Journal of Applied Mechanics and Technical Physics最新文献

An analytical (exact) solution of equations of a two-dimensional boundary layer of a non-Newtonian viscous fluid in the case with mass transfer is obtained with the use of the power-law Ostwald–Reiner model in a particular case with (n = 2) (dilatant fluid). It is noted that the apparent viscosity in this case is described by an expression that coincides with the equation for turbulent viscosity of a Newtonian fluid derived by the Prandtl mixing length model. For the particular case under consideration, it is found that there is an analogy between the flows of a non-Newtonian fluid and a Newtonian fluid with turbulent viscosity.

Modern approaches to visualization and automatic identification of separation regions of three-dimensional boundary layers are discussed. The corresponding algorithms are implemented within the framework of the original LOTRAN software package designed to predict the onset of a laminar-turbulent transition in boundary layers over small-curvature surfaces. Their work is demonstrated using two configurations: a swept wing and a prolate spheroid.

It is proposed to use a curvilinear triangular finite element with a small number of degrees of freedom to reduce the computational effort in the numerical solution of problems of nonlinear dynamics of shells using time-stepping integration. Compactness of the finite-element formulation is achieved by applying strain-tensor invariants. In this case, the natural strain components determined in the directions of three coordinate lines parallel to the sides of the element are used. Solutions describing large displacements, rotations, and buckling dynamics are given to demonstrate the capabilities of the proposed finite-element model.

The impact interaction of compound projectiles with thin metal targets is studied, and a method for evaluating the ballistic limit and residual velocity of the projectile is proposed. The compound cylindrical projectile consists of a deformable highly porous nose section and a rigid non-deformable tail section. The velocity of the projectile is considered in the range 200–850 m/s. The problem is solved numerically in a two-dimensional axisymmetric formulation. The motion of the medium is described using the Lagrange method. Calculation results are compared with experimental data. The results are shown to be in good agreement with the results of calculations using available analytical models and experimental data.

Distributions of the amplitude of controlled disturbances in space and time and their frequency-wave characteristics are obtained from experimental results on weakly nonlinear development of the wave train in the region of a stationary wake inside the boundary layer on a flat plate at the Mach number M = 2. A stationary streamwise disturbance is generated by a pair of weak oblique shock waves. Controlled disturbances are inserted into the flow by a local high-frequency glow discharge located inside the model. The development of controlled disturbances is analyzed on the basis of the linear theory of hydrodynamic stability. Typical resonant wave triplets are identified. It is found that flow inhomogeneity suppresses the mechanisms of interaction of controlled disturbances.

Effect of the main parameters of a nonlocal continuum model on stress concentration is studied when solving a problem of tension of a plate with an elliptical cut at its center, also known as the Kirsch problem. The effect of thermal expansion of the medium on the stress-strain state of the plate is described. The results obtained in this study are compared with the classical results. It is shown that there is an decrease in maximum stress and heat flux density, as well as a decrease in the strain in the stress concentration regions.

The dispersion, spatial propagation, and settling of aerosol particles generated by a pulsed method using the energy of high-energy materials have been studied. Such aerosols are produced to decontaminate harmful gas or aerosol formations. A mathematical description of the evolution of a decontaminating aerosol cloud is proposed, and the results of experiments on the dispersion of an aerosol of titanium oxide particles are presented.

This paper presents the results of calculations of liner implosion without the formation of shock waves under the influence of a current up to 70 MA and a magnetic field induction up to 20 MGs (magnetic pressure up to 16 Mbar) in devices with a disk explosive magnetic generator. It is shown that during deep implosion of two-layer Cu–W and Cu–Ta liners, the shockless pressure in tungsten and tantalum can reach 40 Mbar (hydrodynamic cumulation). The inner part of the liner, whose mass is more than 32% of its total mass, can remain in a dynamically strengthened solid state at a temperature of its copper skin layer up to 38 eV.

The dispersion of a single-component fluid (water) by a model simplex atomizer is studied in detail using the local time-shift method with a SpraySpy device and high-speed visualization. The mean size and velocity distributions of droplets are measured depending on the pressure drop for the atomizer. The spraying of two immiscible fluids (kerosene and water) supplied to the same atomizer is visualized by shadow photography. It was found that the two-component emulsion disintegrated almost instantaneously in close proximity to the atomizer outlet orifice, resulting in significant deformation of the spray cone.

The paper describes a methodology for the experimental study of a powerful heat release in a microsized probe immersed in a two-component solution with a lower critical solution temperature. Experimental data on superheating relative to the liquid–liquid spinodal and thermal impact on the stability of the system for a water–PPG-425 solution are presented. The following conclusion is made for a solution whose near-critical mass fraction of PPG-425 is 30%: despite the high density of the heat flux through the heater surface (9.2–13.7 MW/m²), its temperature stabilizes at a value exceeding the equilibrium temperature of the liquid–liquid system by approximately 150 K. It is shown that the heat exchange process is stable against changes in the heating parameters: the nature of heat transfer by the solution remains the same. It is revealed that the heat transfer coefficient is several times greater than the corresponding value obtained for water.