No 3 (2023)

The results of experiments on the study of stability of the dome of a water bubble rising through a salt solution are presented. The experimental results are obtained using the PLIF method by recording the flow in the plane that coincides with the axis of symmetry of the bubble, The experiments demonstrate the possibility of the development of instability in the vicinity of the pole of the dome of such a bubble in accordance with the previously published results of computational simulation.

Particle image velocimetry (PIV) method has emerged as a powerful technique for electrohydrodynamic (EHD) flow field measurements. Based on a series of parallel field measurements along the blade electrode, we reconstruct the three-dimensional (3D) structure of EHD flows produced by an actuator in the blade-plane geometry. A non-uniform distribution of injection intensity and velocity is observed along the electrode. With the aid of slice plots from different views of 3D Cartesian, it is understood that the applied voltage, electrode spacing and the electrode surface or tip roughness exert a remarkable effect upon the structure of EHD jets. The findings of this investigation will complement the full view of the 3D structure of the jet and be of broad use to guide the selection of appropriate positions along the blade for profile plane studies.

The problems of oscillatory flow of a viscoelastic incompressible fluid in a plane channel are solved for a given harmonic oscillation of the fluid flow rate. The transfer function (amplitude–phase frequency response) is determined. Using this function, the effect of the acceleration oscillation frequency and the relaxation properties of fluid on the ratio of the tangential shear stress on channel wall to the velocity averaged over the channel cross-section (cross-sectional velocity) is determined. It is shown that the viscoelastic properties of fluid, as well as its acceleration, are the limiting factors for using the quasi-stationary approach. The found formulas for determining the transfer function for viscoelastic fluid flow in the case of non-stationary stream make it possible to determine the dissipations of mechanical energy in a non-stationary flow of the medium which are of importance for calculation of the control of hydraulic and pneumatic systems.

We present the results of an investigation of the boundary layer stability on a flat plate having a region of gas injection/suction normal to the wall at a large supersonic freestream Mach number. The laminar flow past a flat plate having a region of distributed injection/suction of fixed intensity is modeled numerically using the integration of Navier—Stokes equations. The unstable disturbances in the boundary layer distorted by injection/suction are analyzed within the framework of the linear stability theory and the ${{e}^{N}}$ method for compressible flows. High-frequency disturbances belonging to the plane second mode of the boundary layer, which are the most unstable at high velocities, are considered. It is shown that gas injection/suction leads to a nonmonotonic variation of disturbance growth rates with the appearance of stabilization/destabilization regions, as compared with the case in which injection/suction is absent.

The effect of the shape of a single bubble at the initial instant on the bubble rising dynamics in a viscous fluid at rest is studied. Elliptical bubbles with various compression ratios are considered. Mathematical simulation of the process is based on the volume of fluid method, which makes it possible to trace the evolution of the interface. The results of calculations of test problems are in adequate agreement with the data of other authors available in the literature. The shapes of the interfacial surface and the velocity and vorticity fields in the process of bubbles rising in the gravity field are obtained at the Reynolds number Re = 35 and the Bond numbers Bo = 10 and 125. The main attention is paid to the regime of unsteady motion. It is shown that the bubble rise velocity has one or two local maxima depending on the properties of the media. It is found that bubbles initially elongated vertically rise more rapidly than those elongated horizontally.

The results of laboratory studies of the features of processes of flow through a porous medium are given for a physical model of the porous medium obtained by sintering glass beads. The program for manufacturing physical models is described and the results of the efficiency of displacement of vaseline oil by various compositions are presented. Water, mineralized water, micellar solutions, nanofluids, and micellar solutions with addition of nanoparticles were considered as the displacement agents. Based on an analysis of images, curves of variation in the saturation of the model porous medium with vaseline oil in the process of its displacement by various compositions are obtained. The micellar solutions with addition of nanoparticles were shown to be the most effective oil displacement agents in comparison with other presented compositions.

The results of numerical study of relaxation processes in oxygen at high temperatures are presented. Collisions of particles (atoms and molecules) are described by the molecular dynamics methods based on trajectory calculations within the framework of classical mechanics. A complex of programs for calculating the relaxation processes in mixtures of high-temperature gases involving internal modes that describe rotational and vibrational motions in molecules and molecular dissociation and atomic recombination in the presence of a third body is described. The relaxation process is described with reference to variation in the parameters in a mixture of atomic and molecular oxygen with various initial temperatures of the translational and internal modes. The results of calculations of the structure of shock wave in oxygen with the maximum translational temperature on the front higher than 5000–11 000 K are given. The results obtained are compared with experimental data.