CFD analysis of a high‐speed unsteady jet

The flow of a high‐speed unsteady jet is analyzed using computational fluid dynamics for an incompressible flow with the k–ε turbulence model. The pseudo‐nozzle concept is applied to the inlet condition with a large pressure gradient. The results show that the time history of the jet development agrees with the experimental data for methane and hydrogen fuels. In addition, the effect of the injection condition on the development of the jet tip is well described with this model. Furthermore, the effects of inlet conditions of the turbulence intensity and scale on the flow are investigated. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 1– 12, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20141     

水平轴风力机的推力型工作原理

在水平轴风力机升力型工作原理的基础上提出一种新的推力型工作原理,提供一项显著提高风力机风能利用系数的桨尖喷气技术,即充分利用传统升力型风力机风轮旋转离心力在除去整流罩的空心轮毂内产生的低压,将轮毂前方的气体吸入,并通过中空的桨叶,再从桨尖处预先设置的切向孔中与旋转方向反向喷出,从而产生推动风轮旋转的“辅助”转矩,并使发电量和风能利用系数大大提高。大量的风洞对比实验证明,桨尖喷气技术可以提高风力机输出功率30%以上。     

窄缝挑坎出流水舌出射角的计算

从窄缝挑坎收缩段水流的连续方程和能量方程入手,推导出了水流出射角的计算公式。分析了影响窄缝挑坎水流的出射角的各种因素,确定了水流出射角计算公式中参数的计算方法,从而能够计算直墙窄缝挑坎出流水舌的出射角。     

船舱通风散热系统的数学建模

通过对船舱通风散热系统的传热传质分析,建立了船舱通风散热系统的数学模型,同时为了对该系统进行控制,建立了具体的控制方程。为解决船舶系统的节能问题提供参考。     

地下高大空间火灾烟气自由填充试验研究

利用费诺德(Froude number)相似模型理论,建立1∶12的某地下高大空间(高大空间为高度大于10 m,体积大于10 000 m~3)比例模型,研究了地下高大空间火灾烟气自由填充过程及温度变化特性。1∶12模型试验结果和火灾动力学模拟(fire dynamics simulator,FDS)模拟值与McCaffrey预测值吻合度较高。1∶12火灾模型试验能较好的预测地下大空间烟气流动特点,且是验证数值结果正确性的重要手段。试验表明:高大空间"蓄烟效应"显著,火灾发生时高大空间竖向温度呈线性分布,且温升较小,温度不是影响人员逃生和排烟效果的主要因素;火源位置分别处于模型端部的烟气层下降速度慢于中心位置。该研究为制订火灾排烟和疏散方案及高大空间防排烟规范提供了初步理论依据和第一手的试验资料。     

轴针式喷油嘴喷雾初期发展数学模型的研究

本文通过高速摄影及激光全息摄影研究了轴针式喷油嘴的喷雾发展，指出了在其发展初期可能出现的喷雾轴线偏转等一些不同于孔式喷油嘴喷雾的流动特点。在此实验研究的基础上，根据紊流射流积分方法建立了轴针式喷油嘴喷雾初期发展的数学模型。应用该模型对一普通形喷油嘴及柴油机用ＺＳ４５Ｓ２轴针式喷油嘴喷雾的发展进行了算例分析，计算值与实测值吻合较好。     

Heat transfer augmentation for air jet impinged on a rough surface

An experimental investigation of heat transfer from a round air jet impinging normally from below onto a heated square plate was performed. The objective of the investigation was to study the effect of roughness on both the heat transfer and the fluid flow characteristics. Smooth and rough plates were, therefore, used in the course of the experiments. The heat transfer data were collected for four jet Reynolds numbers, ranging from 6500 to 19 000. The Reynolds numbers are based on the jet-exit velocity (U_e) and the nozzle-exit diameter (D), Re_e=U_eD/ν. The nozzle-to-plate distance ranged from 0.05 to 15 nozzle-exit diameter to cover both the potential core and the far regions of the jet flow. The roughness was composed of cubes of 1 mm dimension distributed uniformly along the plate. The local and average Nusselt number values for the rough plate showed an increase ranging from 8.9% to 28% over those for the smooth plate. Roughness was found to have a strong effect on the flow characteristics; it affected the mean velocity as well as the turbulence intensity of the flow. The mean velocity profiles for the smooth case at radial distances of r/D=1 and r/D=2.5 showed steeper near-wall velocity gradients compared with the profiles of the rough case, where r is the radial distance measured from the plate center along the plate centerline. In addition, roughness caused an increase in the turbulence intensity of the flow.     

粗糙表面流动与换热的数值模拟的新模型

考虑“粗糙元高度”和“粗糙元间距”两个因素的影响，对Van Drist阻尼函数进行了改进，然后将其引入边界层计算程序，对不同粗糙远间距、不同来流速度等工况下粗糙表面的换热进行了计算，结果与实验数据符合良好，说明改进后的Van Drist阻尼函数很好地反映了粗糙度雷诺数及粗糙元分布疏密度的影响，能适用于计算粗糙表面上的流动及换热。     

Spatial and radiative properties of an open-flame hydrogen plume

Considerable effort is being directed toward updating safety codes and standards in preparation for production, distribution, and retail of hydrogen as a consumer energy source. In the present study, measurements were performed in large-scale, vertical flames to characterize the dimensional and radiative properties of an ignited hydrogen jet. These data are relevant to the safety scenario of a sudden leak in a high-pressure hydrogen containment vessel. Specifically, the data will provide a technological basis for determining hazardous length scales associated with unintended releases at hydrogen storage and distribution centers. Visible and infrared video and ultraviolet flame luminescence imaging were used to evaluate flame length, diameter and structure. Radiometer measurements allowed determination of the radiant heat flux from the flame. The results show that flame length increases with total jet mass flow rate and jet nozzle diameter. When plotted as a function of Froude number, which measures the relative importance of jet momentum and buoyancy, the measured flame lengths for a range of operating conditions collapse onto the same curve. Good comparison with hydrocarbon jet flame lengths is found, demonstrating that the non-dimensional correlations are valid for a variety of fuel types. The radiative heat flux measurements for hydrogen flames show good agreement with non-dimensional correlations and scaling laws developed for a range of fuels and flame conditions. This result verifies that such correlations can be used to predict radiative heat flux from a wide variety of hydrogen flames and establishes a basis for predicting a priori the characteristics of flames resulting from accidental releases.     

An Exact Solution for Heat Transfer of a Jet Co-Axially Impinging on a Rotating Disk and Its Comparisons with Stagnation Point Experiments

IntroductionJet impingement is a widely used high-efficiencytechnique fOr cooling rotating disks, which are end-wallsurfaces of gas turbine rotors, comPuter disk drives etc.Fluid f'low, heat trallsfer and geometric arrangement inthe case of a single round jet impinging co-axially in anorthogonal mode on a rotatng disk are characterized byFig. l.Many peculiarihes of fluid fIow and heat transfer ofreal impinging jets under comPlicated conditions(different system geometry, impinging flow proper…