An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.     

微细磨料喷射加工仿真与实验研究

利用流体动力学仿真软件CFX对微细磨料喷射加工中,影响加工效果的喷射压力、喷射距离等影响因素进行仿真,模拟出不同参数下磨料微粒的速度、工件表面所受压力的分布规律,并与实验结果进行对比,验证仿真结果的正确性.     

磨料水射流钻削深小盲孔的试验研究

论述用连续磨料水射流钻削深小孔的试验研究.磨料水射流的加工领域非常广泛,它可以在许多材料上进行加工,加工的主要优点是加工时不产生切削热,加工过程非常灵活.所采用的钻削加工是在不同材料上进行的,随着钻削时间的不同,可观察到钻孔的深度和直径都不同.孔的深度和直径与钻削时间呈幂甬数关系增大.根据试验结果可以创建一个经验模型,预测在不同钻削时间,钻孔的深度和直径的大小.     

磨料水射流仿真分析与试验研究

为有效保持油田的稳产增产,磨料水射流技术逐渐被应用于油田生产.磨料水射流切割利用高速混砂液体的射流来完成切割作业,具有安全、多能、环保、便捷、高效的特点.本文对前混式磨料水射流切割的喷嘴结构进行了优化设计计算,采用计算流体力学的方法,利用CFD仿真软件,对不同喷嘴类型﹑喷嘴长度和不同锥角角度的喷头的工作情况进行数值模拟...     

Numerical simulation for abrasive water jet machining based on ALE algorithm

In dealing with fluid impact and large deformation problems by traditional Lagrange grid, calculation failure often happens due to grid distortion. An abrasive water jet machining model is created to simulate the whole stage by software LS-DYNA from the jet into the nozzle to the workpiece material removal process using ALE (Arbitrary Lagrange–Euler) algorithm. The mesh for the abrasive and water is based on the ALE formulation, while the target mesh applies the Lagrange formulation. The effect of jet penetration is implemented by coupling the grids of ALE and Lagrange. The jet traverse speed is achieved by definition of the movement of ALE grid to reduce the mesh domain. The abrasive constitutive equations are also presented in this paper. The uniform mixture for abrasive and water is achieved by definition of volume percentage of the two materials in the initial ALE elements. Simulation results give the relationships between processing parameters and the cutting depth. The good agreement between simulation results and experimental data verifies the correctness of the simulation.     

淹没磨料水射流与非淹没磨料水射流冲蚀破岩效果比对分析

磨料水射流的冲蚀能力主要依赖于磨料颗粒所获得的能量,对非淹没磨料水射流和淹没磨料水射流的冲蚀实验结果进行比对,从能量角度和磨料颗粒速度变化角度分析了造成非淹没磨料水射流和淹没磨料水射流的冲蚀效果差异的原因。     

Numerical study on the effects of a synthetic jet actuator on S809 airfoil aerodynamics at different flow regimes and jet flow angles

Due to importance of active flow control methods for future Horizontal axis wind turbines (HAWT), we numerically investigated the effects of Synthetic jet actuators (SJA) on the separation and aerodynamic lift enhancement of a finite span wing with the S809 airfoil. The investigation was performed at a realistic AOA range (0°~25°), which is associated to a wide range of AOA, from an attached flow to a highly separated condition. Also, effects of SJA injection angle on flow characteristics at a highly separated condition were studied. The unsteady simulations were performed using DES turbulence model. The results show that for an attached flow, the SJA triggers an early separation and reduces the lift coefficients. However, for a separated flow, the SJA considerably enhances lift performance. In addition, at small AOAs the lift values fluctuate harmonically over time; however, as the AOA increases and the separation becomes severe, the lift becomes more chaotic. Finally, a study of the present SJA configuration reveals that the SJA can enhance the lift values at a wide range of injected flow angle. However, lift values do not show distinguished pattern for different jet angles at a high AOA.

     

Numerical and experimental study on the thermal characteristics of a steam reformer

In this study, the performance evaluation of a cylindrical natural-gas steam reformer is experimentally and numerically performed with a special focus on thermal operation conditions. The evaluation system is configured to probe the thermal and chemical characteristics of a steam reformer that does not employ a high temperature shift and a low temperature shift. The acquired experimental data is used to validate the proposed numerical model. A combination of experimental and numerical data provides detailed information leading to a better understanding of the internal reaction. An appropriate control of the heat source in the steam reformer is extremely important because the endothermic process is dominant throughout the catalyst layer. The results indicate that the thermal efficiency is enhanced by appropriately managing combustor heat, reactant concentration, and inflow rates as implemented by inlet gas control into the main reactor and combustor. A parametric study of operation control variables, such as Steam to carbon ratio (SCR) and combustible reactant ratio, could determine the optimal values for the highest thermal performance.     

Numerical study on the pulsatile flow characteristics of proximal anastomotic models

Haemodynamics was widely believed to correlate with anastomosis restenosis. Utilizing the haemodynamic parameters as indicator functions, distal anastomosis was redesigned by some researchers so as to improve the long-term graft patency rate. However, there were few studies upon the proximal anastomosis. Therefore, in this study, flow characteristics and distributions of the haemodynamic parameters in proximal anastomosis under physiological flow condition have been investigated numerically for three different grafting angles: namely, 45 degrees forward facing, 45 degrees backward facing, and 90 degrees anastomotic joints. The simulation results showed a flow separation region along the graft inner wall immediately after the heel at peak flow phase and it decreased in size with the grafting angle shifting from 45 degrees forward facing to 45 degrees backward facing. At the same time, a pair of vortex was found in the cross-sectional planes of the 45 degrees backward facing and 90 degrees grafts. In addition, stagnation point was found along the graft outer wall with small shifting during the physiological cycle. High spatial and temporal wall shear stresses gradients (WSSG) were observed around the anastomotic joint. Low time-averaged wall shear stress (WSS) with elevated oscillation shear index (OSI) was found near the middle of anastomosis at the aorta wall and along the graft inner wall respectively, while high time-averaged WSS with low OSI was found at the heel, the toe, and the region downstream of the toe. These regions correlated to early lesion growth. Elevated time-averaged WSSG was found at the same region, where the elevated low-density lipoprotein (LDL) permeability was observed as reported in the literature. The existence of nearly fixed stagnating location, flow separation, vortex, high time-averaged WSS with low OSI, low time-averaged WSS with elevated OSI, and high time-averaged WSSG may lead to graft stenosis. Moreover, the simulation results obtained were consistent with those of experimental measurements. Based on the validated simulation results, the 45 degrees backward-facing graft was found to have the lowest variation range of time-averaged WSS and the lowest segmental average of WSSG among the three models investigated. The 45 degrees backward-facing graft is thus recommended for the bypass operation with expected higher patency rate.     

结构化表面环境下软磨粒流的流场数值分析

为了研究模具结构化表面环境下软性磨粒流的流场加工特性,应用单颗动力学模型(SPD)通过数值模拟求解了颗粒在不同形态的湍流场中的运动特性.以U形流道为例,利用N-S方程、湍流的Realizable(k-ε)模型以及压力耦合方程的半隐相容(SIMPLEC)算法,求解了软性磨粒两相流场中流体的速度、压力等特性参数;接着利用S...     

角接触球轴承动特性的数值与试验研究

角接触球轴承的动特性对机床主轴的回转精度、可靠性及寿命等有重要影响。以弹性力学理论、滚动轴承动力学和沟道控制理论为基础,研究角接触球轴承的动特性。推导了计及过盈配合量和预紧力影响的高速角接触球轴承动刚度计算方法,并对轴承动刚度的影响因素进行了理论分析和试验验证。结果表明:随着过盈量的增大,轴向刚度逐渐减小,径向刚度则逐渐增大,外圈过盈量影响更显著;预紧力过小时,刚度会出现明显的波动现象,适当的预紧力对角接触球轴承刚度的稳定至关重要。     

Numerical study on flow and heat transfer characteristics of air-jet cooling system

Journal of Mechanical Science and Technology - The present study aims to numerically analyze the cooling characteristics of the air-jet array in designing more efficient air-cooling system. Heat...     

三相磨粒流抛光及其气泡溃灭分布特性

针对软性磨粒流在加工硬脆性材料时效率低下的问题,本文提出一种气-液-固三相磨粒流加工方法。该方法通过在加工流场内注入微尺度气泡群,利用气泡溃灭释放的能量提升磨粒流加工能力。基于计算流体力学和群体平衡模型耦合计算方法,建立气-液-固三相磨粒流流体力学模型,数值模拟结果揭示了工件表面三相磨粒流形成高速湍流涡旋流场加工特性,得到了工件表面气泡溃灭的分布规律,并探明流体黏度与气泡溃灭之间的关系。图像粒子测速实验表明,通入微尺度气泡群后,平均速度从12.50~13.50m/s提升至15.00~17.00m/s,最高平均速度可达20.00m/s以上。对比加工实验显示,经8h加工后,粗糙度从0.50μm降低到0.05μm。理论和实验研究结果说明借助微尺度气泡群的溃灭效应可有效提升软性磨粒流的加工效率和加工精度。     

微磨料汽雾超声抛光加工技术及实验研究

提出了一种新型精密抛光加工方法,即用含有微磨料的抛光液经超声振动使之雾化形成汽雾流,用此含有微磨料的汽雾流冲蚀工件表面而去除工件材料。通过产生汽雾流的超声振动分析和实验对这一微磨料汽雾超声抛光加工技术进行了研究。结果表明:这一方法可以实现对工件表面的抛光处理,而且比传统的抛光加工方法具有加工冲蚀力更柔软、加工质量更好,并且没有喷嘴损耗等优点。     

Study and evaluation of abrasive water jet cutting performance on AA5083-H32 aluminum alloy by varying the jet impingement angles with different abrasive mesh sizes

This article describes the experimental investigation of abrasive water jet (AWJ) cutting on AA5083-H32 aluminum alloy. In this study, the influence of varying the jet impingement angles and abrasive mesh sizes with different water jet pressures, on the output parameters for the AWJ cutting of the aluminum alloy, was analyzed. The experimental results found that the output parameters, namely, the depth of penetration, top kerf width, kerf taper ratio, surface roughness, and abrasive contaminations, were strongly influenced by the combined effect of oblique jet impingement angles and abrasive mesh sizes on AWJ. Also, it is noticed that oblique jet impingement angles have more influence on the output cutting responses than the normal jet impingement angle, and consequently, each abrasive mesh size has an influence on the different output responses for the AWJ cutting of AA5083-H32. Scanning electron microscope and microhardness tester were used to examine the different cutting regions of the kerf wall surfaces. The Energy-dispersive X-ray spectroscopy analysis was used to confirm the amount of silicon particles embedded in the AWJ cut surfaces. The adequacy checking of the experimental data for the AWJ cutting performance models has been analyzed through the residual plots using the statistical software.     

螺旋槽管内传热及阻力特性的数值研究

为了深入分析螺旋槽管内传热及阻力特性,基于Fluent对16根具有不同结构参数的单头螺旋槽管进行了数值研究。分析了雷诺数Re、槽深e和螺距p对螺旋槽管内传热及阻力特性的影响,结果表明,在研究的雷诺数Re范围内(10000~45000),螺旋槽管的努塞尔数Nu是光管的1.34~2.01倍,且随Re的增加而增加;阻力系数f是光管的2.01~6.40倍,随Re的增加而减小;Nu和f随e的增加而增加,随p的增大而减小。通过回归分析,得到了螺旋槽管传热和阻力的准则关联式,供相关工程设计参考。     

安全阀开启流场机理的数值仿真与实验研究

该文结合ANSYS CFX动网格技术和CEL编译语言创建了安全阀瞬态动力学运动方程,将开启部件的位移与动网格关联,采用数值模拟的方法研究安全阀开启瞬态动力学问题,分析和讨论了开启过程中的流场参数间的影响机理,数值模拟流场机理结果显示安全阀的流场参数在不同时刻和不同的空间位置上存在突变点,最后采用自行设计的安全阀开启实验检测装置对开启流场的流场参数进行实时采集,模拟和实验数据对比分析的研究结果吻合较好,说明该文提出瞬态开启数值模拟方法和实验系统,应用于安全阀超压泄放机理研究中是具有可行性的。     

A study on the combustion characteristies of coaxial jet furnaces with swirl flow

This study is an analysis of the turbulent diffusion flame with swirl flow and the calculated results are compared with experimental data in cases of various swirl numbers and air-fuel ratios. The mathematical model is restricted to single-phase, diffusion controlled combustion with swirl flow. Values of local flow properties are obtained by solving appropriate differential equation for continuity, momentum, stagnation enthalpy, concentration, turbulence energy, dissipation rate of turbulence energy, and the mean square of concentration fluctuation. The method is proposed for calculating the local probability of chemical reaction on the use of the probability density function for the mixture fraction.