Vol 51, No 2 (2016)

A fine structure of the flows developing during primary contact of freely falling drops with a deep quiescent fluid is studied using the macrophotography and high-speed video filming methods. Water drops falling in water, alcohol, and oil, as well as drops of oil, petroleum, and aqueous solutions of salt or alcohol falling in water are investigated. The work is focused on the visualization of the finespray scattering from the primary contact area. The collisions of small droplets with the surface of the submerging drop are first recorded. The direction of the spray and streamer scattering is determined by the surface tension coefficients of the coalescing liquids. The conditions under which the spray droplets collide with the drop surface are determined.

An exact time-dependent solution of the system of Navier–Stokes equations governing large-scale viscous vortical incompressible flows is derived. The solution generalizes that describing the Couette flow. Two ways of preassigning the boundary conditions at the upper boundary of a fluid layer are considered. These are the time-dependent variation of the velocity value with the conservation of its direction and the variation of the angle at which the velocities parallel to the coordinate axes are directed. It is shown that at certain values of vorticity, viscosity, and the layer thickness the velocities within the layer can be severalfold greater than the given velocity at the boundary.

The manifestations of the cyclone-anticyclone asymmetry on the stability of rotating shear flows are investigated both theoretically and experimentally. The stability of certain classes of shear flows, namely, rotating tangential discontinuities and flows with a constant shear, is analyzed. The dependence of the disturbance growth rate on the sign and absolute value of the shear is determined. The three-dimensional disturbances leading to longitudinal flow modulations are shown to be most dangerous. The results of the observations of the cyclone-anticyclone asymmetry effect in the laboratory conditions are presented.

Turbulent flow of nanofluids based on the distilled water with aluminum and silicon oxide particles of different sizes in a cylindrical channel is studied. The results of the measurements of the heat transfer coefficient and the pressure difference are presented. The maximum volume concentration of the particles was not greater than two percents. The dependence of the heat transfer coefficient on the nanoparticle concentration and their sizes and material is studied. It is shown that a considerable increase in the nanofluid heat transfer coefficient, compared with the corresponding value for water, may generally be expected. At the same time, the heat transfer coefficient of a nanofluid depends on the nanoparticle size and material; because of this, under certain conditions the nanofluid heat transfer coefficient can turn out to be lower than that of the baseline fluid. Situations, when this can occur, are established. It is for the first time experimentally shown that the nanofluid viscosity coefficient depends not only on the nanoparticle size but also on its material.

An analytical solution of the problem of the wave action of a double-layer finite-depth circulatory flow on a dipole is derived. The cases in which the dipole is located in the upper and in the lower layer are considered. The values of the flow parameters at which the wave drag and the lift of the dipole become maximum are determined. The examples of numerical calculations under actual sea conditions, that is, in the presence of density jumps and with account for the sea depth, are presented. The singular cases of the lift variation are established.

Capillary imbibition of a wetting fluid in a porous medium is studied. A method of constructing the exact solution of the corresponding problem is developed. An iteration procedure is developed for the case of countercurrent capillary imbibition. The salient features of the flow generated by capillary forces are revealed on the basis of numerical results.

The results of experimental studies and theoretical analysis of the dynamics of a spherical bubble rising in a liquid with surfactants are presented for a wide range of Reynolds numbers. A refined empirical dependence for the bubble drag coefficient in the steady-state regime at Re < 1 is obtained. The influence of surfactants on the bubble shape and rising velocity in the transient regime is analyzed.

The results of a numerical and experimental investigation of the starting of jet-engine annular nozzle blown with the air at room temperature and high-temperature combustion products of a stoichiometric acetylene-air mixture in an intermittent aerodynamic setup are presented. The regimes and the times of the attainment of quasi-steady stAte of the flow are studied in the virtual full-scale counterpart of the experimental setup. The special features of the starting stage and the quasi-steady flow are studied for entry channels of different shapes. The values of starting times, the pressures at different points of the flow duct, and the thrusts produced by the annular nozzle measured in the physical experiment and obtained in the virtual experimental setup are compared.