Fluid Dynamics

Meshkov, E.; Mokretsov, R.; Smagin, I.

doi: 10.1134/S0015462819050070pmid: N/A

The technique of experimental investigation of the effect of an accelerated shear flow on the development of the Rayleigh—Taylor (RT) instability at the interface of two fluids at a small Atwood number is developed. Using a counterpart of the laser sheet method (laser induced fluorescence) the data on the structure of the RT mixing zone are obtained and the instability stabilization under the action of an accelerated shear flow is confirmed.

Khabibullin, I.; Khisamov, A.

doi: 10.1134/S0015462819050057pmid: N/A

At present, the hydraulic fracture technologies are widely used for intensification of oil and gas recovery from reservoirs with hard-to-recover reserves. The simulation of the processes of flow through porous reservoirs with hydraulic fractures is fairly completely developed in the steady-state flow approximation. Unsteady processes of pressure distribution are considered with reference to the theory of hydrodynamic methods of investigations of wells in which asymptotically limited intervals of variations in the coordinates and time, i.e., the distances of the order of the well radius and time much smaller than the characteristic time of the process of flow through the porous medium, are considered. At the same time, in the reservoirs with hard-to-recover reserves (low-permeability reservoirs and high-viscosity oils) the duration of the unsteady processes of pressure redistribution can be of the same order as the characteristic time of flow through the reservoir. In the present study new analytical solutions of the problem of unsteady pressure redistribution in the neighborhood of a well penetrated by a vertical fracture are given. The scientific novelty of the study consists in the fact that, firstly, the fluid compressibility in the fracture and, secondly, the fluid flow not only through the fracture but also through the porous reservoir are taken into account in the model used. The solutions of the problems are constructed using the Laplace transform technique. In particular cases, the expressions well-known in literature follow from the solutions obtained. The analytical solutions obtained which makes it possible to determine the main characteristic features of the processes of flow through a porous medium are analyzed.

Shefer, I.

doi: 10.1134/S0015462819040098pmid: N/A

The linear stability of combined evaporating liquid—vapor-gas mixture flow is investigated under conditions of inhomogeneous heating within the framework of the conjugate problem. The exact solution of the Navier-Stokes equations in the Boussinesq approximation is used to describe the two-layer flow. The solution takes into account the influence of both nonzero streamwise and transverse temperature gradients and the direct and inverse thermal diffusion effects in the vapor-gas layer and on the phase interface. The influence of the applied external thermal load on the main flow parameters, their structure, the volume vapor content, the mass evaporation rate, and the stability is studied for systems with various liquid-layer thicknesses. The typical forms of characteristic perturbations are distinguished and the critical loads that lead to loss of stability at small transverse temperature drops are determined.

Krasheninnikov, S.; Semenev, P.

doi: 10.1134/S0015462819050069pmid: N/A

Features of the processes of sound generation in turbulent jet flows are analyzed. Two possible processes are considered, namely, noise of dissipating turbulence and noise generated by largescale turbulent-flow perturbations which accompany propagation of turbulent jets. The data of the theoretical and experimental investigations of statistical turbulence theory are used to estimate the first of the above-mentioned effects. The data of computational experiments are used to analyze the process of sound generation by large-scale perturbations. In these numerical experiments time-dependent subsonic turbulent jet flows were directly calculated using the LES technology and the experimental data. It is shown that the noise of large-scale perturbations can be satisfactorily reproduced by the numerical simulation and its properties correspond to the experiments on studying sound generation in jets; the contribution of noise of dissipating turbulence to the total jet noise seems to be insignificant.

Sureshkumar, A.; Sridhar, B.

doi: 10.1134/S0015462819050082pmid: N/A

Experiments were conducted on overexpanded equilateral triangular supersonic jets (Mach 1.8) at Reynolds numbers 6.71 × 105 and 4.81 × 105 to study their decay and spread characteristics by means of measuring the jet centreline and lateral total pressure distributions. Schlieren images of the jets were also taken to study the shock patterns in the jet structure. The above Reynolds numbers correspond to the nozzle inlet total pressures of 550 kPa (6.71 × 105) and 360 kPa (4.81 × 105). For comparison purposes the above experiments were repeated on a circular nozzle with the same exit area and area ratio (1.44) and total pressures. The observations from the experiments reveal that the triangular jet exhibits a shorter supersonic core compared with the circular jet, i.e., reduction of 34.25% at 360 kPa and 31.11% at 550 kPa. The total pressure decay is more abrupt and a greater loss of the total pressure occurs closer to the nozzle exit plane in the case of the triangular jet compared to the circular jet. The lateral total pressure distribution reveals that the jet spreading rate is greater on the flat than on the corner side of the triangular jet.

Filatov, E.; Yakimov, A.

doi: 10.1134/S0015462819050033pmid: N/A

The results of experiments on the motion of a plate rigidly fastened to a dynamometric trolley performed in the water channel of Moscow State University are presented. The wave wake behind the body and the flow ahead of it in a finite-depth fluid were investigated at near-critical velocities of the motion and small planing angles. The observations show that a steady periodic wave wake occurs together with a nose wave of fixed shape, while in the case of detached rear waves the waves are excited ahead of the planing plate. The well-known Russell formula for the solitary wave amplitude is experimentally confirmed. It is shown that, accurate to small parameters, it coincides with Lavrent’ev’s results. The experimental conditions are numerically simulated using the XFlow™ software package. The results of the experiments performed in the water channel are in agreement with the numerical results.

Dudin, G.; Neiland, V.

doi: 10.1134/S0015462819040049pmid: N/A

The flow in the three-dimensional laminar boundary layer on a yawed flat plate of finite length is studied in the regime of strong viscous-inviscid interaction with a hypersonic flow. In the vicinity of the leading edge the flow functions are expanded in series under the assumption that the base pressure dependent on the transverse coordinate is given at the trailing edge of the plate. It is established that the expansions obtained include an indefinite function and its derivative with respect to the transverse coordinate. The corresponding boundary value problems are formulated and numerically solved, the eigenvalues are found, and it is shown that the exponent in the third term of the expansion differs from that in the second term only by one. The plate surface temperature effect on the flow parameters and the initiation of three-dimensional disturbances is investigated.

Grigor’ev, A.; Kolbneva, N.; Shiryaeva, S.

doi: 10.1134/S0015462819050045pmid: N/A

The analytical expression for the quadrupole moment of a charged conducting droplet caused by the presence of the self- and induced charges on the droplet surface is obtained. The droplet is assumed to be motionless in the superposition of gravitational and electrostatic fields. The analytical calculations are carried out in the first order in the dimensionless oscillation amplitude of the droplet. The intensity of electromagnetic radiation of the droplet generated by time variation in its quadrupole moment is estimated in the second order of smallness with respect to the square of the ratio of the characteristic linear droplet size to the length of emitted wave.

Afanasyev, A.

doi: 10.1134/S001546281905001Xpmid: N/A

The solution of the Buckley-Leverett problem classical for the theory of flow through a porous medium, generalized to the case of two-phase flows in fractured-porous media, is considered. In this case, immiscible displacement of fluid in the porous medium is complicated by the absence of local capillary equilibrium between pore spaces of different scales and in the generic case the solution of problem is not self-similar. The flow through a porous medium is considered in the limiting case of large time scales when capillary equilibrium is established and the flow parameter distributions, as shown in the study, tend to self-similar asymptotics. For the effective ordinary porous medium the average equations of equilibrium flow through the porous medium which describe these asymptotics are obtained

Tsypkin, G.

doi: 10.1134/S0015462819050094pmid: N/A

The problem of ice formation in unsaturated soil in the presence of pressure gradient and capillary forces is formulated. The complete system of conditions on the crystallization surface is derived. The one-dimensional problem is investigated in the self-similar formulation. The dependence of the amount of the ice formed on the problem parameters is also investigated. It is found that the ice saturation increases as the pressure on the cooling wall that initiates water inflow to the front decreases and also in the regime of more intense cooling. Increase in the pressure leads to water outflow from the front and decrease in the ice saturation.