Fluid Dynamics最新文献

The results of energy analysis of the fragmentation regimes (puffing and microexplosion) of two-liquid droplets of the core-shell type are given. It is shown that using the classical energy approach to describe the hydrodynamic processes, it is possible to predict the critical (necessary and sufficient) conditions for the implementation of fragmentation regimes and their consequences. As distinct from the force approach, it is possible to estimate the discrete energies spent on evaporation, heating, fragmentation, viscous dissipation, and resistance during the motion of the fragmentation front.

An exact self-similar solution of the type of a traveling heat wave for the time-dependent nonlinear system of radiative-conductive heat transport equations in the Cartesian geometry is considered. The radiation component is considered in the kinetic model with specially adjusted absorption and scattering coefficients. An example of the test problem in the plane geometry is given.

Vapor flow in a gap between a liquid droplet and a hot wall caused by evaporation of liquid is considered. It is assumed that the wall temperature is higher than the minimum film boiling temperature, and there is no direct contact with liquid. In particular, the problem of such a flow arises in modeling post-dryout heat transfer, when droplets from a vapor–liquid flow fall onto the heated surface and partially evaporate on it, making a significant contribution to heat transfer. Within the framework of the problem under consideration, the gap between the droplet and the wall is assumed to be plane, and the vapor flow to be laminar and axisymmetric. An exact solution to the corresponding hydrodynamic problem is given.

The distinctive features of pressure wave dynamics in the presence of a porous partition (layer) saturated with a bubbly fluid are considered. It is shown that, depending on the parameters of the gas mixture and the porous medium (volume gas content, bubble dispersion, and porosity), reflection of a wave pulse from the porous partition saturated with a bubbly mixture is similar to reflection from the free boundary or from the rigid wall.

The results of the visualization of the matter transfer processes in colored free-fall drops, which mix with a transparent target fluid are analyzed. The parametrization is carried out basing on the system of fundamental equations of fluid mechanics which includes the equations of state for the density and the Gibbs potential. The contribution of different mechanisms of energy transfer is discussed; these are the macroscopic (including flows, waves, and vortices) and microscopic (dissipative and conversional) ones. The radiation transfer effect is not considered. The technique of the present-day experiments is descried, which allows to record accompanying acoustic signals together with the highly-resolving videorecording of colored flow pictures. The flow structure, dynamics, and energetics are analyzed for different density ratios of the confluent fluids and the kinetic and potential surface energies (PSE) of the drop. The conditions of the establishment of certain selected regimes, such as intrusive drop inflow, impact breakdown in fibers, and an intermediate hovering and rebound regime, are determined. A drop flowing smoothly into the fluid thickness at a small contact velocity in the intrusive regime forms a connected body. Thin trickles containing the matter of both media are formed in the contact spot in the impact mode. The fibrous wakes of the trickles form lineate and reticular structures on the fluid surface and within its thickness. In the intermediate regime the drop can hover on the fluid surface, touch it, merge partially with it, and rebound with the loss of the matter. The evolution of gas cavities and bubbles radiating acoustic packets is traced. The necessity of taking account for all the mechanisms of total energy transfer in describing hydrodynamics and acoustics of drop flows is noted.

The influence of transient heat and mass transfer processes in the melt, crystal and crucible on melt–solid interface shape and solute segregation in Bridgman growth of CdZnTe is investigated numerically. The computations elucidate a crucial role that the radial temperature gradient, formed by an interaction of latent heat release and external heat flux near the interface, plays in the evolution of the interface shape. Analysis of melt motion shows that solutal buoyancy force reduces the intensity of thermally induced convection up to a very low level. As a result, solute distribution in the melt is characteristic of diffusive transport regime. At the advanced stages of the process, when the growth interface moves slowly, and concentration of ZnTe in the melt becomes nearly homogeneous, complete mixing model is suitable for the description of axial ZnTe distribution in the crystal.

A theoretical model of a metering pump based on magnetic fluid containing a body of magnetizable material controlled by an applied variable uniform magnetic field is proposed. The model takes into account the nonlinear dependence of the magnetization of the magnetic fluid on the magnetic field. This makes it possible to consider the case of any (including strong) magnetic fields. Within the framework of this model, calculations of lifting a piston separating the magnetic and pumped fluids in various uniform magnetic fields are performed. The calculations based on the proposed model are compared with previous and new experiments. A good agreement between theory and experiment is obtained.

The results of studies of the jet formation process during the interaction of two colliding axisymmetric laminar air microjets. The axes of symmetry of the tubes lie in the same plane and intersect at an angle of 60°. The distance between the near ends of the tubes is equal to 4 mm. The outflow with identical velocities was implemented. As a result of the experiment, the distinctive features of the secondary jet formation under natural conditions and under the impact of an external periodic disturbance were revealed. It was found that the resulting jet is formed in the plane orthogonal to the tubes. Under natural conditions, a secondary jet with a beam angle greater than 115° is formed and represents a flattened jet. In the case of the external impact by a periodic acoustic signal, after the interaction of the microjets, a slight flattening appears with the development of secondary oscillations in the orthogonal plane and subsequent rotation with respect to the plane of the tubes.

The results of theoretical modeling of spherically symmetric expansion of collisionless carbon plasma from a compact explosive emission center of a vacuum discharge are presented. The modeling is based on the joint solution of the Vlasov kinetic equations for electrons and ions and the Poisson equation for the electric field, written in the spherical coordinate system and averaged over angular variables. It is shown that the calculated cathode plasma expansion velocities are significantly lower in the spherically symmetric geometry than the expansion velocities of plasma with the same parameters obtained by solving the plane problem. The observed expansion velocities of the cathode plume plasma at the level of 3.5 × 10⁶ cm/s can be explained within the framework of the collisionless mechanism when the criterion imposed on the ratio of the electric emission current to the limiting electric current in the vacuum gap is fulfilled.