Journal of Applied Mechanics and Technical Physics最新文献

I have studied the effect of the Reynolds number, static pressure, and flow temperature on vortex structures in the turbulent wake behind a circular Teflon cylinder. Velocity fields have been measured by the PIV method in a water channel at Reynolds numbers from 1.75 × 10⁵ through 2.84 × 10⁵. The drag coefficient of the cylinder, as well as average wake characteristics, has been found to point to an earlier drag crisis, corresponding to rough nonhydrophobic surfaces. Reducing the oncoming flow pressure has been shown to cause an increase in the wake behind the cylinder and drag. In spite of the large wake characteristics, raising the flow temperature leads to a decrease in cylinder drag, which is attributable to the decrease in Reynolds stress on the cylinder surface and, accordingly, in friction drag.

We experimentally investigate the perforation of wire mesh screens by an aluminum projectile over a range of impact angles. The study focuses on the fragmentation mechanism driven by the penetration of mesh wires into the projectile material. A series of high-velocity impact tests on thin mesh screens reveal that, as shockwave-induced fragmentation diminishes and the impact angle increases, the projectile undergoes fragmentation primarily via the wire penetration mechanism. We assess the performance of a mesh screen as a protective layer at various impact angles, comparing its effectiveness to that of a solid barrier shield. Additionally, the ballistic characteristics of the resulting fragment cloud are evaluated.

This paper presents a numerical study of a submerged round jet at a low Reynolds number exposed to two sources of harmonic oscillations introduced at opposite lateral boundaries near the inlet. It is shown that, for a certain combination of forcing parameters, the flow splits into two branches, as in a number of other experiments and calculations in the presence of various types of acoustic and mechanical disturbances. Time-averaged flow velocity distributions are obtained. The influence of the oscillation amplitude on jet behavior is studied. A threshold amplitude above which flow splitting occurs is determined.

This paper examines the propagation of a shock wave pulse from gas to a porous medium saturated with a bubbly liquid and describes the process in the case of one-dimensional planar motion under the assumption that the skeleton of the porous medium exhibits viscoelastic behavior. We consider the dynamics of a shock pulse in a porous medium having a sandstone or loose sand skeleton and saturated with a gas–liquid mixture and analyze how parameters of the shock pulse and gas–liquid mixture influence the shock pulse dynamics.

This paper presents an experimental study of the focusing of internal waves emitted by horizontal oscillations of a torus-like body in linearly stratified fluid. The body had a circular generatrix and an elliptical backbone curve connecting the centers of the generatrices. Experimental data on the internal wave amplitude distribution in the vicinity of an axisymmetric oscillating torus are compared to linear theory estimates in the thin body approximation. It is shown that, if waves are generated by nonaxisymmetric wave generators, the amplitude in the focusing zone is smaller, which is caused by differences in both total emission power and focusing zone structure. We have constructed isosurfaces of experimentally measured wave amplitudes in the focusing zone and compared the data to ray theory predictions.

For a macroscopic model of a two-velocity two-temperature mixture of gas and dispersed particles, we have obtained a partial solution to a system of partial differential equations in the form of a monochromatic acoustic wave. The mixture has been modeled as interpenetrating continua with relaxation terms describing momentum and thermal energy transfer between the dispersed and carrier phases. The partial solution has been found by the Fourier method and can be used as a verification test for numerical models of gas dispersion media. At arbitrary velocity and thermal relaxation times, to generate a solution one should numerically find complex roots of the dispersion relation, a sixth-degree polynomial. In the case of infinitely short velocity and thermal relaxation times (relaxation equilibrium that is obtained in simulation of ultrafine mixtures), a reference solution has the form of a traveling wave whose velocity is equal to the effective speed of sound in the gas–dust medium. The effective speed of sound has been shown to be sensitive to parameters determining heat transfer processes. We have presented a publicly available code that generates a partial solution for arbitrary problem parameters.

This paper investigates a line-drive waterflood pattern with two injection wells, between which a hydraulic fracture spontaneously propagates. Using a simplified model implemented in the RN-KIM hydrodynamic simulator, we consider a scenario where propped fractures from the two injectors connect to form a single dominant hydraulic fracture. We model the propagation of an induced fracture between two wells with existing propped fractures and analyze how the difference in wellhead injection pressures affects the injection rate in each well. The results demonstrate that an injection pressure difference between adjacent wells can cause a severalfold decrease in the injection rate or even a complete well shut-in. This occurs when the well with the higher bottomhole pressure “dominates” the flow within the high-conductivity fracture. Furthermore, we analyze the impact of the operating conditions of adjacent injectors and the geomechanical properties of the reservoir on the injection rate.

The distributed receptivity of a swept-wing laminar boundary layer to unsteady free-stream vortices with a streamwise-oriented vorticity vector in the presence of spanwise-uniform surface roughness has been investigated experimentally. The experiments were performed on a 25-degree swept-wing model under fully controlled disturbance conditions. It has been found that unsteady streamwise flow vortices can lead to very efficient streamwise-distributed excitation of unsteady cross-flow instability modes at combination spanwise wavenumbers due to vortex scattering on surface roughness. This paper (Part 1 of the study) describes the experimental approach and its theoretical justification, the base-flow structure, experimental evidence for the high efficiency of the receptivity mechanism, and the experimental confirmation and importance of streamwise wavenumber resonance. Part 2 of this study is devoted to the experimental estimation of the amplitudes and phases of distributed vortex-roughness receptivity coefficients as functions of the disturbance frequency and spanwise wavenumber. It also presents the receptivity coefficients responsible for the excitation of cross-flow waves on a smooth surface and provides a comparison of the relative efficiency of these two mechanisms.

This paper presents a numerical study of the stress–strain state of a nonspherical shell under pulsed loading. The influence of the height-to-radius ratios of elliptical bottoms on the maximum stresses in explosion-chamber shells is investigated. The dependence of the stress–strain state at the pole of the shell on the height of the bottom is examined. The use of elliptical bottoms of optimal height is shown to reduce the stress concentration.

To study inherent features of coating growth by the cold spraying method, we have constructed a continual physico-mathematical model which takes into account the possibility of collisions of particles of the material being deposited with the substrate (coating) surface at various angles. Calculation of coating formation on a substrate with a wavy surface profile at a constant nozzle velocity has shown that there are different deposition conditions on descending and ascending parts of the substrate surface. Calculations taking into account a nozzle tilt forward and backward with respect to the direction of its motion have demonstrated that there is an optimal tilt angle which ensures the largest coating thickness (the highest deposition efficiency).