Perturbed Arcs in Turbulent Axial Gas Flow II. Fluctuating Local Properties

As a continuation of the research described in Pt. I, local quantities are studied experimentally by electrostatic wall probing, time resolving shadowgraphy and radial luminosity profile scanning of arcs in turbulent axial gas flow. Turbulency of the gas coolant and thermal sheath properties are discussed as well as the consequencies of the gathered knowledge to theoretical modelling.     

Perturbed Arcs in Turbulent Axial Gas Flow. III. Numerical Simulation of Stochastically Disturbed Arc Discharges

Stochastically perturbed arcs are modelled by means of a Mayr type differential equation, the thermal constant τ being stochastically controlled by Gaussian fluctuations of given dispersion and correlation time: 1/τ = 1/τ₀ (1 + ζ). The ζ-signals are taken from an electronic noise source by an appropriately equipped intelligent CAMAC crate, which further processes the whole simulation program. Special cases treated are 1. stationary (in the mean) arc, 2. freely decaying arc, and additionally, 3. thermal reignition of a decaying arc with stiff recovery voltage.     

Experiments on Arc Perturbation in Turbulent Gas Flow

Electric arcs burning in a strong, turbulent, axial nitrogen gas flow are studied. Time-resolving (framing) picture series of the arc and its deformations are taken through the quartz tube channel wall. Individual perturbations like kinks exist under strong, turbulent flow conditions. They move with constant acceleration in the direction of the cold gas flow. The temperature of the arc core is disturbed at the position of these disturbances, too. This shows up most distinctly, if the decay of the arc after short-circuiting is studied, as has been done additionally.     

Radiative-Convective Heat Transfer in Discharge Chamber at Turbulent Gas Flow

In the paper radiative-convective heat transfer in electric arc flowed through by Ar in the discharge chamber is studied. The equation system for heat, mass and momentum transfer in boundary layer approximation is considered, and the turbulence model with radiation pulsation and electrodynamic values is suggested. By solution of the equation system with the help of finite differences method distributions of temperature, heat flows and turbulent transfer coefficients over chamber length were obtained. The radiation and turbulence influence on the electric arc characteristics is analysed.     

A Model of Heat and Mass Transfer in Gas Phase in Axial and Turbulent Dispersed Annular Flows

The problem of simulation of heat and mass transfer in the gas phase of film devices in the regime of weak and strong phase interaction has been solved. The Deissler three-layer model of turbulent boundary layer was used. Expressions have been derived for calculating the average Nusselt and Sherwood numbers. Examples of calculations for various conditions of phase interaction and comparison with experimental data are shown.     

Turbulent Heating Experiments in a Plasma Betatron

The various experiments carried out with the University of Saskatchewan plasma betatron are reviewed. The apparatus, having a major/minor radius of 19 cm/3 cm, a toroidal magnetic field B? ? 0.4 T and a heating field E? ? 12 kV/m, has been operated in different modes ? designated as betatron, tokamak and reversed - B?. The characteristics of the turbulently heated plasma and the physical processes occurring in each mode are discussed.     

Research on Thermal Effect of Window of High Power Fast Axial Flow CO2 Laser

Because of the thermal effect of window of high power fast axial flow (CO2 laser, the coupler will be distorted and become a convex lens. In this paper, the thermal distorted coupler is taken as a quasi-lens ABCD system, and through experiment and theoretical analysis, relations between the position of the output beam waist, the beam waist size, divergence angle, and the output power are given.     

Experiments to Explore the Mechanisms of Heat Transfer in Nanocrystalline Alumina/Water Nanofluid under Laminar and Turbulent Flow Conditions

Abstract

Heat transfer characteristics of water-based nanocrystalline alumina (Al₂O₃) nanofluids flowing through a uniformly heated tube under a fully developed laminar and turbulent flow regime is investigated experimentally in the present work to explore the heat transfer mechanism in nanofluids. In a laminar flow, the increase in Nusselt number was attributed to the thermophysical properties of the nanofluid. The movement of nanoparticles, along with the turbulent eddies in the turbulent core region and diffusion mechanism, such as thermophoresis, in the laminar sublayer are believed to be the reasons for enhanced heat transfer in turbulent region. The compatibility of Al₂O₃/water nanofluids was also examined by monitoring its color.     

Research on Thermal Effect of Window of High Power Fast Axial Flow CO_2 Laser

1 IntroduCtionIn the laser process of materials, when the cutout laser pew6r of a fast acal flowop laser is low and the coupler is flat in each Plane, the 'Waist of the output laser islocated on. the windoW. But when the output power increase, some phenomena willemerge and the output laser beam iS self-focussed. The main reason is that When theoutput power of the laser is high, the coupler thermal lens effect afl be resulted.adn the Phenomenon of coupler thermal lens effect of high power fa…     

基于真实气体效应的湍流标度律特性

在量热完全气体、热完全气体和化学反应完全气体等3种气体模型假设下,利用Mach数为4.05、壁温为1 300 K的超声速槽道湍流的直接数值模拟（direct numerical simulation,DNS）结果,对标度律和自相似性做了详细分析.结果表明,不仅在量热完全气体模型下存在标度律和扩展自相似性,而且在热完全气体和化学反应完全气体模型下标度律和扩展自相似性仍然成立.压缩性的影响使得速度结构函数通过Favre平均获得更为合适.与热完全气体模型的结果相比,化学反应完全气体和量热完全气体模型的结果吻合更好.      

三种湍流模式数值模拟直角弯管内三维分离流动的比较

采用有限体积法数值离散雷诺时均Navier Stokes方程,模拟了方形截面90°大曲率弯曲管道内的三维湍流流动.用3种湍流模式(标准k-ε湍流模式、RNG k-ε湍流模式、Realizable k-ε湍流模式)求解该问题.给出了数学模型和计算结果,并与实验数据进行了比较.结果表明,采用RNG k-ε湍流模式并结合两层壁面模型的处理,能有效准确地求解强曲率影响的管道内及近壁区湍流的流动.     

Synchronization in Turbulent Spherical Couette Flow Subject to Nonuniform Rotation

Technical Physics - The paper presents the results of numerical study of turbulent flows of viscous incompressible fluid in a rotating spherical layer in the presence of synchronization. The...     

高超声速可压缩流中粗糙壁热流研究

用计算流体力学（CFD）数值模拟和理论方法对高超声速可压缩湍流中粗糙壁面热增量进行研究. 着重考虑粗糙单元密度和粗糙单元形状对粗糙表面热流的影响. 结果表明： ①粗糙单元密度变化时, CFD数值方法计算所得的粗糙单元等效热流随着粗糙单元密度的降低而增加, 理论方法预测结果的规律随方法不同而不同;②在相同粗糙单元密度和高度时,如果粗糙单元形状改变,CFD计算结果也随之发生改变. 理论预测方法所得结果不发生变化.     

蒸汽浸没射流引起的紊流区轴向温度分布研究

本文采用紊态扩散模型分析了蒸汽浸没射流凝结过程,通过假设紊流区为单相水轴对称流动,利用自由紊动射流理论得到了紊流区轴向温度的计算公式。根据先前给出的温度特性半宽的实验关联式,得到蒸汽浸没射流引起的紊流区单相水射流的虚源,从而给出了计算紊流区轴向温度的半经验公式。本文中利用无量纲穿透长度确定了紊流区的起点位置,在此紊流区范围内,轴向温度的计算值和实验值吻合得较好,相对误差基本在±5%以内。     

Long Cycles in a Perturbed Mean Field Model of a Boson Gas

In this paper we give a precise mathematical formulation of the relation between Bose condensation and long cycles and prove its validity for the perturbed mean field model of a Bose gas. We decompose the total density ρ=ρ_short+ρ_long into the number density of particles belonging to cycles of finite length (ρ_short) and to infinitely long cycles (ρ_long) in the thermodynamic limit. For this model we prove that when there is Bose condensation, ρ_long is different from zero and identical to the condensate density. This is achieved through an application of the theory of large deviations. We discuss the possible equivalence of ρ_long≠ 0 with off-diagonal long range order and winding paths that occur in the path integral representation of the Bose gas