共查询到19条相似文献,搜索用时 15 毫秒
1.
Buoyant flow is analysed for a vertical fluid saturated porous layer bounded by an isothermal plane and an isoflux plane in
the case of a fully developed flow with a parallel velocity field. The effects of viscous dissipation and pressure work are
taken into account in the framework of the Oberbeck–Boussinesq approximation scheme and of the Darcy flow model. Momentum
and energy balances are combined in a dimensionless nonlinear ordinary differential equation solved numerically by a Runge–Kutta
method. Both cases of upward pressure force (upward driven flows) and of downward pressure force (downward driven flows) are examined. The thermal behaviour for upward driven flows and downward driven flows is quite different. For upward driven
flows, the combined effects of viscous dissipation and pressure work may produce a net cooling of the fluid even in the case
of a positive heat input from the isoflux wall. For downward driven flows, viscous dissipation and pressure work yield a net
heating of the fluid. A general reflection on the roles played by the effects of viscous dissipation and pressure work with
respect to the Oberbeck–Boussinesq approximation is proposed. 相似文献
2.
Combined, forced, and free flow in a vertical circular duct filled with a porous medium is investigated according to the Darcy–Boussinesq
model. The effect of viscous dissipation is taken into account. It is shown that a thermal boundary condition compatible with
fully developed and axisymmetric flow is either a linearly varying wall temperature in the axial direction or, only in the
case of uniform velocity profile, an axial linear-exponential wall temperature change. The case of a linearly varying wall
temperature corresponds to a uniform wall heat flux and includes the uniform wall temperature as a special case. A general
analytical solution procedure is performed, by expressing the seepage velocity profile as a power series with respect to the
radial coordinate. It is shown that, for a fixed thermal boundary condition, i.e., for a prescribed slope of the wall temperature,
and for a given flow rate, there exist two solutions of the governing balance equations provided that the flow rate is lower
than a maximum value. When the maximum value is reached, the dual solutions coincide. When the flow rate is higher than its
maximum, no axisymmetric solutions exist.
E. Magyari is on leave from the Institute of Building Technology, ETH—Zürich. 相似文献
3.
Oluropo Rufus Ayodele 《Transport in Porous Media》2006,64(2):171-184
Theoretical analysis is presented to quantify the viscous coupling effect in two-phase flow through porous media. The analysis
is based on the principle of potential difference equations as well as on the interfacial contact area and partition concept.
The analysis shows that viscous coupling effect is negligible throughout the normalized saturation range. The expression,
Xϕ 2, was developed for the quantification of the parameter that controls the amount of viscous coupling, where X was theoretically found to have a maximum value of 2. 相似文献
4.
Hydrodynamic instability in immiscible porous media flows in the presence of capillarity is investigated here. The analysis
and arguments presented here show that the slowdown of instabilities due to capillarity is usually very rapid which makes
the flow almost, but not entirely, stable. The profiles of the stable and unstable waves in the far-field are characterized
using a novel but very simple approach. 相似文献
5.
Viscous Fingering Instability in Porous Media: Effect of Anisotropic Velocity-Dependent Dispersion Tensor 总被引:1,自引:1,他引:0
The viscous fingering of miscible flow displacements in a homogeneous porous media is examined to determine the effects of
an anisotropic dispersion tensor on the development of the instability. In particular, the role of velocity-dependent transverse
and longitudinal dispersions is investigated through linear stability analysis and nonlinear simulations. It is found that
an isotropic velocity-dependent dispersion tensor does not affect substantially the development of the instability and effectively
has the same effect as molecular diffusion. On the other hand, an anisotropic velocity-dependent dispersion tensor results
in different instability characteristics and more intricate finger structures. It is shown that anisotropic dispersion has
profound effects on the development of the fingers and on the mechanisms of interactions between neighboring fingers. The
development of the new finger structures is explained by examining the velocity field and characterized qualitatively through
a spectral analysis of the average concentration and an analysis of the variations of the sweep efficiency and relative contact
area. 相似文献
6.
7.
Standard Galerkin finite element methods (GFEM) lack stability in solving advection-dominated solute transport in porous media.
They usually require prohibitively fine grids and extremely small time steps to solve for advection-dominated problems. The
algebraic subgrid-scale stabilized (ASGS) finite element method has been proved to overcome such problems for single-species
reactive transport. Its potential for dealing with multicomponent reactive transport has not yet been explored. Here we present
a numerical formulation of ASGS for steady and transient multicomponent reactive transport. Subgrid-scale transport equations
are solved first by using an ASGS approximation and their solutions are substituted back into the grid-scale equations. A
sequential iteration approach (SIA) is used to solve for coupled transport and chemical equations. Coupling of ASGS and SIA,
ASGS+SIA, has been implemented in a reactive transport code, CORE2D V4, and verified for conservative solute transport. ASGS+SIA has been tested for a wide range of 1-D transient multicomponent
reactive transport problems involving different types of chemical reactions such as: (1) Kinetically controlled aqueous species
degradation, (2) Kinetic mineral dissolution, (3) Serial-parallel decay networks, and (4) Cation exchange and pyrite oxidation
at local equilibrium. ASGS+SIA always provides accurate solutions and therefore offers an efficient option to solve for advection-dominated
multicomponent reactive transport problems. 相似文献
8.
When determining experimentally relative permeability and capillary pressure as a function of saturation, a self-consistent system of macroscopic equations, that includes Leverett's equation for capillary pressure, is required. In this technical note, such a system of equations, together with the conditions under which the equations apply, is formulated. With the aid of this system of equations, it is shown that, at the inlet boundary of a vertically oriented porous medium, static conditions pertain, and that potentials, because of the definition of potential, are equal in magnitude to pressures. Consequently, Leverett's equation is valid at the inlet boundary of the porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous. Moreover, it is demonstrated that Leverett's equation is valid for flow along the length of a vertically oriented porous medium, provided cocurrent flow, or gravity-driven, countercurrent flow is taking place, and provided the porous medium is homogeneous and there are no hydrodynamic effects. However, Leverett's equation is invalid for horizontal, steady-state, forced, countercurrent flow. When such flow is taking place, it is the sum of the pressures, and not the difference in pressures, which is related to capillary pressure. 相似文献
9.
The simultaneous flow of two phases through a three-dimensional porous medium is calculated by means of a Lattice-Boltzmann algorithm. The time-dependent phase configurations can be derived and also macroscopic quantities such as the relative permeabilities. When one phase only is supposed to be conductive, the Laplace equation which governs electrical conduction can be solved in each phase configuration; an instantaneous value of the macroscopic conductivity is obtained and it is averaged over many configurations. The influence of saturation on the resistivity index is studied for six different samples and two viscosity ratios. The saturation exponent is systematically determined. The numerical results are also compared to other possible models and also to experimental results; finally, they are discussed and criticized. 相似文献
10.
The viscous fingering instability of miscible reactive–dispersive flows in a homogeneous porous media is investigated through
nonlinear numerical simulations. In particular, the role of velocity-dependent transverse and longitudinal dispersions as
well as the type and rate of auto-catalytic chemical reactions is analyzed. It is found that for a third-order auto-catalytic
reaction, the higher the reaction rate, the more complex the finger structures. Furthermore, major differences between the
flow development of third-order and second-order autocatalytic reactions are reported. In addition, the anisotropy and velocity
dependence of the dispersion tensor are found to have a more profound effect on the fingering instability in the case of reactive
flows than in the non-reactive ones. The qualitative characterization of the finger structures is explained by examining the
flow velocity field and further quantified through an analysis of the average concentration and relative contact area. 相似文献
11.
A two-dimensional numerical model is used to study the nonlinear behavior of density gradients on transverse dispersion. Numerical
simulations are conducted using d
3
f, a computer code for simulation of density-dependent flow in porous media. Considering a density-stratified horizontal flow
in a heterogeneous porous media, a series of simulations is carried out to examine the effect of the density gradient on macro-scale
transverse dispersivity. Changing salt concentration significantly affects fluid properties. This physical behavior of the
fluid involves a non-linearity in modeling the interaction between salt and fresh water. It is concluded that the large-scale
transport properties for high density flow deviate significantly from the tracer case due to the spatial variation of permeability,
described by statistical parameters, at the local-scale. Indeed, the presence of vertical flow velocities induced by permeability
variations is responsible for the reduction of the mixing zone width in the steady state in the case of a high density gradient.
Uncertainties in the model simulations are studied in terms of discretization errors, boundary conditions, and convergence
of ensemble averaging. With respect to the results, the gravity number appears to be the controlling parameter for dispersive
flux. In addition, the applicability and limitations of the nonlinear model of Hassanizadeh (1990) and Hassanizadeh and Leijnse
(1995) (Adv Water Resour 18(4):203–215, 1995) in heterogeneous porous media are investigated. We found that the main cause
of the nonlinear behavior of dispersion, which is the interaction between density contrast and vertical velocity, needs to
be explicitly accounted for in a macro-scale model. 相似文献
12.
可压缩气体定常非Darcy渗流的流动分析及其应用 总被引:1,自引:0,他引:1
气体通过多孔介质的非Darcy流动具有广泛的工程应用背景,因此对多孔介质中的气体非Darcy流动进行流动分析有着非常重要的意义。然而,在通常的研究中,一般都将气体考虑为不可压缩流体,很少考虑气体的压缩性。对于高压气体以较高的速度通过多孔介质的情况,在进行流动分析时,不仅要考虑非Darcy效应,还必须考虑气体的压缩性。在本文中,对可压缩气体通过多孔介质的定常非Darcy流动进行了一维流动分析,得出了多孔介质中气体的压力分布和速度分布。还进一步给出了在高压差和高流速情况下,测定多孔介质材料渗透率和惯性系数的方法,以及多孔介质材料前后压力差与材料厚度的比Δp/L和材料有气流速度u1的解析关系。 相似文献
13.
We investigate a two-dimensional network simulator that models the dynamics of two-phase immiscible bulk flow where film flow can be neglected. We present a method for simulating the detailed dynamical process where the two phases are allowed to break up into bubbles, and bubbles are allowed to merge together. The notions of drainage and imbibition are not adequate to describe this process since there is no clear front between the fluids. In fact, the simulator is constructed so that one can study the behaviour of the system far from inlets and outlets, where the two fluids have been mixed together so much that all initial fronts have broken up. The simulator gives the fractional flow as a function of the saturation of each of the fluids. For the case of two fluids with equal viscosity, we classify flow regimes that are parametrized by the capillary number. 相似文献
14.
15.
This article presents the first instance of a double contact discontinuity in analytical solutions for multicomponent, two-phase
flow in porous media. We use a three-component system with constant equilibrium ratios and fixed injection and initial conditions,
to demonstrate this structure. This wave structure occurs for two-phase injection compositions. Such conditions were not considered
previously in the development of analytical solutions for compositional flows. We demonstrate the stability of the double
contact discontinuity in terms of the Liu entropy condition and also show that the resulting solution is continuously dependent
on initial data. Extensions to four-component and systems with adsorption are presented, demonstrating the more widespread
occurrence of this wave structure in multicomponent, two-phase flow systems. The developments in this article provide the
building blocks for the development of a complete Riemann solver for general initial and injection conditions. 相似文献
16.
关于渗流中流线不封闭的特性和条件 总被引:2,自引:0,他引:2
本文对于流体在多孔介质中流动的特性进行理论研究和数值计算,提出两个关于渗流中流线不封闭的特性和条件,得到了在一般工程实际情况中的多孔介质区域内部不存在封闭流线的结论。本文以突变截面圆管中不可压缩渗流为算例,利用半人工瞬变方法进行数值计算,得到流体在充满多孔介质的突扩截面圆管和突缩截面圆管中流动时关于速度分布和压力分布的结果。由此表明,在突变截面附近的渗流区域中不存在回流和分离流,也不存在封闭的流线。渗流的这些流动特性不同于在无多孔介质的空间区域中的流动特性。 相似文献
17.
18.
It is well known that the relationship between capillary pressure and saturation, in two-phase flow problems demonstrates memory effects and, in particular, hysteresis. Explicit representation of full hysteresis with a myriad of scanning curves in models of multiphase flow has been a difficult problem. A second complication relates to the fact that P
c–S relationships, determined under static conditions, are not necessarily valid in dynamics. There exist P
c–S relationships which take into account dynamic effects. But the combination of hysteretic and dynamic effects in the capillary relationship has not been considered yet. In this paper, we have developed new models of capillary hysteresis which also include dynamic effects. In doing so, thermodynamic considerations are employed to ensure the admissibility of the new relationships. The simplest model is constructed around main imbibition and drainage curves and assumes that all scanning curves are vertical lines. The dynamic effect is taken into account by introducing a damping coefficient in P
c–S equation. A second-order model of hysteresis with inclined scanning curves is also developed. The simplest version of proposed models is applied to two-phase incompressible flow and an example problem is solved. 相似文献
19.
Mathematical Model of Coalbed Gas Flow with Klinkenberg Effects in Multi-Physical Fields and its Analytic Solution 总被引:4,自引:0,他引:4
Guozhong Hu Hongtu Wang Xiaogang Fan Zhigang Yuan Song Hong 《Transport in Porous Media》2009,76(3):407-420
The deep-mining coal seam impacted by high in situ stress, where Klinkenberg effects for gas flow were very obvious due to
low gas permeability, could be regarded as a porous and tight gas-bearing media. Moreover, the Klinkenberg effects had a significant
effect on gas flow behavior of deep-mining coal seam. Based on the gas flow properties of deep-mining coal seams affected
by in situ stress field, geothermal temperature field and geo-electric field, a new mathematical model of coalbed gas flow,
which reflected the impact of Klinkenberg effects on coalbed gas flow properties in multi-physical fields, was developed by
establishing the flow equation, state equation, and continuity equation and content equation of coalbed gas. The analytic
solution was derived for the model of one-dimensional steady coalbed gas flow with Klinkenberg effects affected by in situ
stress field and geothermal temperature field, and a sensitivity analysis of its physical parameters was carried out by comparing
available analytic solutions and the measured values. The results show that the analytic solutions of this model of coalbed
gas flow with Klinkenberg effects are closer to the measured values compared to those without Klinkenberg effects, and this
model can reflect more accurately gas flow of deep-mining coal seams. Moreover, the analytic solution of this model is more
sensitive to the change of Klinkenberg factor b and temperature grad G than depth h. 相似文献