共查询到19条相似文献,搜索用时 546 毫秒
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研究多相介质运动的意义、内容和方法 总被引:2,自引:0,他引:2
本文从连续介质假设、守恒方程、本构关系和固壁上的边界条件等方面的分析出发,指出二相流体动力学虽是流体力学的一个分支,但在研究内容上与流体力学有较大差异,从分析二相流特点与稀薄气体、稠密气体、非平衡流动和可压缩流动特点之间的相似性出发,指出二相流研究可借鉴相关学科的研究成果和研究方法。本文用弛豫时间概念解释了二相混合物与均相混合物在运动特征上的差异,以及在描写运动的方法上(双流体模型和单流体模型等)的相应差异。最后以风沙运动、泥沙运动和泥石流运动为例,说明在二相流研究中突出主要因素进行合理简化的重要性,并指出:对于不同类型的二相流、对于具有不同流动参数的同类二相流、对于同一二相流的不同区域或不同的研究目的,简化的方法都会有所不同。 相似文献
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关于二相流、多相流、多流体模型和非牛顿流等概念的探讨 总被引:10,自引:0,他引:10
本文分析了单相流、二相流和多相流等概念上的差异,也分析了单流体模型、双流体模型和多流体模型等概念上的差异,指出前面三种概念是按流动介质的客观物理构成划分的,而后者是按主观采用的研究方法划分的.目前这些概念在使用中存在一些混乱,如二相流与多相流,多相流与多流体模型等.本文还研究了扩散模型、非牛顿流模型和颗粒流模型等,指出前两种模型在分类上属于单流体模型,分析了非牛顿流模型、扩散模型和双(多)流体模型的特点和应用范围,最后,以泥石流为例讨论了以上概念的应用. 相似文献
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两相流中密度波现象的研究及进展 总被引:4,自引:1,他引:4
密度波(又称连续波、空隙度波、运动学波)是两相流中的特殊现象,本文评述两相流密度波理论的主要研究进展,这些理论不仅研究了线性密度波和非线性密度波的特性,还研究了气液两相流的流型转变与密度波的关系,流化床中气塞的形成和床层的塌陷现象与密度波的关系等.同时介绍试验和理论研究在密度波的波速、频率、稳定性和色散性等方面取得的主要结论.最后指出密度波的理论和试验研究尚需进一步解决的问题. 相似文献
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水气二相流与诸多领域的实际工程问题密切相关. 对二相流运动进行高精度的数值模拟是计算流体力学研究的难点和热点. 针对开敞水域的自由表面流运动问题, 将水和空气均视为不可压缩流体, 采用五阶加权基本无震荡(weighted essentially non-oscillatory, WENO)格式求解描述流体运动的纳维斯托克斯(Navier-Stokes, NS)方程, 利用以加权线性界面算法改进的多维双曲正切函数界面捕捉法(tangent of hyperbola for interface capturing with weighed line interface calculation, THINC/WLIC)追踪水气界面, 建立WENO-THINC/WLIC水气二相流运动数值模型. 模型采用分步计算法离散求解控制方程, 通过压力投影法求解压强场, 并利用三阶总变差递减(total variation diminishing, TVD)龙格库塔(Runge-Kutta, RK)法对时间项进行离散求解. 通过对环境速度场下Zalesak's disk和shearing vortex界面运动问题, 线性液舱晃荡问题以及溃坝问题的模拟结果与理论分析或试验结果的比较, 对所建立的水气二相流数值模型的适用性及模拟精度进行了验证. 结果表明, 本模型的模拟结果与物理模型或理论分析结果吻合良好, 能较为准确地再现不可压缩水气二相流运动现象. 鉴于WENO格式和THINC法本身在算法及应用等方面仍在不断改进, 本研究提出的WENO-THINC耦合模型为后续更高精度的二相流计算模型开发提供了一种研究思路. 相似文献
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对空气-油在垂直下降管中的流型进行了实验研究,采用的管径为29mm,油和空气的折算流速分别达到4m/s和20m/s,并借助于压降脉动分析和目测观察相结合的方法来进行流型的识别。研究表明,油气两相流的流型不同于低粘液体的两相流流动,通过实验研究并结合前人的研究成果,给出了液相粘度对流型转变的影响趋势。 相似文献
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水下气水两相射流流态的实验研究 总被引:1,自引:0,他引:1
在模拟水池中进行了水下气水两相射流流态的观察,研究了不同引射条件下,水下气泡的生成和扩散规律,对于珍贵水产养殖中人工增氧方法的改善有很大意义. 相似文献
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柱体形状对气液两相涡街的影响 总被引:4,自引:0,他引:4
本文试验研究了柱体形状对气液两相涡街的影响,得出了在气液两相流中的最佳涡街发生体和发生两相涡街时,两相斯托拉赫数,来流截面含气率,水流量三者之间的关系。试验工质为水和空气,混合物流动方向垂直向上。参数范围:相对压强0.0-0.2MPa;来流截面含气率0.0-0.35;水流量0.0-26m3/h。 相似文献
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Theoretical studies have been made to determine the pressure drops caused by abrupt flow area expansion/contraction in small circular pipes for two‐phase flow of air and water mixtures at room temperature and near atmospheric pressure. Two‐phase computational fluid dynamics (CFD) calculations, using Eulerian–Eulerian model (with the air phase being compressible for pipe contraction case) are employed to calculate the pressure drop across sudden expansion and contraction. The pressure drop is determined by extrapolating the computed pressure profiles upstream and downstream of the expansion/contraction. The larger and smaller tube diameters are 1.6 and 0.84 mm, respectively. Computations have been performed with single‐phase water and air, and two‐phase mixtures in a range of Reynolds number (considering all‐liquid flow) from 1000 to 12 000 and flow quality from 1.2 × 10?3 to 1.6 × 10?2. The numerical results are validated against experimental data from the literature and are found to be in good agreement. The expansion and contraction loss coefficients are found to be different for single‐phase flow of air and water, and they agreed reasonably well with the commonly used theoretical predictions. Based on the numerical results as well as experimental data, correlations are developed for two‐phase flow pressure drops caused by the flow area contraction as well as expansion. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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This paper presents the extension of a high‐resolution conservative scheme to the one‐dimensional one‐pressure six‐equation two‐fluid flow model. Only mixtures of water and air have been considered in this study, both fluids have been characterized using simple equations of state, namely stiffened gas for the liquid phase and perfect gas for the gas phase. The resulting scheme is explicit and first‐order accurate in space and time. A second‐order version of the scheme has also been derived using the MUSCL strategy and slope limiters. Some numerical results show the good capabilities of this type of schemes in the solution of discontinuities in two‐fluid flow problems, all of them are based on water/air numerical benchmarks widely used in the two‐phase flow literature. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Zhihua Xie 《国际流体数值方法杂志》2012,70(2):246-268
A two‐phase flow model, which solves the flow in the air and water simultaneously, is presented for modelling breaking waves in deep and shallow water, including wave pre‐breaking, overturning and post‐breaking processes. The model is based on the Reynolds‐averaged Navier–Stokes equations with the k ?ε turbulence model. The governing equations are solved by the finite volume method in a Cartesian staggered grid and the partial cell treatment is implemented to deal with complex geometries. The SIMPLE algorithm is utilised for the pressure‐velocity coupling and the air‐water interface is modelled by the interface capturing method via a high resolution volume of fluid scheme. The numerical model is validated by simulating overturning waves on a sloping beach and over a reef, and deep‐water breaking waves in a periodic domain, in which good agreement between numerical results and available experimental measurements for the water surface profiles during wave overturning is obtained. The overturning jet, air entrainment and splash‐up during wave breaking have been captured by the two‐phase flow model, which demonstrates the capability of the model to simulate free surface flow and wave breaking problems.Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Experimental and numerical analysis of two-phase infiltration in a partially saturated soil 总被引:9,自引:0,他引:9
The purpose of this study is to analyze the effects of the soil air flow on the process of water infiltration in a 93.5 cm deep vertical column for varied boundary conditions at the surface - positive time constant head; time constant fluxes smaller and greater than saturated soil hydraulic conductivity.Several experiments conducted on a sandy soil column with and without a possible air flow through the wall are presented. Continuous and simultaneous measurements of water content and air and water pressure heads at different depths allow the analysis of the air and water movements within the soil and the determination of the capillary pressure and relative permeability for each phase as functions of the volumetric water content.A numerical solution of the equations describing the simultaneous flow of air and water is compared with the experimental data and with the traditional one-phase flow modeling. The results show that the air movement may significantly affect water flow variables such as infiltration rates, water content profiles, and ponding times.Furthermore, some basic assumptions used in two-phase flow modeling, such as the hydrodynamic stability of the wetting fronts and the pertinence of the relative permeability concept, are discussed in the light of the experimental data. 相似文献
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A closed container with gas and liquid inflows and one outlet for outflow, described by a nonlinear hydraulic model, is shown to reach a state of sliding mode. Through a Lyapunov function, the sliding motion is shown to be stable for all positive exponents in the flow model. This property is independent of factors such as valve opening, valve coefficients, friction factor and initial states, making this device a suitable one to study two phase flow. The sliding solution of this system, with square root hydraulic model, is found using Filippov's equivalent dynamic approach. The discontinuous system is also solved using an accurate and efficient method that accounts for persistent discontinuity sticking. These two solutions are shown to be in exact agreement. 相似文献
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Development of temporal and spatial high‐order schemes for two‐fluid seven‐equation two‐pressure model and its applications in two‐phase flow benchmark problems 下载免费PDF全文
Current existing main nuclear thermal‐hydraulics (T‐H) system analysis codes, such as RALAP5, TRACE, and CATHARE, play a crucial role in the nuclear engineering field for the design and safety analysis of nuclear reactor systems. However, two‐fluid model used in these T‐H system analysis codes is ill posed, easily leading to numerical oscillations, and the classical first‐order methods for temporal and special discretization are widely employed for numerical simulations, yielding excessive numerical diffusion. Two‐fluid seven‐equation two‐pressure model is of particular interest due to the inherent well‐posed advantage. Moreover, high‐order accuracy schemes have also attracted great attention to overcome the challenge of serious numerical diffusion induced by low‐order time and space schemes for accurately simulating nuclear T‐H problems. In this paper, the semi‐implicit solution algorithm with high‐order accuracy in space and time is developed for this well‐posed two‐fluid model and the robustness and accuracy are verified and assessed against several important two‐phase flow benchmark tests in the nuclear engineering T‐H field, which include two linear advection problems, the oscillation problem of the liquid column, the Ransom water faucet problem, the reversed water faucet problem, and the two‐phase shock tube problem. The following conclusions are achieved. (1) The proposed semi‐implicit solution algorithm is robust in solving two‐phase flows, even for fast transients and discontinuous solutions. (2) High‐order schemes in both time and space could prevent excessive numerical diffusion effectively and the numerical simulation results are more accurate than those of first‐order time and space schemes, which demonstrates the advantage of using high‐order schemes. 相似文献
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由空压机提供的气体通过—排微小直径的喷嘴进入静止水体,形成水气两相流流场。在单相PIV和PTV技术的基础上,研究稀疏气液两相流情况下气泡的速度场分布。PIV算法采用快速傅立叶互相关分析法,而PTV算法需要获得每幅图像中每个气泡的形心,根据连续图像中的粒子对,计算速度。用PIV和PTV两种算法处理求出气泡的速度并对两种方法进行比较,其最终研究成果可应用于流体及多相流的流量测技术,提高我们进行低密度气液两相流相关研究的测量水平。同时为水气两相流的数值分析和理论研究提供流场测试的数据。 相似文献
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Yang‐Yao Niu 《国际流体数值方法杂志》2001,36(3):351-371
In this study, the advection upwinding splitting method (AUSM) is modified for the resolution of two‐phase mixtures with interfaces. The compressible two‐fluid model proposed by Saurel and Abgrall is chosen as the model equations. Dense and dilute phases are described in terms of the volume fraction and equations of state to represent multi‐phase mixtures. Test cases involving an air–water shock tube, water faucet, and dilute particulate turbulent flows through a 90° bend are used to verify the current work. It is shown that the AUSM based on flux differences (AUSMD) contains the mechanism to correctly capture the contact discontinuity and interfaces between phases. In addition, a successful application to dilute particulate turbulence flows by the AUSMD is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献