Accuracy of theoretical models in the prediction of solar chimney performance

A solar chimney is a solar power plant which generates mechanical energy (usually in terms of turbine shaft work) from a rising hot air that is heated by solar energy. The present paper compares the predictions of performances of solar chimney plants by using five simple theoretical models that have been proposed in the literature. The parameters used in the study were various plant geometrical parameters and the insolation. Computational Fluid Dynamics (CFD) simulation was also conducted and its results compared with the theoretical predictions. The power output and the efficiency of the solar chimney plants as functions of the studied parameters were used to compare relative merits of the five theoretical models. Models that performed better than the rest are finally recommended.     

Transient supersonic release of hydrogen from a high pressure vessel: A computational analysis

Understanding the characteristics of a hydrogen gas jet exiting from a compressed vessel during vessel rupture or venting is crucial for determining safety requirements for distribution and use of hydrogen. Such jets can undergo several flow regimes during venting, from initial supersonic flow, to transonic, to subsonic flow regimes as the pressure in the vessel decreases. A bow shock wave is a characteristic flow structure during the initial stage of the jet development, and this paper focuses on the development of the bow shock wave and the jet structure behind it. The transient behaviour of an impulsively initiated jet is investigated using unsteady, compressible flow simulations. Both the cases of a hydrogen jet exiting into quiescent hydrogen and of a hydrogen jet exiting into air are presented. The gases are considered to be ideal, and the computational domain is axisymmetric. The jet structure, including the shock wave and flow separation due to an adverse pressure gradient at the nozzle is investigated with a focus on the differences between the single- and multi-component flow scenarios.     

三例人体颈动脉分叉管血液动力学的数值对比分析

颈动脉粥样硬化的发生常常呈现出强烈的几何选择性特征,表明其几何形状对局部血液动力学特征影响很大.本研究采用Mimics软件对三例真实人体颈动脉分叉管的CT影像数据进行了图像处理,重建了三维几何模型.对三种不同出口流量分配比条件下的脉动血液流场进行了全三维数值模拟,重点分析了流量分配比和分叉管几何特征对局部血液动力学的影响.计算结果表明:(1) 内外颈动脉血液流量分配比的变化对颈动脉分叉管内的血液动力学特征影响很大,但具体程度因颈动脉形状差异而不同;(2) 颈动脉分叉角或颈动脉窦较大时,颈动脉分叉处流动比较紊乱,低速区和低壁面剪应力区面积较大,使得粥样硬化风险较高.     

Numerical simulation of a liquid propellant rocket motor

IntroduedonModelling and numerical simulation are presentedin nearly every aspect of aerospace engineeringnowadays thanks to availability of powerful andrelatively inexpensive computing tools. This workpresents a numerical simulation of the flow field in aliquid Propellant rocket engine chamber and exit nozZleusing techniques to allow the results to be taken asstaring points for designing those PrOPulsive systems.iiis was dolle using a Finite VolUme method sthe different flow regimes which …     

Computational Fluid Dynamics (CFD) Modeling of Gaseous Pollutants Dispersion in Low Wind Speed Condition: Isfahan Refinery,a Case Study

A 3D computational fluid dynamics (CFD) model is developed to predict the dispersion of gaseous pollutants released from different stacks in Isfahan refinery in Iran. Three types of turbulent models including the standard k–?, the RNG k–?, and the realizable k–? models are compared and considered. The results of model are compared with the experimental data obtained by measuring the CO₂ concentration inside and close to the refinery boundaries. The comparison shows the sufficient precision of model predictions. By using the design of experiment (DOE) technique, the effects of model parameters are investigated on the results. The results of standard k–? model for Sc _t = 0.5 and h_r = 2 m, the realizable k–? model for h_r = 2 m, and the RNG.k–? model for h_r = 2.5 m provide more acceptable results when these results are compared with the models responses with ideal values of these parameters. The latter gives some better results for the case of Isfahan refinery.     

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...     

自主水下航行器折叠天线设计

通过对水下机器人的主体外形以及传统水下机器人的外附体进行建模,运用CFD流体软件对其进行仿真分析,发现自主水下航行器外附体中,天线产生阻力最大.天线是自主水下航行器必不可少的通信模块.针对天线带来的大阻力问题,设计出两种折叠天线机构.运用ADAMS软件对比了两种折叠天线机构运动性能参数;运用SolidWorks的应力仿...     

水下压缩空气储能系统储气装置的CFD数值模拟

针对水下储气装置在复杂的海洋环境中容易受到海流的影响从而引发结构失效等问题,采用大涡模拟方法,对不同海流条件下的水下储气装置流体动力学特性进行了数值模拟.首先对比分析了不同流速工况下海水绕流后的时均速度场;其次通过监测在0.5 m/s流速工况下旋涡的发展及脱落过程以研究尾迹流场的瞬态变化情况;最后分析了在不同工况下装置...     

基于CFD动网格优化快速锻造机补液模型研究

随着汽车行业的发展,汽车对金属材料的加工要求越来越高,尤其对车轴的金属质量和加工精度提出了更加严格的要求.目前加工车轴的快速锻造机,采用充液罐进行补液,此方式无法实现高质量和高精度的加工.使用充液罐补液存在两个不足:一是充液罐压力低,滑块在下行接触工件后,液压油流速低,补液时间较长,建压缓慢,导致工作效率低;二是液压缸...