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Hongbin Zhan - One of the best experts on this subject based on the ideXlab platform.

  • reactive solute transport in an asymmetrical Fracture rock matrix system
    Advances in Water Resources, 2018
    Co-Authors: Renjie Zhou, Hongbin Zhan
    Abstract:

    Abstract The understanding of reactive solute transport in a Single Fracture–rock matrix system is the foundation of studying transport behavior in the complex Fractured porous media. When transport properties are asymmetrically distributed in the adjacent rock matrixes, reactive solute transport has to be considered as a coupled three-domain problem, which is more complex than the symmetric case with identical transport properties in the adjacent rock matrixes. This study deals with the transport problem in a Single Fracture–rock matrix system with asymmetrical distribution of transport properties in the rock matrixes. Mathematical models are developed for such a problem under the first-type and the third-type boundary conditions to analyze the spatio–temporal concentration and mass distribution in the Fracture and rock matrix with the help of Laplace transform technique and de Hoog numerical inverse Laplace algorithm. The newly acquired solutions are then tested extensively against previous analytical and numerical solutions and are proven to be robust and accurate. Furthermore, a water flushing phase is imposed on the left boundary of system after a certain time. The diffusive mass exchange along the Fracture/rock matrixes interfaces and the relative masses stored in each of three domains (Fracture, upper rock matrix, and lower rock matrix) after the water flushing provide great insights of transport with asymmetric distribution of transport properties. This study has the following findings: 1) Asymmetric distribution of transport properties imposes greater controls on solute transport in the rock matrixes. However, transport in the Fracture is mildly influenced. 2) The mass stored in the Fracture responses quickly to water flushing, while the mass stored in the rock matrix is much less sensitive to the water flushing. 3) The diffusive mass exchange during the water flushing phase has similar patterns under symmetric and asymmetric cases. 4) The characteristic distance which refers to the zero diffusion between the Fracture and the rock matrix during the water flushing phase is closely associated with dispersive process in the Fracture.

  • reactive solute transport in a filled Single Fracture matrix system under unilateral and radial flows
    Advances in Water Resources, 2017
    Co-Authors: Renjie Zhou, Hongbin Zhan, Kewei Chen
    Abstract:

    Abstract The study of transport processes in a Single Fracture is the basis of understanding transport in complex Fractured networks. Many Single Fractures in the field are filled with sediments, and the transport in such filled Single Fractures has received much less attention up to present. When the Fracture is partially filled with sediments, a mobile-immobile approach is considered necessary. This study deals with a coupled three-domain transport problem using mobile and immobile domains to characterize a filled Single Fracture and a matrix domain to characterize the rock body. Mathematical models are developed for such a coupled three-domain transport problem with new semi-analytical solutions to analyze the spatial-temporal concentration and mass distributions in the Fracture and rock matrix with the help of Laplace transforms. This study addresses transport in a filled Fracture-matrix system under two different flow conditions: unilateral flow, and radial flow. The new solutions have been tested extensively against previous solutions under various special settings and are proven to be robust and accurate. This study has the following findings: 1) Longitudinal dispersion in the Fracture often plays an important role in such a coupled system in unilateral flow, 2) Mass partitions in three domains follow similar patterns in respect to the influence of Fracture apertures, mobile/immobile ratios, and first-order mass transfer rates, 3) The system is most sensitive to the dispersivity and least sensitive to the first-order mass transfer rate and the mobile/immobile ratio in the unilateral flow model over a wide range of time scales (if the longitudinal dispersivity and Darcian flow velocity remain constant), 4) The system is most sensitive to the dispersivity, less sensitive to the mobile/immobile ratio, and least sensitive to the first-order mass transfer rate in the radial flow model (if the radial dispersivity and injection rate remain constant).

  • the effect of expansion ratio on the critical reynolds number in Single Fracture flow with sudden expansion
    Hydrological Processes, 2016
    Co-Authors: Jiazhong Qian, Hongbin Zhan, Xiao Wang, Mu Wang
    Abstract:

    Flow in a Single Fracture (SF) is an important research subject in groundwater hydrology, hydraulic engineering, radioactive nuclear waste repository and geotechnical engineering. An abruptly changing aperture is a unique type of SF. This study discusses the relation between the values of the critical Reynolds number (Rec) for the onset of symmetry breaking of flow and the expansion ratio (E) of SF, which is defined as the ratio between the outlet (D) and inlet (d) apertures. This study also investigates the effect of inlet aperture d on Rec for flow in an SF with abruptly changing apertures (SF-ACA) using the finite volume method. Earlier numerical and experimental results showed that flow is symmetric in respect to the central plane of the SF-ACA at small Reynolds number (Re) but becomes asymmetric when Re is sufficiently large. Our simulations show that the value of Rec decreases with the increasing E, and the relationship between the logarithm of Rec and E can be described accurately using either a quadratic polynomial function or a logarithmic function. However, the relationship of Rec and d for a given E value is vague, and Rec becomes even less sensitive to d when E increases. This study also reveals that the hydraulic gradient (J) and flow velocity (v) follow a super-linear relationship that can be fitted almost perfectly by the Forchheimer equation. The inertial component (Ji) of J increases monotonically with Re, whereas the viscous component (Jv) of J decreases monotonically with Re. The Re value corresponding to equal inertial and viscous components of J (named as the transitional point Re) decreases when E increases, and such a transitional point Re should be closely related to the critical Reynolds number Rec, although a rigorous theoretical proof is not yet available. Copyright © 2015 John Wiley & Sons, Ltd.

  • eddy correlations for water flow in a Single Fracture with abruptly changing aperture
    Hydrological Processes, 2012
    Co-Authors: Jiazhong Qian, Hongbin Zhan, Min Liang, Zhou Chen
    Abstract:

    Fluid flow in Single Fractures with non-uniform apertures is an important research subject in many disciplines. The abruptly changing aperture is a special case of such non-uniformity. This paper simulates water flow in a Single Fracture with abruptly changing aperture (SF-ACA) using the Lattice Boltzmann Method (LBM) and the Finite Volume Method (FVM). The flow occurs with the Reynolds number (Re) ranging from 5 to 900 and a ratio of aperture change (E) of 3 (E = D/d, where D and d are the larger and smaller apertures, respectively). For Re values between 5 and 100, both LBM and FVM can successfully simulate the eddy development in the expansion regime of an SF-ACA. Flow with high Re values (up to 900) is simulated by FVM, which appears to be numerically more stable than LBM for high-Re flow problems studied here. The flow symmetry in the expansion regime breaks at the Re value between 400 and 500. Our simulation result shows a linear relationship between l1/d and Re at low Re (5–100) or higher Re (110–900) values, where defined as the length from the location of abrupt expansion to the right edge of the first eddy along the flow direction. If considering the simulation results for the entire simulated range of Re (5–900), the l1/d–Re relationship is better described by a non-linear logarithmical function. The l1/d approaches an asymptotic constant at large Re. Copyright © 2011 John Wiley & Sons, Ltd.

B Wang - One of the best experts on this subject based on the ideXlab platform.

  • simulation of two phase flow in horizontal Fracture networks with numerical manifold method
    Advances in Water Resources, 2017
    Co-Authors: L F Fan, H D Wang, B Wang
    Abstract:

    Abstract The paper presents simulation of two-phase flow in discrete Fracture networks with numerical manifold method (NMM). Each phase of fluids is considered to be confined within the assumed discrete interfaces in the present method. The homogeneous model is modified to approach the mixed fluids. A new mathematical cover formation for Fracture intersection is proposed to satisfy the mass conservation. NMM simulations of two-phase flow in a Single Fracture, intersection, and Fracture network are illustrated graphically and validated by the analytical method or the finite element method. Results show that the motion status of discrete interface significantly depends on the ratio of mobility of two fluids rather than the value of the mobility. The variation of fluid velocity in each Fracture segment and the driven fluid content are also influenced by the ratio of mobility. The advantages of NMM in the simulation of two-phase flow in a Fracture network are demonstrated in the present study, which can be further developed for practical engineering applications.

  • simulation of two phase flow in horizontal Fracture networks with numerical manifold method
    Advances in Water Resources, 2017
    Co-Authors: H D Wang, B Wang
    Abstract:

    Abstract The paper presents simulation of two-phase flow in discrete Fracture networks with numerical manifold method (NMM). Each phase of fluids is considered to be confined within the assumed discrete interfaces in the present method. The homogeneous model is modified to approach the mixed fluids. A new mathematical cover formation for Fracture intersection is proposed to satisfy the mass conservation. NMM simulations of two-phase flow in a Single Fracture, intersection, and Fracture network are illustrated graphically and validated by the analytical method or the finite element method. Results show that the motion status of discrete interface significantly depends on the ratio of mobility of two fluids rather than the value of the mobility. The variation of fluid velocity in each Fracture segment and the driven fluid content are also influenced by the ratio of mobility. The advantages of NMM in the simulation of two-phase flow in a Fracture network are demonstrated in the present study, which can be further developed for practical engineering applications.

Suresh G Kumar - One of the best experts on this subject based on the ideXlab platform.

  • time dependent dispersivity of linearly sorbing solutes in a Single Fracture with matrix diffusion
    Journal of Hydrologic Engineering, 2008
    Co-Authors: Muddu Sekhar, Suresh G Kumar, Debasmita Misra
    Abstract:

    Field studies show that the variance of travel distance often increases nonlinearly with time elapsed after release of solute tracers. The nonlinear relationship between variance of travel distance and time is attributed to the heterogeneity of the porous media. To describe the transport in such a heterogeneous system, a time-dependent dispersivity is necessary. Though more attention has been devoted toward the study of non-Fickian dispersion at early time, there are no known studies that explicitly describe the dispersivity behavior in a Fracture–matrix-coupled system. The observation from numerical results suggests that dispersivity has a time-dependent behavior and it reaches asymptotic values after a long time. The preasymptotic behavior of a solute front in Fracture is characterized by increasing effective dispersivity with time. The role of Fracture and matrix transport parameters on this behavior is analyzed for linearly sorbing solutes. Approximate expression is provided for the time-dependent dispersivity of the solute front in a Single Fracture with matrix diffusion and the expression for the time required to attain the asymptotic behavior is also obtained. A comparison of the front dispersivity behavior between parallel multiple Fractures with a constant aperture width model and smooth parallel multiple Fractures with a varying aperture width model is done.

  • effect of sorption intensities on dispersivity and macro dispersion coefficient in a Single Fracture with matrix diffusion
    Hydrogeology Journal, 2008
    Co-Authors: Suresh G Kumar
    Abstract:

    Matrix diffusion and sorption are among the key processes impacting the efficiency of natural attenuation in the subsurface. While these processes have been studied extensively in Fractured media, limited information exists on the sorption nonlinearity. To address this shortfall, a numerical model has been developed that couples matrix diffusion and nonlinear sorption at the scale of a Single Fracture using the dual-porosity concept. The study is limited to a constant continuous-solute-source boundary condition. The influence of sorption intensities on dispersivity and macro-dispersion coefficient is investigated using a method of spatial moments. Results suggest that mixing of solutes is significantly lowered by nonlinear sorptive behavior, with respect to the mixing caused by matrix diffusion for linearly sorbing solutes. Also, the magnitude of time dependent dispersivity during the pre-asymptotic regime is lower for nonlinearly sorbing solutes with respect to the linearly sorbing solutes. Reduced mixing is also observed for nonlinearly sorbing solutes under combined mechanisms of matrix diffusion and decay.

  • spatial moment analysis for one dimensional nonisothermal quartz transport and dissolution precipitation in Fracture matrix system
    Journal of Hydrologic Engineering, 2006
    Co-Authors: Suresh G Kumar, Ahmad Ghassemi
    Abstract:

    This paper presents a spatial-moment analysis of nonisothermal solute transport with simplified dissolution/precipitation of quartz in a Single Fracture-matrix system using a dual porosity framework. For this purpose, a one-dimensional coupled thermal and solute transport between an injection and a production well is modeled numerically to obtain spatial distribution of temperature and concentration profiles along the Fracture. Subsequently, concentration based on first and second spatial moments is evaluated. The effective macrodispersion coefficient is analyzed to study its influence on water velocity, Fracture aperture, reservoir diffusion coefficient, reservoir thermal conductivity, reservoir porosity, quartz fraction of the reservoir, and the initial reservoir temperature. The results suggest a non-Fickian behavior that approaches a Fickian behavior due to the effect of coupled matrix diffusion. The mixing characteristics near the injection well are highly sensitive to the above-mentioned parameters at early times, but this mixing effect is subsequently suppressed away from the injection well.

  • spatial moment analysis for transport of nonreactive solutes in Fracture matrix system
    Journal of Hydrologic Engineering, 2005
    Co-Authors: Suresh G Kumar, M Sekhar
    Abstract:

    This paper presents an analysis using spatial moments for transport of nonreactive solutes in a Single Fracture-matrix system using a dual porosity framework. The velocity and dispersion obtained using the first and second spatial moments are found to have two regimes. The effect of Fracture velocity, Fracture dispersivity, Fracture spacing, matrix diffusion coefficient, and matrix porosity on both regimes are analyzed. The first regime is characterized by a behavior wherein both velocity and dispersion are functions of time and all of the above parameters of the Fracture-matrix system are found to have an influence. In the second regime, they are independent of time similar to the behavior of conservative solutes in an ideal porous media. This regime is characterized by the influence of a few parameters of the Fracture-matrix system. The empirical relationships for solute velocity, macrodispersion coefficient, and dispersivity in the asymptotic stage are presented.

H D Wang - One of the best experts on this subject based on the ideXlab platform.

  • simulation of two phase flow in horizontal Fracture networks with numerical manifold method
    Advances in Water Resources, 2017
    Co-Authors: L F Fan, H D Wang, B Wang
    Abstract:

    Abstract The paper presents simulation of two-phase flow in discrete Fracture networks with numerical manifold method (NMM). Each phase of fluids is considered to be confined within the assumed discrete interfaces in the present method. The homogeneous model is modified to approach the mixed fluids. A new mathematical cover formation for Fracture intersection is proposed to satisfy the mass conservation. NMM simulations of two-phase flow in a Single Fracture, intersection, and Fracture network are illustrated graphically and validated by the analytical method or the finite element method. Results show that the motion status of discrete interface significantly depends on the ratio of mobility of two fluids rather than the value of the mobility. The variation of fluid velocity in each Fracture segment and the driven fluid content are also influenced by the ratio of mobility. The advantages of NMM in the simulation of two-phase flow in a Fracture network are demonstrated in the present study, which can be further developed for practical engineering applications.

  • simulation of two phase flow in horizontal Fracture networks with numerical manifold method
    Advances in Water Resources, 2017
    Co-Authors: H D Wang, B Wang
    Abstract:

    Abstract The paper presents simulation of two-phase flow in discrete Fracture networks with numerical manifold method (NMM). Each phase of fluids is considered to be confined within the assumed discrete interfaces in the present method. The homogeneous model is modified to approach the mixed fluids. A new mathematical cover formation for Fracture intersection is proposed to satisfy the mass conservation. NMM simulations of two-phase flow in a Single Fracture, intersection, and Fracture network are illustrated graphically and validated by the analytical method or the finite element method. Results show that the motion status of discrete interface significantly depends on the ratio of mobility of two fluids rather than the value of the mobility. The variation of fluid velocity in each Fracture segment and the driven fluid content are also influenced by the ratio of mobility. The advantages of NMM in the simulation of two-phase flow in a Fracture network are demonstrated in the present study, which can be further developed for practical engineering applications.

Luis Moreno - One of the best experts on this subject based on the ideXlab platform.

  • solute transport along a Single Fracture with a finite extent of matrix a new simple solution and temporal moment analysis
    Journal of Hydrology, 2018
    Co-Authors: Shuo Meng, Ivars Neretnieks, Longcheng Liu, Batoul Mahmoudzadeh, Luis Moreno
    Abstract:

    Abstract A new simple and robust solution, based on uniform steady-state flow velocity, is developed for the problem of solute transport in a Fracture-matrix system with a finite penetration depth of a radioactive contaminant into the rock matrix. The solution is an extension of Liu et al. (2017) to finite penetration depth and an alternative solution strategy to the problem solved by Sudicky et al. (1982). The solution takes the form of a convolution of two functions. The first function describes the probability density function of the residence time distribution of a conservative solute resulting merely from advection and Fickian dispersion. The second function is actually the impulse response of the Fracture-matrix system in the case of a plug flow without any hydrodynamic dispersion. As a result, the effects of Fickian dispersion and matrix diffusion on solute transport are decoupled, and thus the resulting breakthrough curve can be analyzed in terms of those two functions. In addition to this, the derived Peclet numbers of those two functions, based on temporal moments, are also found to be associated with the derived Peclet number of the resulting breakthrough curve. By comparing the Peclet numbers of those two functions, the contribution of Fickian dispersion and matrix diffusion to solute spreading is determined in a straightforward way. This can aid to find out the dominating mechanism on solute transport, and therefore the performance of breakthrough curve can be approximated by only one function in some specific cases.

  • solute transport along a Single Fracture in a porous rock a simple analytical solution and its extension for modeling velocity dispersion
    Hydrogeology Journal, 2018
    Co-Authors: Longcheng Liu, Ivars Neretnieks, Pirouz Shahkarami, Shuo Meng, Luis Moreno
    Abstract:

    A simple and robust solution is developed for the problem of solute transport along a Single Fracture in a porous rock. The solution is referred to as the solution to the Single-flow-path model and takes the form of a convolution of two functions. The first function is the probability density function of residence-time distribution of a conservative solute in the Fracture-only system as if the rock matrix is impermeable. The second function is the response of the Fracture-matrix system to the input source when Fickian-type dispersion is completely neglected; thus, the effects of Fickian-type dispersion and matrix diffusion have been decoupled. It is also found that the solution can be understood in a way in line with the concept of velocity dispersion in Fractured rocks. The solution is therefore extended into more general cases to also account for velocity variation between the channels. This leads to a development of the multi-channel model followed by detailed statistical descriptions of channel properties and sensitivity analysis of the model upon changes in the model key parameters. The simulation results obtained by the multi-channel model in this study fairly well agree with what is often observed in field experiments—i.e. the unchanged Peclet number with distance, which cannot be predicted by the classical advection-dispersion equation. In light of the findings from the aforementioned analysis, it is suggested that forced-gradient experiments can result in considerably different estimates of dispersivity compared to what can be found in natural-gradient systems for typical channel widths.