倾斜射流对移动平板表面紊动和传热特性的影响

采用雷诺应力湍流模型和Simplic算法对半封闭槽道内倾斜射流冲击移动平板的流动和传热特性进行了数值模拟,研究了不同射流角度和不同平板移动速度下平板近壁湍动能和板面努塞尔数的变化.结果表明：射流角度和平板运动速度对平板近壁湍动能和表面努塞尔数值分布影响显著;当入射角与平板运动方向相同时,板速的升高提高了近壁面的湍动能,但是降低了冲击区域的局部努塞尔数值;平板表面的平均努塞尔数值随板速的提高先降低后大幅升高,高速下角度对平板表面的平均传热效果影响较小;当入射角为80°,平板运动方向与入射方向相反且板速和射流速度相同时,在移动平板表面能够获得较佳的紊动和传热效果.     

Large-Eddy Simulations and Heat-Flux Modeling in a Turbulent Impinging Jet

This article documents the results of an investigation into aspects of the simulation and modeling of turbulent jets that impinge orthogonally on a target surface. The focus is on the case of a jet which issues from a circular pipe into stagnant surrounding at the relatively high value of Reynolds number of 23,000 (based on nozzle diameter and bulk velocity) for which experimental data are available. Large-eddy simulations were performed to obtain details of the mean flows and the turbulence fields including distributions of all components of the turbulent heat fluxes. The outcome of these simulations were used to assess three alternative models for the turbulent heat fluxes which differ from the conventional Fourier's Law by not being based on the assumption of proportionality between the eddy and thermal diffusivities via a constant Prandtl number. It was found that only one of the models considered succeeds in representing the effects on the heat fluxes of the complex strain field associated with the stagnation region and the subsequent development into the wall-jet region. The reasons for this outcome are discussed.     

A Turbulent Impinging Jet on a Plate Covered with a Porous Layer

This work shows numerical results for a turbulent jet impinging against a flat plane covered with a layer of permeable material, which is kept at a higher temperature than that of the incoming fluid. Parameters such as porosity, permeability, thickness, and thermal conductivity of the porous layer are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure–velocity coupling. Results indicate that inclusion of a porous layer decreases the peak in Nu avoiding excessive heating or cooling at the stagnation point. Also found, was that the integral heat flux from the wall is enhanced for certain ranges of values of porosity, layer thickness, and thermal conductivity ratio.     

喷嘴结构对多孔喷油器喷射特性影响的研究

利用EFS8246单次喷射测量系统和高速闪光摄影系统对不同结构参数的非轴对称喷嘴的喷油规律和油束形态进行了试验研究.利用CFD软件Fire的两相流模型对各喷嘴内部流动和气蚀现象进行了仿真模拟.喷嘴结构参数包括喷孔数、喷孔直径、喷孔夹角和喷孔长径比.研究结果表明:各结构参数对喷嘴流量系数、雾束形态、各孔间流量差异、各次喷射的一致性均有不同程度的影响,而具体的影响程度由压力室和喷孔内的气穴强度决定.     

Free Liquid Jet Impingement from a Slot Nozzle to a Curved Plate

This article explores the heat transfer characteristics of a free liquid jet discharging from a slot nozzle and impinging vertically on a curved cylindrical shaped plate of finite thickness. Computations were done for Re = 500–1800, β = 0.75–3, R _i /d _n  = 4.16–16.66, b/d _n  = 0.08–1.5, and d _n  = 0.3–2.4 mm. Results are presented for dimensionless solid–fluid interface temperature, dimensionless maximum temperature in the solid, and local and average Nusselt numbers. The local Nusselt number increases with Reynolds number. Decreasing the nozzle width increases the local heat transfer coefficient. Decreasing the nozzle to target spacing or plate thickness or plate inner radius of curvature all enhances the Nusselt number.     

Heat Transfer and Thermal Characteristics Effects on Moving Plate Impinging from Cu-Water Nanofluid Jet

The present article is focused on modelling of flow and heat transfer behaviour of Cu-water nanofluid in a confined slot jet impingement on hot moving plate. Different parameters such as various moving plate velocities, nanoparticles at various concentrations, variation in turbulent Reynolds number and jet nozzle to plate distance have been considered to study the flow field and convective heat transfer performance of the system. Results of distribution of local and average Nusselt number and sk...     

Thermal Analysis of an Impinging Jet on a Plate With and Without a Porous Layer

This work shows numerical results for a jet impinging against a flat plane covered with a layer of a porous material, which is maintained at a higher temperature than the incoming fluid. Parameters such as permeability and thickness of the porous layer and thermal conductivity ration are varied in order to analyze their effects on the local distribution of Nu. The macroscopic equations for mass, momentum, and energy are obtained based on a volume-average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted nonorthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that inclusion of a porous layer decreases the peak in Nu avoiding excessive heating or cooling at the stagnation point. Also found was that the integral heat flux from the wall is enhanced for certain range of values of layer thickness, porosity, and thermal conductivity ratio.     

高热流密度量热探针的设计与实验

以热等离子体射流冲击平板传热的热流密度测量为背景,分析比较了文献中报道过的各种测量高热流密度的量热探针的结构及实验方法;结合特定实验条件,设计了新型量热探针并对其测量高热流密度的方法误差进行了分析,描述了实际测量采用的方法,给出若干初步实验结果。     

Experimental and Numerical Study on Heat Transfer with Impinging Circular Jet on a Convex Hemispherical Surface

In this paper, the experimental and numerical study has been carried out to investigate the water jet impingement on a convex hemispherical surface. The pressure and skin friction coefficient distributions on the impingement surface were analyzed numerically. A great deal of attention was paid to analyze the effects of the jet impingement exit velocity and the nozzle-to-surface distance on the heat transfer characteristics. A comparison of the heat transfer coefficient was performed between the jet impingement on the convex surface and the flat plate. The results show that the Nusselt number for the convex surface is higher than that for the flat surface. The local Nusselt number is decreased monotonically from its maximum value at the stagnation point for lower Reynolds numbers. A secondary maxima occurs for higher Reynolds numbers. The experiment and simulation were performed with the following parameters: the jet impingement Reynolds number of Re = 1947–19478, and the nozzle-to-surface distance of L/D = 2.5–25.     

Experimental Investigation on Thermal Protection of High Temperature and High Velocity Jet Impinging a Cross-Shaped plate

Abstract

This paper investigated the heat transfer of high temperature jet impinging a cross-shaped plate. An experimental mockup was designed and used to produce high temperature (～500?°C) impinging gas jet with stable high speed (～56?m/s) at the nozzle exit. A one-dimensional theoretical model was proposed to predict the temperature increment of the back-side surface(s) that opposed to the impinging surface, by simplifying and assuming the heat transfer process can be governed by convection. Three materials were selected due to its potential high heat transfer resistance, speedy installation and long duration under severe impinging conditions. For each material, four types of thermal insulation structures were designed and subjected for testing. The following conclusions from comparison of the results of the model predictions with experimental data can be drawn. The proposed simplified one-dimensional model can be used to predict heat transfer at the back-side under high temperature and high-speed impinging. The optimal case among the 12 thermal protecting designs was obtained, majorly due to low back temperature and less material consumption.     

非定常喷嘴射流形状预测研究

在对射流进行非定常CFD解析的基础上，提出了射流直径的计算公式和射流形状的统计预测方法，并由时间平均的射流形状确定了缩流位置、膨胀率等用于设计的重要参数。     

LES of a Turbulent Slot Impinging Jet to Predict Fluid Flow and Heat Transfer

In this article, large eddy simulation (LES) is performed for a turbulent slot jet impingement heat transfer at a Reynolds number of 13,500 and a nozzle to plate spacing of 10. Various aspects of predicting a turbulent jet impinging flow in an optimum domain size and grid resolution for LES have been assessed. Two inflow conditions, one without any fluctuations and the other with fluctuations generated by the spectral synthesizer, were tested and comparisons of various mean flow, turbulence, and heat transfer data showed that LES without any inflow fluctuations provides good agreement with the corresponding experimental and numerical results reported in the literature. Further, various important dynamical flow structures have been visualized from the instantaneous computed data. Finally, mean flow and turbulence statistics have been presented in the wall jet region close to the stagnation point, which could be useful as data for validation of RANS-based turbulence models.     

矩形管湍流冲击射流流动与传热的数值研究

采用SIMPLE算法和RNG k-ε湍流模型,通过求解三维N-S方程和能量方程,对雷诺数为10000和冲击高度为4倍喷管水力直径的矩形管湍流冲击射流进行了数值模拟。结果发现在冲击面附近的射流横截面上,伴随着两个反向旋转涡对的出现,形成了主流速度的两个偏心峰值。分析认为双偏心速度峰值的形成是由冲击面产生的涡量向上游截面扩散而引起的。温度场和冲击面局部№数分布的研究结果表明：射流的传热特性受流动结构的控制,采用矩形管湍流射流可以获得较大的冲击区和较均匀的冷却效果。     

喷流式退火炉炉内卷材尺寸对换热过程的影响

利用FLUENT软件对铝卷材喷流退火过程进行模拟计算,模型耦合求解炉内温度场及流场。讨论退火过程卷材规格不同对卷材截面换热的影响,得到卷重及宽度不同时料卷芯部与端部温升的变化规律。     

Investigation of a Confined Laminar Impinging Jet on a Plate with a Porous Layer Using the Preconditioned Density-Based Algorithm

The preconditioned density-based algorithm and two-domain approach were used to investigate the fluid flow and heat transfer characteristics of a confined laminar impinging jet on a plate covered with porous layer. In the porous zone, the momentum equations were formulated by the Darcy-Brinkman-Forchheimer model; the thermal nonequilibrium model was adopted for the energy equation. At the porous/fluid interface, the applicability and influence of different hydrodynamic and thermal interfacial conditions were analyzed for the problem. The governing equations were solved by the preconditioned density-based finite-volume method, with preconditioning matrix for equations of porous domain adopted, aiming to eliminate the equation stiffness of porous seepage flows. The effects of Reynolds number, porosity, Darcy number, thermal conductivity ratio, Biot number, and porous layer thickness on the flow pattern and local heat transfer performance were studied. Results indicate that the Reynolds number and porosity don't strongly influence the flow pattern of porous channel, while the Darcy number and porous layer thickness have obvious influence on the flow pattern. The heat transfer performance are greatly influenced by the parameters studied.     

高压甲烷气体碰壁射流扩散与卷吸特性的试验

在定容装置上利用高速摄影纹影法开展了不同冲击高度和冲击角度下的甲烷高压碰壁射流扩散和卷吸特性试验.通过纹影照片得到了不同冲击高度和冲击角度下的射流贯穿距离随时间变化的规律,计算得到了射流卷吸空气质量随时间变化的规律.结果表明:碰壁射流发展分两个阶段,碰壁之前贯穿距离和卷吸空气质量与自由射流基本相同;碰壁之后,由于壁面阻力的作用,其贯穿距离和卷吸空气质量的增加速率低于自由射流.随着冲击高度的增加,碰壁射流贯穿距离和卷吸空气质量增大;随着冲击角度的减小,碰壁射流贯穿距离和卷吸空气质量增大.最后对Poreh碰壁射流贯穿距离和卷吸空气质量经验公式进行修改,使其适用于一般碰壁射流贯穿距离和卷吸空气质量的特性计算.     

燃烧室壁面形状对撞壁射流气体混合过程的影响

本文研究了燃烧室壁面形状对撞壁射流气体沿壁发展过程的影响，实验发现：射流气体撞壁后主要沿壁面发展；近壁区域会形成浓混合气层，并且混合很慢，本文提出了两种方法，１）在壁面设置矩形凹槽，并且利用环境的气流运动加快射流气体的混合。２）在壁面上设置条形障碍物，使射流气体脱离壁面形成空间流动，另外，本文也模拟了ＯＳＫＡ－Ｄ燃烧系统中燃油撞壁后的发展过程。     

Numerical Study of Controlling Jet Flow and Noise using Pores on Nozzle Inner Wall

In this paper, the feasibility of controlling the subsonic jet flow and its noise using pores of blind holes added on the nozzle inner wall is explored numerically. These pores are intended to introduce disturbances to the shear layer so as to change the flow mixing. This passive strategy has not been attempted so far.A convergent nozzle with a cylindrical extension is selected as the baseline case. Three nozzles with pores on the inner wall are set up. Validations of the numerical settings are carried out, then the compressible turbulent jets at the exit Mach number M _j = 0.6 in the four nozzles are calculated by large eddy simulations (LES), while the radiated sounds are predicted by the FW-H acoustic analogy. The results show that the blind holes have produced some effects on weakening the turbulence intensity in the shear layer. Comparison reveals that both temporal and spatial correlations of the turbulent fluctuations in the modified cases are suppressed to some extent. Meanwhile, the porous nozzles are shown to suppress the pairing of vortices and enhance the flow mixing, and therefore, the development of shear layer and the fragmentation of large scale vortices are accelerated.     

Heat Transfer Characteristics outside the Condenser of a Rotating Heat Pipe Grinding Wheel with a Lateral Air Impinging Jet

This study numerically analyzed the heat transfer characteristics outside the condenser of a rotating heat pipe grinding wheel (RHP-GW).The goal of this investigation is to determine the optimal structure and parameters for the condenser section of RHP-GW.Different fin height (f=0–7 mm),rotational Reynolds number(Re_r=1602–6408) and jet Reynolds number (Re_j=42 379–108 302) were analyzed under input heat flux of 4000W/m~2.A fully developed flow was imposed at the outlet of the nozzles.Results showed that the optimal heat transfer rate was obtained for fin height of 5 mm,which improved the average Nusselt number by 84%compared to the structure without fins.A critical Re_j for each Re_r that the impinging jet can reach the condenser section was found.The critical Re_j value increases with Re_r,which is in the range from 42 379 to 61 215 and 61 215 to 80 050for Re_r=6408 and Re_r=9610,respectively.