Home – Home – Jornals – Journal of Applied Mechanics and Technical Physics 2022 number 6

An equation of the dynamics of formation and radiation of a quasi-empty oscillating cylindrical cavity in a fluid is derived for the first time with due allowance for the changes in the velocity of sound and the volume fraction of cavitation nuclei. A dimensionless formulation of the problem is proposed and analyzed under the condition of identical pressures in the cavitation zone and inside the cylindrical cavity at its boundary. As a result, a dynamic relationship between the volume fraction (velocity of sound) in the cavitation zone and the radius of the cylindrical cavity is found.

A non-stationary electrohydrodynamic model has been developed to describe the behavior of a dielectric liquid film on the electrode surface in the surrounding gas. It has been shown that the action of an inhomogeneous electric field can lead to perforation of the film with the formation of new contact lines. The field inhomogeneity was created using a round insulating insert in the center of the lower electrode. The perforation process is determined by the electric field strength, film thickness, the radius of the non-conductive insert, and the contact angle between the liquid and the solid substrate.

In the present study, the effect of operating pressure on the flame response is investigated numerically, and the validity of atmospheric tests is examined. The results show that the flame shape significantly varies at atmospheric pressure, and the flame response to imposed pressure fluctuations is changed; therefore, atmospheric test stands are not reliable enough to study the combustion instability.

This paper presents a method for determining the gas-dynamic parameters of gas flow based on nonintrusive PIV measurements of the velocity field. The wake flow past a model single nozzle of an emergency escape rocket is considered for the normal transonic (Mach number is 0.85) flight mode of a launch vehicle with a manned spacecraft. The flow around the nozzle is simulated numerically using the RANS and LES methods. The results obtained by the proposed method are compared with numerical and experimental data.

Results of an experimental study of blood properties are reported. To approach the boundary conditions of blood biophysics in a real flow, the viscoelastic measurements are carried out on surfaces coated with a 10-nm thick fibrous layer composed of extracellular matrix protein. For native whole blood, a plateau of the shear elastic modulus as a function of frequency is observed. It is concluded that a slow flow of blood plasma close to the vessel wall can generate a stationary plasma layer that contributes to the functional width of surface layers in blood vessels. The shear stress term calculated from the wall shear rate and blood viscosity becomes imprecise if it does not include the existence of this intermediate layer.

A nanoscale calculation is performed for water permeation through the cell membrane in a human body, which is 7-8 nm thick and contains densely distributed nanopores with the radii ranging between 0.2 and 0.5 nm. The pressure drop and the critical power loss on a single nanopore for initiating the wall slippage are calculated. The wall slipping velocity is found to increase significantly with reduction of the pore radius and to increase linearly with an increase in the power loss on the pore. For no wall slippage, the water mass flow rate through the pore is significantly lower than the classical hydrodynamic flow theory calculation; however, it is much greater (by three to five orders of magnitude) than the classical hydrodynamic flow theory calculation in the case where the wall slippage occurs. This water flow enhancement is heavily dependent on the power loss on the pore.

The current study focuses on the influence of thermal boundary conditions, especially for a ribbed cooling channel with two intersecting ribs. Numerical studies are carried out for the Reynolds number of 30000 under two kinds of thermal boundary conditions, i.e., the constant wall temperature condition and the uniform heat flux condition. The local normalized Nusselt number distributions and area-averaged values are compared and further analyzed. The thermal boundary type and value both affect the heat transfer performance. The uniform heat flux condition always yields higher heat transfer than the constant wall temperature condition. A correlation for the wall-to-coolant temperature ratio is obtained and compared with previously published correlations.

The two-dimensional Green-Naghdi equations are investigated in the case of an uneven bottom topography. The function which determines the topography of the bottom and may depend on time is considered. A group classification of the equations under study with respect to the function describing the bottom topography is carried out using an algebraic approach.

Results of an experimental and numerical study of a supersonic flow around a cylinder with a gas-permeable cellular-porous frontal insert aligned at various angles of attack are reported. The experiments are performed in the T-327 wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences at the Mach number of 7 and Reynolds number of 1.5x106 m-1. The forces and moments are measured on models with diameters of 10.0, 14.5, 24.0, and 34.0 mm. The models are equipped with porous inserts whose length is equal to two diameters of the cylinder, the porosity value is 95%, and the pore diameters are 1, 2, 3, and 4 mm. The angle of attack is varied in the interval 0-25oC. The numerical simulations are performed by means of solving three-dimensional Reynolds-averaged Navier-Stokes equations with the use of the (k-ω)SST turbulent model and a toroidal skeleton model of the porous material. Based on generalization of experimental and numerical data for the normalized drag coefficient at various angles of attack, empirical dependences of this quantity on the similarity parameter including the ratio of the pore diameter to the cylinder diameter and the Mach number are derived.

Results of methodical activities on optimization of computations of the laminar-turbulent flow on various computational grids aimed at saving computational resources are reported. The study is performed on the basis of data calculated for a supersonic flow around a swept wing in a virtual wind tunnel with the use of the ANSYS Fluent CFD software with an additional package for determining the laminar-turbulent transition developed at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences on the basis of the e^N method.

A problem of rotation of a fluid layer bounded by a solid plane and a free surface parallel to this plane is considered. The fluid can be an ideal or a viscous fluid. Conditions for the existence of solutions of the corresponding problems for the Euler and Navier-Stokes equations on an infinite time interval are formulated. Examples of the numerical solution of the problem are presented.

For a non-linear parabolic reaction-diffusion system, solutions of the diffusion wave type are constructed and investigated. For the first time, the formulation of the problem is considered, which involves the assignment of non-coinciding zero fronts for various desired functions. A theorem on the existence and uniqueness of solutions in the form of series in the class of piecewise analytic functions is proved. To construct approximate solutions of the desired type, a step-by-step iterative algorithm based on the collocation method and expansion in radial basis functions is proposed. Calculations were performed, for the verification of the results of which segments of the series were used. A numerical analysis of the behavior of the constructed solutions was carried out.

The paper considers the mechanism of reducing the permeability of aqueous graphene suspension through the oil-saturated core compared to distilled water. Analysis of experimental data shows that an increase in permeability is due to the formation of corrugated films at the interface between two immiscible fluids during their mutual motion. The appearance of wavy surfaces is the result of Kelvin-Helmholtz instability at the grapheme-nanofluid-hydrocarbon interface. It is also shown that the occurrence of instability is possible only in the presence of a transition layer-graphene film.

Two nonlinear models are proposed that describe the formation and evolution of the mixing layer between two codirectional stratified fluid flows based on a three-layer flow representation in the long-wavelength approximation. The models are similar in structure, and in Boussinesq approximation, the equations of motion are written in a uniform way in the form of a system of inhomogeneous conservation laws. The speeds of propagation of perturbations are determined, and the concept of subcritical (supercritical) flow is formulated. Continuous and discontinuous solutions of the models are constructed. It is shown that for a sufficiently large difference between the velocities of codirectional flows, the stationary mixing layer expands monotonically and the maximum entrainment mode occurs. With a decrease in the initial difference in the velocities of the cocurrent flows, an oscillating stationary solution is obtained and the structure of the mixing layer becomes wavy. For one of the flow modes, the obtained solutions are compared with experimental data.

A problem of internal waves in a two-layer stratified fluid with a density that depends exponentially on the depth inside the layers and has a jump at the interface is considered. An equation for the second long-wavelength approximation is derived, which describes solitary waves. The spectral properties of the equations of small perturbations of a horizontal piecewise constant flow are studied and the possible mechanisms for the occurrence of shear instability of a stratified flow are characterized.

A technique for manufacturing a metal composite material from Ti64 titanium alloy reinforced with SiC ceramic fibers using surface laser cladding technology is proposed. The influence of the parameters of laser action on the shape of a single track is studied. The stability of the formed composite material under high-speed impact has been studied. It is shown that for a sample reinforced with ceramic fibers, the depth of the crater in the substrate is 37% less than for a sample made of Ti64 alloy.

A technique has been developed and a program has been created for numerical calculation by the smoothed particle hydrodynamics method of the process of deformation of an elastoplastic material in the axisymmetric case in the presence of contact boundaries and thermal conductivity of materials. With the help of this program, the problem of the collision of an aluminum particle with a titanium plate under conditions of cold gas-dynamic spraying is solved. It is shown that during a collision in the vicinity of the contact boundary between a particle obstacle, an aluminum particle is intensely heated up to temperatures of the order of 400oC. The calculated temperature is much lower than the melting temperature of aluminum. An explanation is proposed for the mechanism of the formation of a chemical bond between an aluminum particle and a titanium plate under conditions of cold gas-dynamic spraying due to the formation of an intermetallic compound in a hot layer near the contact boundary due to self-propagating high-temperature synthesis.

An engineering method is proposed for determining the oscillation amplitudes during vortex excitation, taking into account the dependence of the excitation force coefficient, the Strouhal number and the logarithmic decrement of oscillations on the oscillation amplitude of the structure, the distribution of the correlation of aerodynamic force pulsations along the length of the structure, and including the Eurocode method as a special case. It is shown that the developed technique, in contrast to the known ones, makes it possible to more reliably calculate the amplitudes of oscillations of span structures during vortex excitation.

Integral Fourier and Laplace transforms are used to numerically obtain an analytical solution to a quasistatic problem of thermoelasticity for a band with constant properties. Results of numerical calculations are presented.

Three-dimensional periodic contact problems on infinite straight chains of punches acting on the face of a transversally isotropic elastic layer, the other face of which is under conditions of a sliding embedment, are studied. The isotropy planes are parallel or perpendicular to the layer faces. To solve contact problems, the method of nonlinear boundary integral equations is used, which makes it possible to simultaneously determine the contact area and contact pressures. Calculations are performed for known transversally isotropic materials.

The structure of foam materials is analyzed. It is noted that foam materials under uniaxial tension and compression have different strain diagrams. A simplified physical model for a heteromodular foam material in the form of a steel ring is proposed. The model was tested on a Walter + Bai AG LFM-L-1 test machine. The deformation of the model was analyzed using the ANSYS Workbench software package taking into account the contact interaction between its elements. The calculation results were compared with experimental data.