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本文从描述多维湍流气固两相流的两流体模型出发,导出了计算湍流气固两相流中固体颗粒扩散速度的计算模型,进而基于在一维流场中颗粒的终端速度是重力加速度gi的函数,提出在多维流场中颗粒相处于一个修正的加速度场g'i的作用下,该修正的加速度g'i包含了包括重力在内的各种力的作用,这些力对颗粒的加速作用与重力对颗粒的加速作用没有区别。根据这种观点,提出了用于模拟多维湍流气固两相流的改进的扩散模型。本文使用改进的扩散模型对台阶后方的气固两相流进行了数值模拟,并将数值计算结果与实验结果进行了比较,结果表明,改进的扩散模型的预报结果与实验结果符合得相当好。 相似文献
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为研究聚变堆氚增殖包层中液态金属湍流磁流体动力学(MHD)效应,开发了一种新的准二维单方程
MHD 湍流模型,并进行了相关数值模拟程序的编制及验证。对于矩形管道中的准二维 MHD 湍流流动,三维流
动主要发生在哈德曼层中,中心的主流区呈现出二维流动。为了反映这种特殊的流动特征,新湍流模型在标准 k-ε
模型的基础之上去掉了传统的耗散项,代之以电磁耗散项来模拟湍流 MHD 效应。同时,采用 Bradshaw 假设来对
湍流涡粘系数进行模化。为验证该湍流模型是否合理,编制了相关数值模拟程序,并利用直接数值模拟(DNS)结
果对该程序进行了校正,数值模拟结果与 DNS 结果吻合较好。计算结果表明,该湍流模型可应用于聚变堆液态
包层 MHD 湍流流动的数值模拟。 相似文献
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尽管目前湍流两相燃烧(液雾和固体燃料燃烧)的数值模拟在国内外已经有雷诺平均模拟(RANS模拟)、大涡模拟(LES)和点源颗粒的直接数值模拟(Point-Particle DNS)的不少研究结果,但是仍然存在不少尚待解决的问题。本文就作者对目前研究状况的了解和认识,提出在基础研究和数值模拟方面的研究需求,供有关研究者参考。 相似文献
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Freddy Sthlberg Jens Mogelvang Carsten Thomsen Bo Nordell Max Stubgaard Anders Ericsson Gran Sperber Dan Greitz Henrik Larsson Ole Henriksen Bertil Persson 《Magnetic resonance imaging》1989,7(6):655-667
The aim of this study was to establish a rapid method for in vivo quantification of a large range of flow velocities using phase information. A basic gradient-echo sequence was constructed, in which flow was encoded along the slice selection direction by variation of the amplitude of a bipolar gradient without changes in sequence timings. The influence of field inhomogeneities and eddy currents was studied in a 1.5 T scanner. From the basic sequence, interleaved sequences for calibration and in vivo flow determination were constructed, and flow information was obtained by pairwise subtraction of velocity-encoded from velocity non-encoded phase images. Calibration was performed in a nongated mode using flow phantoms, and the results were compared with theoretically calculated encoding efficiencies. In vivo flow was studied in healthy volunteers in three different areas using cardiac gating; central blood flow in the great thoracic vessels, peripheral blood flow in the popliteal vessels, and flow of cerebrospinal fluid (CSF) in the cerebral aqueduct. The results show good agreement with results obtained with other techniques. The proposed method for flow determination was shown to be rapid and flexible, and we thus conclude that it seems well suited for routine clinical MR examinations. 相似文献
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烟用有机肥中氯离子含量测定方法的比较 总被引:2,自引:0,他引:2
为科学指导烟草栽培中有机肥的施用,以保证烟叶氯含量在适宜范围内,保障烟叶质量,研究比较了离子色谱法、连续流动分析法、硝酸银滴定法和佛尔哈德法测定烟用有机肥中氯离子含量.几种测定氯离子含量的方法比较结果为:离子色谱法和连续流动分析法测定烟用有机肥中氯离子含量的结果均较好,且方法不存在显著差异;硝酸银滴定法对低含量样品的检测偏差较大;佛尔哈德法不适宜用于测定烟用有机肥中氯离子含量.离子色谱法和连续流动分析法的平均回收率分别为102.4%、103.1%,方法检出限分别为0.05mg/L、0.30mg/L,对样品测定的平均相对标准偏差分别为2.41%和2.77%. 相似文献
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数值模拟研究了高速气流作用下激光加热金属平板温度场。流体控制方程为三维雷诺平均Navier-Stokes方程,固体控制方程为能量方程,湍流粘性系数求解使用k-ε两方程模型。采用流固耦合计算方法,使用两相流模型模拟气流对烧蚀物的剥蚀,较完整地模拟了激光辐照金属材料的物理变化过程,计算得到了不同气流速度下金属平板的温度分布以及烧蚀形貌。分别使用两相流方法和动网格方法对高速气流作用下激光对金属板的烧蚀效应进行了计算,结果表明,两相流方法与动网格方法都能较好地模拟高速气流作用下激光加热金属平板的温度响应,由于两相流方法能够较全面地模拟对流换热、熔化与凝固过程以及金属液体在气流冲刷下的动力学过程,因此能获得比动网格方法更为合理的物理图像。 相似文献
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L. Goubergrits S. Weber Ch. Petz H-Ch. Hege A. Spuler J. Poethke A. Berthe U. Kertzscher 《显形杂志》2009,12(3):241-250
Flow visualization of a near wall flow is of great importance in the field of biofluid mechanics in general and for studies of pathologic vessel enlargements (aneurysms) particularly. Wall shear stress (WSS) is one of the important hemodynamic parameters implicated in aneurysm growth and rupture. The WSS distributions in anatomically realistic vessel models are normally investigated by computational fluid dynamics (CFD). However, the results of CFD flow studies should be validated. The recently proposed Wall-PIV method was first applied in an enlarged transparent model of a cerebri anterior artery terminal aneurysm made of silicon rubber. This new method, called Wall-PIV, allows the investigation of a flow adjacent to transparent surfaces with two finite radii of curvature (vaulted walls). Using an optical method which allows the observation of particles up to a predefined depth enables the visualization solely of the boundary layer flow. This is accomplished by adding a specific molecular dye to the fluid which absorbs the monochromatic light used to illuminate the region of observation. The results of the Wall-PIV flow visualization were qualitatively compared with the results of the CFD flow simulation under steady flow conditions. The CFD study was performed using the program FLUENT®. The results of the CFD simulation were visualized using the line integral convolution (LIC) method with a visualization tool from AMIRA®. The comparison found a very good agreement between experimental and numerical results. 相似文献
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非设计工况下动静叶相互干扰的非定常流动特性 总被引:2,自引:0,他引:2
本文对非设计工况下动静叶栅相互干扰的非定常流动特性进行数值研究。非设计工况主要考虑大攻角下的分离 流动,动静叶干扰的非定常流动的数值求解在N—S方程的基础上采用分区计算的方法来完成。数值分析结果揭示了在分 离流动本身的非定常特性与动静叶栅相互干扰的非定常特性的双重影响下的流场情况。 相似文献
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提出了一种考虑碳烟颗粒的气氧煤油发动机尾焰红外辐射特性计算方法,首先对气氧煤油发动机纯气相内流场进行计算,然后以喷管喉部作为气体和固体碳烟颗粒的入口边界计算发动机尾焰流场,最后以发动机流场参数分布为基础,采用有限体积法和伪气体理论对发动机尾焰红外辐射特性进行计算。进行了气氧煤油发动机点火实验,并将计算结果与实验结果进行对比分析。结果表明,燃烧室内两个压力测量点的测量与计算误差分别为1.4%和3.4%,燃烧室内计算温度与热力学计算误差为2.16%,证明了燃烧室流场计算模型的准确性。含有碳烟颗粒的尾焰流场计算结果与热像仪测量结果比较吻合,证明了尾焰流场计算方法和模型的准确性。4.3 μm波段尾焰红外成像计算结果与工作在4.3 μm波段的红外热像仪测量结果吻合比较一致,证明了尾焰红外辐射特性计算方法和模型的准确性。 相似文献
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为了解决光流跟踪法定位精度不足、误差累积和特征点匹配法耗时久的问题,设计了一种将随机抽样一致性(random sample consensus,RANSAC)光流跟踪法和改进的特征点匹配法结合的视觉里程计。利用RANSAC光流跟踪法对关键帧之间的小规模运动进行估计,RANSAC算法对光流跟踪的误匹配点进行剔除,大大降低了光流跟踪法存在的误匹配;而关键帧之间的运动估计则利用改进的特征点匹配法,以修正光流跟踪法的估计误差;最后利用卡尔曼滤波将RANSAC光流跟踪法和改进的特征点匹配法进行融合。实验结果表明:该文的算法能够克服光流跟踪法精度不足、误差累积的问题,将平均相对误差由15.5%提升到了2.6%;同时也能在一定程度上提高特征点匹配法的速度,将特征点匹配法的平均耗费时间由37.28 ms提升到了21.07 ms。 相似文献
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轴流叶轮机械三维非定常粘性流动数值分析 总被引:5,自引:0,他引:5
1前言叶轮机内部流动的数值计算方法一般都是基于转子与静子结构相互无关的定常流动假设,这种假设实际上是认为转子叶排与静子叶排相距足够远,以至于相互之间互不干扰。事实上,叶轮机中的非定常性是其固有的,转子叶排与静子叶排相距很近,转子叶排的高速旋转、上游叶... 相似文献
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In this study, the behavior of a single bubble in a dielectric viscous fluid under a uniform magnetic field has been simulated numerically using the Level Set method in two-phase bubbly flow. The two-phase bubbly flow was considered to be laminar and homogeneous. Deformation of the bubble was considered to be due to buoyancy and magnetic forces induced from the external applied magnetic field. A computer code was developed to solve the problem using the flow field, the interface of two phases, and the magnetic field. The Finite Volume method was applied using the SIMPLE algorithm to discretize the governing equations. Using this algorithm enables us to calculate the pressure parameter, which has been eliminated by previous researchers because of the complexity of the two-phase flow. The finite difference method was used to solve the magnetic field equation. The results outlined in the present study agree well with the existing experimental data and numerical results. These results show that the magnetic field affects and controls the shape, size, velocity, and location of the bubble. 相似文献