共查询到20条相似文献,搜索用时 31 毫秒
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空隙率波是气液两相流系统的特殊物理现象,理解空隙率波的传播特性对揭示两相流流型转变与流速测量物理机理具有重要意义.本文首先考察了典型非线性系统的多尺度互相关特性,发现去趋势互相关分析方法可有效揭示系统的多尺度非线性动力学特征;然后,通过采集垂直上升小管径气液两相流电导传感器阵列上下游空隙率波动数据,提出采用多尺度去趋势互相关分析方法探测空隙率波传播的多尺度互相关特性,并提取了低尺度空隙率波互相关水平增长率;另外,通过计算空隙率波空间衰减因子,考察了气液两相流空隙率波传播的结构不稳定行为.结果表明,空隙率波结构的多尺度互相关特性与其空间衰减特性具有较好的物理关联性:对于气液两相流过渡流型,低尺度空隙率波互相关水平增长率较高,且与较为稳定的空隙率波传播特性相对应;而当气液两相流空隙率波明显衰减或放大时,空隙率波互相关水平增长速率一般较低. 相似文献
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S. Chibbaro L. Biferale F. Diotallevi S. Succi 《The European physical journal. Special topics》2009,171(1):223-228
We present a systematic study of capillary filling for a binary fluid by using mesoscopic a lattice Boltzmann model describing
a diffusive interface moving at a given contact angle with respect to the walls. We compare the numerical results at changing
the ratio the typical size of the capillary, H, and the wettability of walls. Numerical results yield quantitative agreement with the theoretical Washburn law, provided
that the channel height is sufficiently larger than the interface width and variations of the dynamic contact angle with the
capillary number are taken into account. 相似文献
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A sharp interface Cartesian grid method for the large-eddy simulation of two-phase turbulent flows interacting with moving bodies is presented. The overall approach uses a sharp interface immersed boundary formulation and a level-set/ghost–fluid method for solid–fluid and fluid–fluid interface treatments, respectively. A four-step fractional-step method is used for velocity–pressure coupling, and a Lagrangian dynamic Smagorinsky subgrid-scale model is adopted for large-eddy simulations. A simple contact angle boundary condition treatment that conforms to the immersed boundary formulation is developed. A variety of test cases of different scales ranging from bubble dynamics, water entry and exit, landslide-generated waves, to ship hydrodynamics are performed for validation. Extensions for high Reynolds number ship flows using wall-layer models are also considered. 相似文献
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Gamma-ray densitometry is a frequently used non-invasive method to determine void fraction in two-phase gas liquid pipe flows. Performance of flow meters using gamma-ray attenuation depends strongly on the fluid properties. Variations of the fluid properties such as density in situations where temperature and pressure fluctuate would cause significant errors in determination of the void fraction in two-phase flows. A conventional solution overcoming such an obstacle is periodical recalibration which is a difficult task. This paper presents a method based on dual modality densitometry using Artificial Neural Network (ANN), which offers the advantage of measuring the void fraction independent of the liquid phase changes. An experimental setup was implemented to generate the required input data for training the network.ANNs were trained on the registered counts of the transmission and scattering detectors in different liquid phase densities and void fractions. Void fractions were predicted by ANNs with mean relative error of less than 0.45% in density variations range of 0.735 up to 0.98 gcm−3. Applying this method would improve the performance of two-phase flow meters and eliminates the necessity of periodical recalibration. 相似文献
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Sara Zahedi Katarina Gustavsson Gunilla Kreiss 《Journal of computational physics》2009,228(17):6361-6375
A new model for simulating contact line dynamics is proposed. We apply the idea of driving contact-line movement by enforcing the equilibrium contact angle at the boundary, to the conservative level set method for incompressible two-phase flow [E. Olsson, G. Kreiss, A conservative level set method for two phase flow, J. Comput. Phys. 210 (2005) 225–246]. A modified reinitialization procedure provides a diffusive mechanism for contact-line movement, and results in a smooth transition of the interface near the contact line without explicit reconstruction of the interface. We are able to capture contact-line movement without loosing the conservation. Numerical simulations of capillary dominated flows in two space dimensions demonstrate that the model is able to capture contact line dynamics qualitatively correct. 相似文献
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A. Lévy T. Ceccotti H. Popescu F. Réau P. D’Oliveira P. Monot Ph. Martin J. P. Geindre E. Lefebvre 《The European physical journal. Special topics》2009,166(1):111-116
We present a systematic study of capillary filling for
multi-phase flows by using mesoscopic lattice Boltzmann models describing a diffusive
interface moving at a given contact angle with
respect to the walls. We compare the numerical results at changing
the density ratio between liquid and gas phases, δρ/ρ
and the ratio, δξ/H, between the typical size of
the capillary, H, and the interface width, δξ.
It is shown that numerical results yield quantitative agreement with the
Washburn law when both ratios are large, i.e. as the
hydrodynamic limit of a infinitely thin interface is approached.
We also show that in the initial stage of the filling process, transient behaviour
induced by inertial effects and “vena contracta” mechanisms, may induce
significant departure from the Washburn law.
Both effects are under control in our lattice Boltzmann
equation and in good agreement with the phenomenology of capillary filling. 相似文献
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S. Chibbaro 《The European physical journal. E, Soft matter》2008,27(1):99-106
We present a systematic study of capillary filling for a binary fluid by using a mesoscopic lattice Boltzmann model for immiscible
fluids describing a diffusive interface moving at a given contact angle with respect to the walls. The phenomenological way
to impose a given contact angle is analysed. Particular attention is given to the case of complete wetting, that is contact
angle equal to zero. Numerical results yield quantitative agreement with the theoretical Washburn’s law, provided that the
correct ratio of the dynamic viscosities between the two fluids is used. Finally, the presence of precursor films is experienced
and it is shown that these films advance in time with a square-root law but with a different prefactor with respect to the
bulk interface. 相似文献
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《Journal of computational physics》2008,227(1):763-775
This paper reports a new numerical scheme of the lattice Boltzmann method for calculating liquid droplet behaviour on particle wetting surfaces typically for the system of liquid–gas of a large density ratio. The method combines the existing models of Inamuro et al. [T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase flows with large density differences, J. Comput. Phys. 198 (2004) 628–644] and Briant et al. [A.J. Briant, P. Papatzacos, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion in a liquid–gas system, Philos. Trans. Roy. Soc. London A 360 (2002) 485–495; A.J. Briant, A.J. Wagner, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: I. Liquid–gas systems. Phys. Rev. E 69 (2004) 031602; A.J. Briant, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: II. Binary fluids, Phys. Rev. E 69 (2004) 031603] and has developed novel treatment for partial wetting boundaries which involve droplets spreading on a hydrophobic surface combined with the surface of relative low contact angles and strips of relative high contact angles. The interaction between the fluid–fluid interface and the partial wetting wall has been typically considered. Applying the current method, the dynamics of liquid drops on uniform and heterogeneous wetting walls are simulated numerically. The results of the simulation agree well with those of theoretical prediction and show that the present LBM can be used as a reliable way to study fluidic control on heterogeneous surfaces and other wetting related subjects. 相似文献
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《Revue Generale de Thermique》1996,35(417):592-598
Heat transfer coefficient at vaporisation interface of a two phase capillary loop. In this article, we present the results of heat transfer coefficient measurements at the vaporisation interface of a capillary pumped two-phase loop for two different types of evaporators and various powers. High contact between the evaporator wall and the porous wick, which induces capillary pumping, prevents vapor from escaping and being forced back into the wick and inhibits the device starting up. First, the surface state of the evaporator wall, then the minimum distance between wall and porous wick necessary to optimize operating conditions have been established. 相似文献
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Mechanism for flow-rate controlled breakup in confined geometries: a route to monodisperse emulsions 总被引:1,自引:0,他引:1
This Letter describes a quasistationary breakup of an immiscible, inviscid fluid at low capillary numbers. The breakup proceeds in a coflowing, viscous liquid, in a confined geometry of a long and narrow orifice. In contrast to the capillary instability in an unbounded fluid, the collapse proceeds through a series of equilibria, each yielding the minimum interfacial energy of the fluid-fluid interface. The process is slow in comparison to typical relaxation speeds of the interface, and it is reversible. Its quasistatic character of collapse forms the basis for controlled, high-throughput generation of monodisperse fluid dispersions. 相似文献
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《Journal of Electrostatics》2014,72(6):441-446
An analytical expression for the streaming current in fractal porous media is developed based on the capillary model and the fractal theory for porous media. The proposed fractal model is expressed as a function of the space charge density at the solid–liquid interface, the fluid flow rate, the Debye–Huckel parameter, the minimum and maximum pore/capillary radii and fractal dimensions for porous media. The results are compared with available experimental data and good agreement is found between them. In addition, factors influencing the streaming current in porous media are also analyzed. 相似文献
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基于真实岩心颗粒粒径分布,利用过程法构建疏松砂岩油藏的三维孔隙结构模型,利用相场方法建立两相流体流动数学模型并利用有限元方法进行求解,研究驱替速度、流体性质、润湿性对剩余油分布以及采出程度的影响.结果表明:驱替速度的增大和油水粘度比的减小会导致较大的毛管数,进而有利于采出程度的提高;就润湿性而言,水湿条件下毛管力是水驱油的动力,而在油湿条件下是阻力,因此水湿岩心采出程度更高.同时,从孔隙尺度对油水渗流机理及剩余油分布机理进行揭示,结果表明:由于多孔介质的复杂孔隙结构,流体在流经不同孔隙时呈现不同的流动特征,进而对油水两相流整体的压力分布、流速分布造成重要影响. 相似文献
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M. Dubé C. Daneault V. Vuorinen M. Alava M. Rost 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):15-26
We investigate the structure and dynamics of the interface between
two immiscible liquids in a three-dimensional disordered porous
medium. We apply a phase-field model that includes explicitly
disorder and discuss both spontaneous and forced imbibition.
The structure of the interface is dominated by a length scale
ξ× which arises from liquid conservation. We further show
that disorder in the capillary and permeability act on different
length scales and give rise to different scalings and
structures of the interface properties. We conclude with a
range of applications. 相似文献
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Surface energetic characterization of porous solids usually requires the determination of the contact angle. This quantity is deduced by imbibition experiments carried out in such media with high surface tension liquids. Now then, this methodology needs the geometrical characterization of the porous medium by means of the deduction of its effective radius. Normally, this is made by imbibition experiments with n-alkanes, liquids whose surface tension is low enough as to suppose their contact angles with the solid surface are null. However, this last procedure is not free from some criticisms. Among them, the possible influence of the imbibition velocity on the contact angle, the effect of the precursor liquid film ahead the advancing liquid front on the driving force that gives rise to the movement, or the dependence of the effective radius on the length of the hydrocarbon chain of the n-alkanes. In an attempt of going deeply in these questions, imbibition experiments with n-alkanes have been carried out in porous columns of powdered calcium fluoride. These experiments have consisted of the measurement of the increase in the weight of the columns caused by the migration of the liquids through their interstices. The analysis of their results has been carried out by means of a new procedure based on the study of the velocity profile associated to the weight increase. This analysis has permitted us to conclude that, at least in the calcium fluoride columns, the contact angle of the n-alkane is not influenced by the capillary rise velocity, it taking in fact a null value during the process. On the other hand, it has been also proved that the driving force of the movement is caused by the replacement of the solid-vapour interface by the solid-liquid interface that happens during the imbibition, which means that only the Laplace's pressure, and not the precursor liquid film, contributes to the development of the phenomenon. Finally, it has been compared the values of the effective radius associated to each n-alkane, similar values being found independently from the particular liquid employed in the experiments, fact that indicates that the porous solid can be considered as a bunch of cylindrical and parallel capillaries of the same radius. 相似文献
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Y. Sun 《Physica D: Nonlinear Phenomena》2008,237(23):3089-3098
A novel two-phase diffuse-interface model is used to simulate flows inside a Hele-Shaw cell. The model assumes that the two phases coexist inside the diffuse interface, with different velocities and properties. A separate equation is used to calculate the slip velocity between the two phases inside the diffuse interface. It is shown that for one-dimensional flows parallel to the diffuse interface, the results are independent of the diffuse-interface width, regardless of the magnitude of the density and viscosity contrasts between the phases. This two-phase approach is coupled with a phase-field equation for calculating the interface motion. The model is applied to a buoyancy-driven two-phase flow involving a Rayleigh-Taylor instability and validated through a comparison with available sharp-interface results. The flows and interface topology changes are investigated for large density and viscosity contrasts between the phases. The convergence of the results with respect to the interface width is examined in detail. It is shown that the two-phase model converges better than a standard diffuse-interface model that assumes the presence of a single velocity inside the diffuse interface. Remaining interface width dependencies can be attributed to the capillary stress term in the momentum equation. 相似文献
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采用均质平衡流空泡模型,引入基于求解液体质量份数输运方程的空泡流模型,提出新的压力密度耦合的压缩性方法和控制气液两相转换的源项,求解汽水混合介质的RANS方程和带低雷诺数修正的k-ε模型,实现了小空化数(σ=0.2~0.01)下水下航行体的空泡流数值模拟.得到清晰的空泡形态特征与内部结构,以及空泡长度和最大直径随空化数的变化规律,给出航行体运动阻力系数与空化数之间的变化关系.将计算结果与解析结果及实验数据进行比较表明,该方法保证了极小空化数下自然空泡流计算的稳定性与收敛性,提高了空泡形态特性的预报精度. 相似文献
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建立了直流电场作用下协流式微流控装置中单乳液液滴乳化生成过程的非稳态理论模型,并开展了数值模拟研究,揭示了电场对液滴乳化生成动力学行为的调控机理,阐明了流场/电场参数对液滴乳化生成特性的影响规律.研究结果表明:沿流体流动方向施加静电场可在电物性参数不同的两相流体界面法线方向上产生指向内相流体的电场力,进而强化了内相流体界面的颈缩和断裂,提升了液滴生成速率和形变程度,减小了液滴生成尺寸;在同一毛细数下,随着电毛细数的增大,乳液乳化流型由每周期仅有单一液滴生成的滴式流型转变为每周期有一个主液滴并伴随有卫星液滴生成的滴式流型;随着毛细数和电毛细数的增大,黏性拖曳力以及电场力作用增强,使内相流体颈缩过程后期更容易形成细长型液线,从而有助于诱发液线上产生Rayleigh-Plateau不稳定现象,继而促进卫星液滴的形成. 相似文献