Numerical Investigation of the Hydrodynamics of a Twisted Flow in a Vortex Chamber Based on the Two‐Parameter Model of Turbulence

An approach based on solution of complete averaged Navier–Stokes equations in vortex chambers using a lowReynolds k– model of turbulence is considered. The problem is solved in the variables vortex, stream function, and circular component of the velocity. The method of oriented pseudoconvection is used for problems of the dynamics of twisted flows. The method allows one to retain second order of accuracy of convective terms and provide stability of the solution for rather high Reynolds numbers. The problem of formulation of boundary conditions of second order of accuracy for vorticity on a solid wall at angular points is considered. An analysis of the results obtained shows that numerical calculations within the framework of the considered model of turbulence agree with experimental data rather well.     

Equalization of the Concentration of a Scalar Impurity in a Flow‐Type Chamber

Experimental and theoretical investigations of the time of equalization of the concentration of an impurity in a rectangular flowtype chamber have been carried out. It has been shown that the process of equalization of the concentration with time is exponential in character. The characteristic equalization time has been computed using the theory of turbulent diffusion. Theoretical results describe experimental regularities with an accuracy of about 10%. The value of the coefficient of turbulent diffusion for different configurations of flows in the chamber has been obtained from a comparison of experimental and calculated results.     

Numerical Calculation of the Flow Regimes of a Fluid Partially Filling a Horizontal Rotating Heat‐Exchange Cylinder

Consideration is given to a numerical determination of a twodimensional unsteady viscous flow with the free surface in a stationarily rotating horizontal cylinder in which heatexchange processes are carried out. The markerandcell method in a polar coordinate system is used. The features of modeling of the walllayer regime and the circulating flow regime that occur in rapid and slow rotation of the cylinder, respectively, are discussed. Based on the given results of numerical calculations, the influence of the Reynolds number on the character of flow is analyzed.     

Influence of Flow Angularities in a Hypersonic Ramjet Diffuser on the Formation of the Shock‐Wave Structure of the Real Gas Flow

We have investigated the shockwave structures arising at the entrance to the engine section of hypersonic aircraft and the influence on the process of their formation of the flow angularity after oblique shock fronts incident inside the diffuser with a different type of interaction (Mach or regular). To take into account the real properties of the atmosphere, we used the effective adiabatic exponent method permitting determination of the topology of shockwave patterns and calculation of the gas and thermodynamic parameters in various flow zones between the shock fronts in a wide range of diagnostic variables for the Earth's atmosphere.     

Numerical Modeling of Turbulent Flow inside a Wind‐Driven Plant with Allowance for the Forces on the Impeller

The operating efficiency of a winddriven plant based on a confuserdiffuser accelerator is evaluated within the framework of the multiblock approach to solution of steadystate Reynolds equations closed with the use of a twoparameter dissipative turbulence model.     

Change of the Sign of the Effect with Increase in the Intensity of High‐Frequency Acoustic Excitation of a Turbulent Jet

Results of an experimental investigation of highfrequency acoustic excitation of turbulent jets for different intensities of the acoustic field are presented. It is shown that upon reaching a certain limiting level of excitation at high frequencies, the sign of the effect changes, i.e., at this level, highfrequency excitation leads to generation of turbulence in the jet rather than its suppression. Hence it follows that the highfrequency acoustic effect that suppresses turbulence is most efficient within an optimum range of frequencies and at an optimum level of excitation.     

Analysis of the Thinning Mechanism of an Aluminum Alloy in Friction Stir Welding Based on the Indirect Extrusion–Vortex Flow Filling Model

Strength of Materials - Different morphology and thinning cases of the weld zone of a 7022 aluminum alloy in friction stir welding were analyzed. Metal plastic flow processes in the contact zone...     

Numerical Modeling of the Three‐Dimensional Unsteady Convection of a Silicon Melt in a Vessel Typical of Czochralski‐Method Apparatuses

Calculations of the quasiperiodic and stochastic regimes of threedimensional convection of a silicon melt (Pr = 0.015) have been performed for a rotating vessel whose complicated shape is typical of crucibles used in growing crystals by the Czochralski method. A large set of data on the structure of the convection and the spectral composition of pulsations has been obtained. The influence of the rotation of a crystal and a crucible on the convection and the thermal state of a melt has been investigated.     

Investigation of the Processes in Torches for High‐Speed Gas‐Plasma Spraying of Powder Materials with the Use of the Flow‐Rate Method of Action on the Flow

The comparative characteristic of torches with geometric and flowrate methods of control of the characteristics of a twophase flow are given. Based on the mathematical model proposed, the advantage of the flowrate method is shown by calculation. By using particular examples, the estimates of the optimum values are given for the relation of the flow rates in feeding units and for the length of the heating portion for torches with a flowrate method of control of the twophase flow.     

Application of the Electrochemical Method for Measuring the Fluid Velocity in a Two‐Phase Bubble Flow

A technique for measuring the fluid velocity in a twophase flow using a combination of the electrochemical method and the conduction method is described. The point of this technique is numerical analysis of complete realizations of signals from the electrodiffusion velocity transducer. The dependence of the results of measurements of local hydrodynamic characteristics of the bubble flow on the level of gasphase cutting out has been investigated. The measurement data for the local gas content, the fluid velocity, and the velocity pulsations during bubble mixture motion in a tilted channel are presented.     

Process of Cooling of a High‐Temperature Two‐Phase Flow

A technique and a design of a transducer for measuring the enthalpy of twophase flows using the thinwall method have been developed. Working formulas for calculating the heat capacity and the enthalpy of a gas flow are substantiated. Results of a test of the transducer in hightemperature flows of powder gases, including those after the packing of a coolant, are presented. The results obtained show that cooling of powder gases due to an endothermic reaction makes it possible to decrease the enthalpy flux by a factor of 5 and the temperature by a factor of 2.     

Heat Exchange on the Front Surface of a Blunt Body in a High‐Speed Flow Containing Low‐Inertia Particles

The method and results of an experimental investigation of the heat exchange on the front surface of a sphere in a supersonic flow containing particles of diameter d = 0.12–2.4 m and hollow particles of d = 160 m are presented. It has been revealed that in the case where even very small particles of d = 0.15 m are contained in an undisturbed flow and their concentration is low (of the order of a percent), the heat flux in the region of the critical point of the model markedly increases. A comparison of the experimental data with the data of calculations of the heat exchange in the region of the forward critical point which are based on the theory of a twophase laminar boundary layer has been made. A glow near the surface of the model was observed in the experiments conducted in total darkness.     

Analysis of Crystallization of a Supercooled Melt by the Integral‐Balance Method

Using the integralbalance method, the Stefan problem is solved for simply shaped crystals (a prism, a cylinder, and a sphere) grown in a supercooled melt. It is shown that the rate of crystal growth increases with the surfacetovolume ratio (in passage from a prism to a cylinder and a sphere). For all the three shapes of crystals studied the dependence of the speed of motion of the crystallization front on the supercooling is nonlinear and is characterized by a progressive increase.     

Enhancement of a Magnetic Field in a Perfectly Conducting Medium on Penetration of a High‐Velocity Jet into It

We consider the possibility of enhancement of a magnetic field created in a conducting medium on penetration into it of a highvelocity striker moving across the magneticinduction lines. For the case of a perfectly conducting target, an estimate is obtained for the rate of increase of the field intensity in the region of contact with the head part of the striker. A dimensionless parameter is introduced that characterizes the relationship between the rates of generation and diffusion of the field on penetration into a material of finite conductivity. Based on a model that takes into account the force action of a compressed field, the special features of the flow that arises on penetration of a highvelocity cumulative jet into a perfectly conducting target with a transverse magnetic field are analyzed.     

Identification of Heat‐Exchange Processes in a Supersonic Spatial Flow Past Aircraft

Direct and inverse problems of heat exchange in a supersonic spatial flow past the front part of an aircraft in the form of a spherically blunted nose cone have been solved numerically. The prospects of using highheatconductivity materials and the blowing of the gascoolant for lowering the temperature on the surface of an aerodynamic body have been shown. A comparison of the solutions of the direct and inverse problems in one, two, and threedimensional formulations for various materials of the sheath has been made. The error in recovering the heat flow by the thinwalled method has been estimated.     

Influence of Turbulence on the Deposition of Particles from a Gas‐Dispersed Flow on the Wall

Simulation of the scattering and deposition of dispersedphase particles in the region of interaction of a turbulent flow with an obstacle is considered. The regimes and distinctive features of deposition of particles in the vicinity of a critical point are investigated under different conditions. The sedimentation coefficient of the impurity is calculated as a function of the parameters of unperturbed flow and the particle size. The results of the calculations are compared to the data obtained without allowance for the influence of the fluctuations of the carrierflow velocity on the motion of the impurity.     

Gastrointestinal Transit Time:— An in Vitro Analysis of the Various Parameters Controlling the Critical Flow Velocity of Particles in a Horizontal Tube

Abstract

The factors which affect the critical flow velocity (V_c) of particles of barium sulphate, bismuth subcarbonate, kaolin, sulphadiazine and latex particles has been determined in a horizontal tube. These factors were particle size, particle density, fluid viscosity and tube diameter. V_c was found to increase with increasing particle diameter, particle density and tube diameter but decreases as viscosity of the flowing fluid. The results obtained were found to fit the models of Wicks, Durand and Wasp for the flow conditions of settled beds.     

Convective Heat Transfer in a Bubble Laminar Flow in a Round‐Cylinder Tube

The problem of heat exchange between a twophase laminar flow in a roundcylinder tube and the isothermal wall of the tube is studied. An exact analytical solution is obtained.     

Numerical Analysis of the Influence of Natural Convection on the Process of Condensation of Atmospheric Pollutant Compounds on the Surface of Near‐Ground Plants

Numerical investigations of the process of condensation of deleterious atmospheric impurities on the surface of nearground plants under the conditions of natural convective flows have been carried out. The influence of the latter near the surface of phytocenosis elements on the intensity of the process of condensation has been evaluated.