow is performed within the framework of linear theory, based on averaged profiles of the boundary layer parameters. The computational results show that the presence of inclined slots induces a crossflow in the boundary layer, which leads to an increase in the disturbance growth rates. The obtained data are in good agreement with experimental observations and explain the destabilizing effect of inclined slots on the boundary layer.
One-dimensional unsteady flows of an incompressible non-Newtonian viscoelastic fluid between parallel plates are considered using the Johnson–Segalman model with multiple relaxation times. A distinctive feature of the model under consideration is its hyperbolicity over a wide range of flow parameters. A general model of this type with n relaxation times (modes) is obtained, and a change of variables is made, allowing the model equations to be written in a conservative (divergent) form. A series of calculations of unsteady flows in various regimes is performed, showing the occurrence of the shear banding effect as the mean flow velocity increases. The wall shear stress versus shear rate relation and the flow rate versus pressure gradient relation were obtained for steady plane Couette and Poiseuille flows, respectively. The resulting curves were validated by comparison with several sets of experimental data. The structure of steady solutions exhibiting shear banding, obtained as a numerical limit of unsteady solutions, is investigated. A selection rule is formulated for steady-state solutions that are asymptotically attained in unsteady numerical simulations. The hysteresis phenomenon under cyclic changes in flow velocity is analyzed.
An experimental study of hydraulic fracturing in thick-walled concrete cylinders with a central hole is conducted using a high-pressure fluid test rig. The cylinders are made of sand-based concrete using GTs 50 alumina cement. Estimates of the ultimate pressure obtained from local and nonlocal failure criteria are compared with the experimental data. It is shown that satisfactory agreement between the calculated ultimate loads and the experimental failure data under a nonuniform stress field is achieved using nonlocal failure criteria.
The pressure field problem in an oil and gas reservoir with a hydraulic fracture connecting an injection well and a production well has been solved. The solution is developed in the Laplace–Carson image space using an asymptotic method. Analytical expressions for the pressure field in the fracture are obtained in a quasi-steady-state approximation. An approximate formula for calculating the fracture pressure field is proposed. Computational experiments were performed using numerical inversion algorithms and the derived analytical expressions. Spatiotemporal pressure distributions are plotted for realistic reservoir and fracture parameters. Based on an analysis of the calculation results, the regularities of pressure field formation in a reservoir with a hydraulic fracture are refined. A comparison of numerical calculations and analytical dependencies shows that the proposed analytical formula is sufficiently accurate for practical applications within a time frame comparable to the productive life of real oil and gas fields.
This paper presents the results of an experimental study of the deformation and fracture of nature-inspired cellular structures under high-velocity compression. Tests are conducted on specimens with Schwarz primitive structure with various volume fractions, as well as solid specimens. The specimens are fabricated from a polymer (polylactide) using 3D printing. An increase in ultimate strength and elastic modulus is observed with increasing deformation velocity at a constant volume fraction φ . Specific energy absorption values are determined for the cellular structures studied. It is confirmed that the Gibson–Ashby relation is valid for cellular structures under high-velocity loading conditions.
The paper presents experimental results for the penetration of polyconical penetrators made of EP637 steel into M400 concrete blocks and sandy soil. The critical velocity is determined by successive iterations in the range of impact velocities characteristic of the transition of the penetrator from an undamaged state (reduction in model length by less than 5
A VT-6–10 α + γ ) structure of the matrix is transformed to the ( α + β ) structure, β -Ti stabilizes, the concentration of secondary phases (TiB, TiC _1 - x , TiB2, V2B3) increases, and an α_2 -Ti3Al intermetallic compound is formed. Postheat treatment leads to an increase in microhardness (to HV_0.3 = 651 ) and wear resistance (the wear volume decreases by 7
Approaches to the topology optimization of composite lattice structures are explored to improve their weight efficiency when used in rocket and space technology. Traditional winding methods and promising technologies, such as continuous fiber 3D printing are considered, which enable the design of microlattice structures with thin ribs and biomimetic properties. The application of the SIMP method for continuum and discrete models is demonstrated for a spacecraft cylinder. A comparison of various lattice structures shows that when using the SIMP method, the mass of these structures is 18.5
This paper presents experimental results on the effect of impact energy on the residual compressive strength of high-endurance laminated carbon fiber composite specimens. To investigate how the level of impact-induced residual stresses affects the residual strength of the specimens, additional studies are conducted using electronic speckle interferometry combined with the probe hole drilling method. Residual stress values are determined in the midplane of the specimens at the impact zone boundaries. Scatter in the experimental data, caused by dispersed damage within the material structure, prevented establishing a correlation between residual stresses after an impact with an energy of 0–110 J and the residual strength of the specimens.
A pseudodirect numerical simulation of turbulent natural convection in a nonuniformly heated closed square cavity filled with air is performed. The velocity vector components are calculated using the high-order lattice Boltzmann method. The analysis of thermodynamic characteristics is carried out through a finite-difference solution of the macroscopic energy equation using a fourth-order Runge–Kutta scheme. The developed hybrid algorithm simulating the direct numerical simulation method is tested on benchmark problems of turbulent natural convection. Numerical studies are performed for Rayleigh numbers 10^10⩽R⩽10^11 . It is found that increasing R increases the intensity of thermal plume generation on isothermal walls and the region of turbulent vortex formation. Stagnation zones of the coolant were identified in the vicinity of the horizontal walls. It is shown that the distribution of second-order statistics, except for temperature variance, depends on the thermal plume configuration.
Integration in Lagrangian variables was performed for a submodel of steady-state ideal gas motions with constant pressure in the flow region. A general solution was obtained for the invariant submodel of stationary-type rotational isobaric motions. Examples of helical gas motions with constant pressure are considered.
The mechanical properties of a new diamane-reinforced copper composite were studied by molecular dynamics simulation. The Young’s modulus and tensile strength of the Cu–diamane composite were determined to be 117 and 16.4 GPa, respectively. These values can be increased by increasing the number of diamane layers in the composite.
This paper presents the results of experiments on fabricating a composite material based on PTS-1 titanium reinforced with a TiN phase at volume fractions of 4, 8, 12, 21 α -Ti and β -Ti phases and secondary δ -TiN and ε -Ti2N phases. An increase in the titanium nitride concentration induces a β↔α polymorphic transformation, forming an α -Ti–TiN eutectoid. Raising the sintering temperature increases the grain size of the titanium β -phase by 250
This paper presents the results of developing a concept for a vacuum aerodynamic facility based on the AT-303 vacuum wind tunnel at the Khristianovich Institute of Theoretical and Applied Mechanics, Siberian Branch of the Russian Academy of Sciences. The layout, geometry, design features, and advantages of the proposed facility are described. Estimates of its operating parameters and performance characteristics are provided.
This paper presents a computationally efficient ray-tracing boundary treatment for the lattice Boltzmann method, which accurately handles complex geometries using only discrete surface meshes, eliminating the need for analytical curvature descriptions. The key innovation is a robust geometric intersection algorithm that leverages ray-segment (2D) and ray-plane (3D) tests to precisely locate boundary points, requiring no pre-processing while maintaining second-order accuracy via the conventional bounce-back scheme. Validations—including 2D cylinders (Re = 100), NACA0012 airfoils (Re = 500), and 3D spheres—show exceptional agreement (≤3
An equilibrium equation for a thin isotropic nanoplate with boundary conditions is obtained using the nonlocal theory of microstructural deformation of thin plates. An approach is proposed to construct a solution to this equation for a rectangular nanoplate hinged at the ends using Chebyshev polynomials of the first kind and the collocation method. The deflection of the nanoplate midplane and the bending moments are analyzed as functions of a nonlocal nanoscale parameter.
The amplification of a shock-wave pulse transmitted through a sand layer is investigated as a function of layer thickness. It is shown that, as the thickness of the sand layer increases to a certain value, the amplitude of the probing pulse first increases and then decreases. The formation of pressure peaks occurs almost simultaneously throughout the entire sand layer.
An exact solution of the two-dimensional Wiener–Hopf integral equation is obtained for the first time and used to solve mixed problems in acute-angled wedge-shaped domains. Mixed problems for an arbitrary multilayer anisotropic composite are considered. The block element method is used in combination with topological and factorization approaches. The obtained solution has an integral representation that can be used in traditional software for integral evaluation when studying anisotropic composites. The solution contains singular sets in which it tends to infinity, which complicates direct numerical solution of such mixed problems. The exact solution of the two-dimensional Wiener–Hopf integral equation is equivalent to solving a mixed problem in a wedge-shaped domain with an angle of 90°. Using this result and topological methods allows the solution of these equations in arbitrary acute-angled wedge-shaped domains. A theory of contact problems for acute-angled wedge-shaped dies is constructed.
