Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2021 number 2

Results of experimental and numerical investigations of a supersonic flow of cylindrical models aligned at a zero angle of attack with frontal inserts made of cellular-porous nickel are reported. The experiments are performed in a supersonic wind tunnel at Mach numbers M¥= 4.85 and 7.00 and unit Reynolds numbers Re1 = 2.7 x 106 and 1.5 x 106 m-1, respectively. Numerical simulations with the use of a ring-shaped skeleton model of the porous material are also performed. A possibility of drag control is studied for two thermal methods: external heating of the porous insert and internal heating of the insert by a glow discharge. The mechanisms of the thermal action and the efficiency of the thermal methods of drag control are analyzed.

Results of experimental and numerical investigations of walls reinforced with steel fibered concrete panels are reported. Eighteen walls produced by using hollow bricks and aerated concrete are studied in experiments; these walls are strengthened with concrete panels produced by using steel fibers at certain ratios. Six unreinforced reference specimens are also tested. Load-displacement curves are derived, the maximum stresses and displacements are determined, and the cracking process is studied. The experimental results are compared with those obtained from modeling.

A problem related to the plane-parallel steady motion of a low-viscosity incompressible fluid that fills half a rotating cylindrical cavity is under consideration. The Navier slip condition is imposed on the fluid - solid wall interface, and the condition for the absence of tangential stresses is imposed on the free boundary. The equation of the boundary layer considered on the entire boundary of the semicircle as a whole is reduced to a heat conduction equation by changing the variable. The solution to the problem is constructed in the form of a series, while the corner boundary layers are ignored. Calculations and comparisons with the solution built earlier using the finite difference method are performed.

This paper presents a model that links the polymorphic transformation of a crystalline substance under shock-wave loading with a change in its elastic energy. The complete and partial transformation of the substance in the shock front and the conditions for the occurrence of this transformation are determined. The model was tested by describing polymorphic transition in non-porous pyrolytic graphite and transitions in the silicon dioxide system. It is shown that the model satisfactorily describes available experimental results.

This paper presents the results of experimental determination of electrophysical characteristics such as the permittivity and dielectric loss tangent of plasticized three-dimensionally cross-linked and filled with solid dispersed fillers of polymer composite material on based on low molecular weight rubbers. The measurement technique is described and the experimental results are analyzed. The dependence of the thermal energy density absorbed by the investigated material on the time of exposure to ultrahigh-frequency radiation is calculated.

An experimental study of a novel dryer is performed. In this current study, paddy drying is carried out using a vertical dryer. The paddy mass is varied as 10, 20, and 30 kg at the air temperature and velocity of 60oC and 5 m/s, respectively. The results indicate that an increase in the paddy mass raises the drying rate and efficiency. However, the large masses of paddy need a long time to reach the required 14% moisture content. The highest efficiency achieved is 3.27% at the paddy mass of 30 kg.

Natural vibrations of a rectangular plate with two pinched and two freely supported edges. The Bubnov method - Galerkin methods are used to obtain the first eigenvalues, and one of the test functions has its first eigenvalue calculated with an error smaller than 1%. Comparison with known results is carried out, with eigenforms given.

Within the framework of multiphase media mechanics, a mathematical model of gas mixture dynamics is obtained, including helium and water vapor, in a layer of resting composite sorbent based on microspheres and a porous matrix of moisture absorber made of aluminum oxide. The study is carried out with account for the law of conservation of momentum with account for the force of resistance to the layer, described by the Forchheimer filtration relations, and the law of conservation of energy within the framework of a single-temperature non-heat-conducting models.

Numerical simulation of dam-break water flow over a horizontal dry bottom was performed. Computational technologies including methods for determining the position of the interface and the continual model of the surface tension force implemented in PIFI code, and OpenFOAM software package with interFoam solver and various versions of the two-parameter (κ-ε)-model with adjustments made taking into account the behavior of flows in areas with small Reynolds numbers were modified and verified. Calculated integral characteristics of dam-break flow were analyzed and compared with measured data. It is shown that taking into account the surface tension and using an adequate turbulence model leads to deceleration of water movement and hence to a decrease in the speed of the wave front, resulting in better agreement between the results of calculations and laboratory experiments.

The possibility of using microvortex generator jets to improve the flight stability and firing accuracy of the M549 projectile by regulating the vortex distribution on the surface is studied in this paper. The microvortex generator jet is inserted in front of the projectile shoulder, and the flow field structure around the projectile is simulated by the detached eddy simulation method. The numerical results show that microvortex generator jets can eliminate irregular vibrations induced by aerodynamics forces by inhibiting vortex shedding.

Azimuthal gyroscopic waves in a floating liquid forming a centrifuged layer on the solid wall of a cylindrical rotor cavity are studied. The exact solution of the linearized hydrodynamic problem with a nonclassical boundary condition on the free surface is obtained. The dispersion equation is derived. The influence of the inertial surface of the liquid on stability of quasi-solid rotation of the centrifuged layer is studied.

According to the dynamic model of the vehicle starting process and the theory of heat transfer, a clutch temperature field model under different starting conditions is established based on the time-varying characteristics of the convective heat transfer coefficient of the flow field. The effects of the engine target speed, clutch engagement pressure change rate, and road gradient on the temperature field distribution are revealed. The results of the study are compared with those obtained earlier by the finite element method.

The flow of the Ellis fluid in the renal tubule is investigated in this paper. The fluid absorption at the wall is influenced by the pressure gradient across the wall and by the permeability of the wall. The governing equations are considerably simplified if the tubule radius is assumed to be much smaller than its length. Important quantities of interest are computed numerically. The results are compared with available data and are found to be in good agreement.

A problem of sedimentation-induced concentration convection in a spherical cavity is considered. It is shown, that the flow is formed due to concentration inhomogeneity near the surface and has the form of two tori, and the convection leads to acceleration separation of the mixture.

A problem of the flow around a rectangular wing under the transonic buffer conditions in a wind tunnel is investigated numerically and experimentally. It is shown that a three-dimensional flow with a “mushroom” structure of the surface streamlines on the wing surface is formed instead of a close-to-two-dimensional flow in the case with self-excited oscillations along the streamwise coordinate (buffet). For the purpose of buffet control, an ejector is proposed, which provides boundary layer suction from the upper surface of the wing and jet ejection at the trailing edge of the wing. The spectral analysis of the experimental pressure oscillations on the upper surface of the wing shows that the proposed device effectively suppresses pressure oscillations at the buffet frequency.

The paper considers the results of calculating non-stationary pressure and temperature fields in a low-permeable reservoir with a hydraulic fracturing crack, taking into account the thermodynamic (Joule-Thomson and adiabatic) effects. The influence of the crack parameters (width and permeability) on the nature of the time variation in the temperature of the fluid flowing into the well is analyzed. It is shown that an increase in the pressure gradient in the crack with decreasing crack width and permeability enhances the Joule-Thomson effect. As a consequence, the temperature of the flowing liquid increase over time and the adiabatic cooling effect begins to prevail with increasing width and permeability of the crack, resulting in decrease in the temperature of the supplied fluid. The obtained features of the temperature field can be used in the diagnostics of hydraulic fracture parameters.

The analysis of the burst failure of a thick-walled cylindrical pressure vessel with plastic anisotropy under the action of internal and external pressures is carried out. Theoretical solutions for the burst pressure and the corresponding equivalent strain for the thick-walled cylindrical pressure vessel with ends closed are derived. The effects of plastic anisotropy, strain hardening, and external pressure on burst failure are discussed. The results show that the burst pressures for close-ended thick-walled cylindrical pressure vessels are dependent upon plastic anisotropy and external pressure, while the corresponding equivalent strains are only dependent upon plastic anisotropy, and the degree of the dependence is related to the strain hardening exponent of the material and on the ratio of the outer radius to inner radius of the vessel.

This study touches upon a numerical simulation of vibrations of an elastic rod whose height is significantly greater than the transverse dimension and which is installed perpendicular to the external flow and rigidly fixed to the substrate. Modeling is performed in the ANSYS software complex using bi-directional technology pairing. Eigen-frequencies and vibrations modes of the rod are calculated. The structure is analyzed and the features of the flow are described. The process of excitation of vibrations of an elastic rod under the action of an external flow is investigated and its stress-strain state is determined. The vibration modes in the direction of the incident flow and in the transverse direction are determined. It is shown that at close values of the first natural frequency and the frequency of vortices descent, the amplitude of the rod oscillations in the transverse direction sharply increases to a value approximately equal to 0.06 of the rod height, after which a self-oscillating mode is established with a constant amplitude in the transverse direction and variable amplitude in the direction of the incident flow.

The damage to a railway during high-speed movement of heavy trains in its various sections is modeled using a grid-characteristic method in the case of structured grids the damage process. The separation of sleepers from the ballast layer is studied. Computer simulation provided various wave patterns and patterns of dynamic distributions of the Cauchy stress tensor (pressure) components during train movement on a railway track. The cracking process is described.