Free-stream turbulence levels are varied using grids across the test section, providing roughly a factor-of variation in the turbulence intensity. For low turbulence levels, the transition is dominated by stationary crossflow instabilities.
As the free-stream turbulence is increased, the traveling crossflow instabilities become increasingly relevant. For higher-turbulence and lower-roughness levels the transition appears to be dominated by the traveling crossflow instabilities. The results are linked to a variable N-factor method, which is shown to provide a good basis for estimating the transition location for low turbulence levels. The mathematical model of human respiratory tract has been constructed including four generations of bronchi.
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The volume-difference grid with 16? A numerical solution of the problem of flow in respiratory tract is obtained by the software package FLUENT on the base of Navier - Stokes equations with using turbulence model for low Reynolds numbers. The calculations of the flow in inspiration and expiration regimes are performed from nostrils to the fourth generation exit for quiet breathing conditions.
For both regimes the flow patterns are obtained which are far from symmetry due to anatomical features of nasal cavity, nasopharynx, pharynx and larynx. For conditions of the steady stationary flow the calculations are carried out for moving of inhaled submicron particles. These calculations used the Lagrange approach. Abstract  The problem of asymmetric incompressible axial flow in a corner formed of two intersecting plates at a right angle is considered.
The asymptotic behaviour of the flow far away from the corner is analysed. Two types of asymptotic behaviour are found. It is shown that the flow is very sensitive to the asymmetry parameter. A comparison of the results with computations of full Navier—Stokes equations was performed. Abstract  Calculation technology for modelling of two-dimensional detonation flows in a system of the reacting gas mixture-inert particles has been developed.
The problems associated with the cellular detonation suppression are researched. The interaction of the detonation wave with inert particles is modeled using the macro and micro approaches. Values of the volume concentration resulting in a change of the detonation cell size, weakening of the detonation wave, and suppression detonation are obtained. Secondly, a simulation of the detonation wave interaction with particles at the micro level has been carried out. A wave structure of the flow near the particles is obtained and the mechanism of detonation suppression was shown at volume concentrations of particles close to those obtained in modeling at the macro level.
Abstract  A mathematical model of two-phase medium using molecular-kinetic approach of theory of granular materials for the description of shock wave processes in gas particle suspensions with regard for particle-to-particle collisions is presented. The effect of collisional particle dynamics is analyzed in shock-wave and detonation processes.
The calculations of detonation flow in reactive particle suspensions in gas with presence of inert particles reveal that particle-to-particle collisions do not affect the detonation velocity, cell size and the flow structure behind the front but lead to dispersion the inert phase layer-type structures in the far zone of cellular detonation. The problems of a shock wave passage over a dense layer and the interaction of an explosive shock wave with a layer of particles are considered.
It is confirmed weak influence of the Saffman force and significant effect of the Magnus force on particle lifting from the layer directly behind the shock wave. It is shown that the development of chaotic motion and collisions is also one of the important mechanisms leading to the development of the dispersion of particles and formation of the dust clouds in the shock-wave processes. Abstract  In the paper the problem of heterogeneous detonation propagation in a circular tube and its exit into an open half-space is investigated on the model of monodisperse and bidisperse suspensions of aluminum particles in oxygen.
The regimes of propagation correspond to the classification established previously for flat channels. It is shown that geometric criteria of detonation propagation at the exit from the flat channels slots and circular tubes differ For bidisperse suspensions addition of fine particles has less influence on the transition from detonation failure to detonation propagation for circular tube than for a flat channel, which is apparently due to the greater contribution of the geometrical factor.
Abstract  The influence of a periodic supply of power pulses to the gas flow in a variable-section channel on the formation of shock structures in this flow was investigated. Parameters of the power supply providing different regimes of flow in the indicated channel and criteria of these regimes were determined on the basis of the solution of the problem of a powerful explosion with the use of the similarity theory and the homochronicity number.
The results of the numerical simulation of the flow in the variable-section channel with power supply in the quasi-one-dimensional approximation and of the flows in cylindrical and plane channels were compared.
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The applicability of the analytical dependences obtained was substantiated by the results of the numerical solution of the quasi-one-dimensional and two-dimensional Euler equations for the flow of an ideal gas in the indicated channels. Abstract  The structural features of self-fluxing coatings obtained by air-plasma spraying with a unit of annular injection of powder are discussed in the article. It is shown that the application of an annular injection unit makes it possible to increase significantly the efficiency of particle heating in contrast to the point injection of a powder into the plasma jet.
It is shown by optical and scanning electron microscopy that the major part of particles which form the coating is in a molten or plasticized condition in the plasma jet. To provide high technological and tribological properties it is necessary to carry out plasma spraying at an arc current less than Abstract  A model of nonequilibrium gas dynamics is proposed to describe ignition and combustion of a mixture of silane, hydrogen, oxygen, and an inert gas nitrogen or argon. The model is based on detailed chemical kinetics of nonequilibrium chemical reactions.
The model adequately describes the behavior of experimental data on the ignition delay time for this mixture versus the temperature behind the reflected shock wave in accordance with three criteria of ignition.
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The detonation wave velocity and equilibrium parameters of the mixture pressure and temperature are calculated as functions of the fuel-oxidizer equivalence ratio. Abstract  Using the method of molecular dynamics, the process of the rotary field formation in a metal nanostructure during its stretching at a constant deformation velocity was calculated. The analysis of the distribution of angular momenta in the space was conducted.
Abstract  Nanopowder production is associated with a number of technological challenges. The most common of existing production methods involve chemicals which can be dangerous and environmentally harmful. At the heart of our process is a method of obtaining powders by the evaporation of the raw material on industrial electron accelerator with power up to kWt and energy 1. From fundamental view it can be related with the generation of high-temperature aerosol.
The method is universal for a wide range of simple materials, nanopowder is produced in one stage, the technology allows to control the key parameters of finished products and is environmentally friendly.
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Advantages of the technology result in the advantages of the final products: particles size which ranges from 15 to nm can be controlled; small range of particle sizes; since the technology does not involve chemicals, the purity of the product is determined only by the purity of raw materials; the possibility to modify the surface of the particles; the combination of these factors allows the simultaneous control of the four parameters to produce nanopowders that ideally suit to the needs of each application. The nanopowders were tested in various areas, including functional materials.
Understanding of this phenomenon is not complete yet. Authors brought the model of associated layer on the nanoparticles surface to explain the experimental date. The theoretical background to adapt the Batchelor low for nanofluids was made.
Turbulent Impinging Jets into Porous Materials (Record no. 11838)
Reasonable change in Batchelor equation form for the nanoparticle concentration increasing has been substantiated. Agglomeration process was combined with the theoretical model. Also it was shown that the existence of associated layer leads to nanoparticles agglomeration is inevitable at some concentration.
The dependence of the critical concentration from the particle size was obtained. It was shown the volume concentration depended on the particle size and agglomeration level. For larger particles K is almost equal for fluids observed. The total temperature was measured by means of 5 gas-flow hromel-alumel thermocouples with the sizes of junction of 0.
Two approaches were used to reconstruct real temperature values and inertial characteristics of the measurement apparatus. Method of two thermocouples is based on usage of the positions of temperature maximum depending on time. Deconvolution method uses the solution of convolution integral equation. Thermocouples calibration was done by measurements of temperature steps.
Deconvolution method allows obtaining distinctive feature in the form of temperature peak, which is typical for the temperature distribution in impulse wind tunnels.
Abstract  The RANS high close approach for the turbulent fluxes of momentum, heat and mass for simulating of the circulation structure and dispersion pollutant over the urban heat island in a stably stratified environment under nearly calm conditions is formulated. Such the RANS approach minimizes difficulties in the turbulent transport modeling in a stably stratified environment and reduces efforts needed for the numerical implementation of the numerical model. The simulation results demonstrates that the three-four equations RANS approach is able to predict the structure of turbulent circulation flow induced by the heat island that is in good agreement with the experimental data.
Downloading of the abstract is permitted for personal use only. Abstract  The author has obtained equations describing thermal conductivity of composite bodies spatially reinforced with a system of smooth tubes in which an incompressible liquid heat-transfer agent is pumped in a developed turbulent regime. The corresponding boundary-value heat-conduction problem was formulated and its qualitative analysis was made. Specific calculations were performed for steady-state temperature fields in cylindrical concrete shells spirally reinforced with steel tubes through which a heat-transfer agent air is pumped.
A study has been made of the influence of the reinforcement parameters and of the velocity and direction of the heat-transfer agent in the tubes and the dimensions of their cross sections on the temperature field. It has been established that variation of these characteristics enables one to substantially change the intensity of heat removal from the shells, opening up wide opportunities for efficient control of the heat transfer in them. Abstract  An approach to the modeling of the process of the formation of thermal coatings lamellar structure, including plasma coatings, at the spraying of cermet powders is proposed.
The results are presented, which concern the development of the computational algorithm and the program complex for modeling the process of laying the splats in the coating with regard to the topology of its surface, which varies dynamically at the spraying, as well as the formation of lamellar structure and porosity of the coating. All these explain why plasma-sprayed cermet coatings have a comparatively high porosity at the interfaces between individual splats and at the coating—substrate interface.
Theoretical analysis of splat formation from porous cermet particle upon its impingement onto substrate was carried out taking into consideration the key physical parameters KPPs of particle—substrate interaction: temperature, velocity and size of cermet particle, substrate temperature, volume concentration of ultrafine solid refractory inclusions uniformly distributed in a liquid metal binder. The method is based on combination of mechanoactivation and SHS which is carried out in the free mode of combustion and does not demand additional mechanical power-consuming costs of grinding of intermediate synthesized compact.
Results of characterization of coatings received by means of atmospheric plasma spraying of powders of TiC-NiCr with various volume content of carbide inclusions are presented. It is explained by that, even knowing surface temperature of spraying particles, it is impossible to control the level of their bulk melting, due to low thermal conductivity of material and various residence time in the flow, which is characterized by considerable gradients of velocity and temperature. Abstract  Based on new information obtained on free microjets, this book explains the latest phenomena in flame evolution in the presence of a transverse acoustic field with round and plane propane microjet combustion.
It gives an overview of recent experimental results on instability and dynamics of jets at low Reynolds numbers and provides the reader, step by step, with the milestones and recent advances in jet flow stability and combustion. Readers will also discover a clarification of the differences between top-hat and parabolic round and plane jet instability.
Chapters demonstrate features of the interaction between jet and crossflow, and how experimental data testify to similarities of the perturbed flow patterns of laminar and turbulent round jets. A similar response of the jets to external acoustic oscillations is shown, as well as the peculiarities of the effect of a transverse acoustic field on downstream evolution of round and plane macro- and microjets. Basic features of round and plane, macro and micro jets' evolution affected by initial conditions at the nozzle outlet and by environmental perturbations are highlighted.
Students of fluid mechanics will gain a solid foundation in hydrodynamic stability and combustion of subsonic jet flow and researchers will value the presentation of special aspects of instability and transition. The work treats both theoretical and practical facets, and it includes supplementary material such as PowerPoint multimedia notes based on results of laboratory scientific experiments. Introduction Pages Evolution and breakdown of a subsonic round jet Pages Instability of free and wall plane jets Pages Round jet instability affected by initial conditions Pages Origination and evolution of coherent structures in laminar and turbulent round jets Pages Plane jets affected by initial conditions and acoustic perturbations Pages Round jets in a cross shear flow Pages Subsonic round and plane macro- and microjet in a transverse acoustic field Pages Stability of subsonic macro- and microjets and combustion Pages Zvegintsev V.
Braguntsov E. Melnikov A. Aulchenko S.
Vnuchkov D. Zaikovskii V. Lysenko V. Kuznetsov E.
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