Effect of the size of particles or drops on the diffusion of an impurity in a turbulent jet

Under the assumption that the. velocity of the particles entering into a mole at the start of its life differs from zero, an analog of the Schmidt number is determined with the turbulent flow of a mixture of a gas and solid particles. In accordance with the formula obtained, in the limiting case, where the particle size tends toward zero, the Schmidt number for a mixture of a gas and solid particles tends toward the Schmidt number for the gas. A model is proposed for determining the initial velocity of the particles in a mole. The results of a calculation of this velocity and of the analog of the Schmidt number, made using the proposed model, are in satisfactory agreement, respectively, with the values of the initial velocity, obtained indirectly from experiment, and with the mean Schmidt number for particles of small and medium sizes.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 18–23, July–August, 1975.     

The influence of magnetic field on the physical explosion of a heavy gas cloud

Richtmyer–Meshkov (RM) instability arises during the eruption of heavy gas cloud. In this study, we numerically study the effects of magnetic fields on the RM instability induced by the ionised cylindrical and spherical heavy gas cloud eruption using corner transport upwind + constrained transport algorithm. Our numerical results show that magnetic fields can suppress the formation of spike and bubble structures induced by the eruption in both cylindrical and spherical cases. The magnetic pressure of the interface along the perpendicular direction of magnetic field is the main factor to control the distortion of the interface. Even weak magnetic fields can drastically alter the evolution of the cloud and result in different distributions and amplifications of the magnetic pressure, which will affect further transformation of RM instability during the ionised gas eruption. Meanwhile, the magnetic pressure on the interface decreases gradually when the initial magnetic field is relatively large; when the initial magnetic field is small enough, the opposite results will occur.     

Numerical investigation of inviscid shock wave dynamics in an expansion tube

Highly complicated shock wave dynamics has been numerically calculated by solving the Euler equations for a circular shock tube suddenly expanded three times of the original tube diameter atx=0. Shock waves of different shock Mach number,M _s =1.5 and 2.0, have produced remarkably distinct blast jet structures. A planar shock wave took its final form after the blast by repeated Mach reflections of the blast wave: the first one at the wall and the second one at the central axis. The central Mach disc overtook and merged with the annular Mach stem before the planar shock wave was formed. In contrast to the blast wave which would propagate spherically in an open space, the present blast wave undergoes complex morphological transformation in the restricted flow passage, resulting in an unstable and oscillatory blast jet structure of highly rotational nature. The slipstream tube emanating from the shock tube exit corner decomposed into a chain of small vortex rings that interacted with the barrel shock of the jet, which caused periodic collapse of the jet structure. The finite volume-FCT formulation equipped with the time-dependenth-refinement adaptive unstructured triangular mesh technique in the present paper has contributed to resolution of the intricate physical discontinuities developing in the blast flow fields.     

爆炸容器内冲击波系演化及壳体响应的数值研究

对中心装药爆炸后冲击波的产生、传播和壳体动态响应全过程进行了数值研究。认为RDX瞬时爆炸 ,爆炸近场采用自相似解 ;冲击波传播和波系演化采用PPM (the Piecewise Parabolic Method)格式求解Eu ler方程 ;壳体响应采用有限元方法求解拉氏坐标系下由虚功原理得到的动力学方程。壳体内壁面边界条件分别采用强耦合和弱耦合方法处理。结果表明 :(1)当装药量相同时 ,薄壁壳体振型比厚壁壳体复杂得多 ,振幅也大 ;(2 )当装药量不同 ,壳体厚度相同时 ,爆炸场冲击波的演化过程不同 ;(3)对少量装药 ,产生的冲击波强度低 ,壳体变形小 ,是否考虑内边界运动 ,对计算结果的影响不大 ;(4 )在本文条件下 ,爆炸容器封头顶点所受的载荷最大 ,是最易发生破坏的地方 ,侧壁与爆点所在横截面的交线 ,也易破坏。     

Interaction forces of particles dispersed in an electrolyte

Expressions are derived for the forces acting in a disperse medium in the presence of interaction of the double layers surrounding particles or drops of the dispersed phase when the potential of the dispersed particles is small. It is found that the force produced by the presence of double layers is proportional to the concentration gradient of the dispersed particles. It is shown that this force is comparable with the force produced by Brownian motion of the particles and may even exceed it. The equations of motion for the dispersed phase are derived with allowance for the convective terms, the pressure gradient, and the forces caused by Brownian motion and the presence of the double layers. A generalized Fick's law is obtained with effective diffusion coefficient. The equilibrium distribution of the particle concentration in a uniformly rotating cylinder is found with allowance for the interaction of the double layers.Translated from Izvestiya Akademii Nauk SSSR, Meklianika Zhidkosti i Gaza, No. 5, pp. 98–102, September–October, 1984.     

Experimental investigation of the motion of cylindrical shells under the action of the products of an explosion in a cavity

An investigation was made of the motion of a cylindrical shell under the action of the products of an explosion in a cavity. An incompressible, nonviscous shell without strength was considered. The method of pulsed x-ray photography, with recording by the shadow method in a streak camera, was used to investigate the motion of shells made of alloy D16, brass, copper, and lead, with different degrees of filling of the cavity of the shells by the charge of explosive. The experimental and calculated results are compared. The agreement between the experimental results and calculation is satisfactory.     

Evaporation and explosion of liquid drops on a heated surface

The literature pertinent to various aspects of drop evaporation on a heated surface is reviewed. Both the laser shadowgraphic and direct photographic methods are employed to study thermal stability and flow structures in evaporating drops in all heating regimes. It is revealed that four flow regions exist in stable and unstable type drops at low liquid-film type vaporization regime. As the surface temperature is raised, the flow regions reduce to two. In the nucleate-boiling type vaporization regime, the interfacial flow structure changes due to a reduction in the Marangoni number as well as the dielectric constant of the liquid. An evidence of bubble growth in the drops is disclosed. The micro explosion of drops is found to occur in the transition-boiling type heating range. No drop explosion takes place in the spheriodal vaporization regime except when the drop rolls on to a microscratch on the heating surface. It is concluded that the mechanisms for triggering drop explosion include the spontaneous nucleation and growth phenomena and the destabilization of film boiling.     

Trajectories of charged solid particles in an air jet under the influence of an electrostatic field

Among modern coating techniques electrostatic powder spraying is one of the most attractive. In this method the plastic particles are charged by a high voltage electrode inside a coating gun. The charged particles are entrained by an air jet and directed towards the object to be coated, which is electrically grounded.In the present paper experimental trajectories of particles emerging from an electrostatic gun are determined. The equations of motion of particles in a jet are written in Lagrangean coordinates and solved numerically. Results are compared with the experimental data.     

Numerical modeling of an underwater explosion in an air cavity

An efficient numerical algorithm based on Godunov method is proposed that permits qualitative and quantitative calculations of the hydrodynamic flows resulting from the detonation of explosive charges in an air cavity. Calculations are performed by a difference scheme using moving difference grids in which the moving boundaries are the contact surfaces between the detonation products and air and between air and water, and the shock-wave front. The reliability of the calculations is confirmed by experimental data. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev 252057. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 4, pp. 33–37, July–August, 1998.     

Rotation of dispersed particles in a vortex field

An expression is obtained for the angular velocity of a spherical dispersed particle in a viscous fluid in an external vortex field with an harmonic time dependence. This expression is then used for investigating a system of two rotating dispersed particles whose rotation is the result of the interaction of the particles in the field of an incident sound wave. It is found that such a system possesses a rather interesting nontrivial property: under certain conditions it has a resonant frequency at which the rotation of the particles relative to the fluid is most intense.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 186–188, July–August, 1992.     

Dynamics and spatial boundaries of retardation of the plasma cloud of an explosion in a dipole magnetic field

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 6, pp. 3–10, November–December, 1993.     

Motion of a cloud of particles under gravity and its sedimentation on a flat horizontal surface

On the basis of the nonstationary two-dimensional equations of the mechanics of heterogeneous media a numerical investigation is made of the motion of a cloud of particles under the influence of gravity in an unbounded medium and the interaction of the descending cloud of particles with a flat horizontal surface. Depending on the degree of hydrodynamic interaction between the particles, there are different regimes of motion of the cloud during sedimentation; the change in its spatial configuration determined by the large-scale vortex motion of the carrier medium is determined. The concentration distributions of the particles on the sedimentation surface are obtained. A coefficient of dispersal is introduced for the cloud of particles on the flat horizontal surface, and its dependence on the concentration of the particles, their diameters, and other parameters is investigated.     

Lyapunov-stable equilibrium distribution of charged particles in an ionized-gas cloud

The solution of several problems requires establishing the equilibrium spatial distribution of the charged particles in an ionized-gas cloud having fixed shape and given dimensions.In the present study we find the Lyapunov-stable equilibrium spatial distribution of the charged particles in an ionized-gas cloud enclosed in a region of space with fixed form and given dimensions. An expression is obtained for the limiting energy stored by the ionized gas for given degree of ionization of neutral gas, and expressions are found for the pressure and chemical potential of the ionized gas in the cloud. We use the general method for the solution of a particular type of extremal problem presented in [1, 2], which reduces the optimization problem to the solution of the corresponding inverse problem of potential theory.In conclusion I would like to thank N. N. Bogolyubov, B. B. Kadomtsev, and Yu. N. Barabanenkov for their discussions of the present study and helpful comments.     

Experimental investigation of the atomization of drops of liquid under conditions of a gradual rise in the external forces

The article gives the results of an experiment on the effect of the physical properties of the liquid and the phase-contact time on atomization of drops under conditions of a gradual rise in the aerodynamic forces of the flow. It is shown that the value of the critical Weber number and the mechanism of the atomization of a drop are determined both by the conditions of the change in the relative velocity of the gas flow at the moment preceding atomization of the drop and by the values of the viscosity complex and the phase-contact time.     

Numerical investigation of unsteady subsonic viscous gas flows in a plane channel with a sudden expansion

The nonlinear processes of development of instability in an unsteady subsonic viscous gas flow in a plane channel with a sudden expansion are investigated numerically with allowance for acoustico-vortex interaction over a broad interval of the characteristic parameters. Effects associated with the acoustic self-excitation of the jet flowing into the wider part of the channel are determined. Approximate relations are obtained for the resonance conditions of self-excitation. The effect of the inlet mean-velocity profiles on the evolution of the flow is estimated. The processes of formation and subsequent interaction of the coherent structures are analyzed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 32–41, July–August, 1988.