Preferential Flow Direction Research Articles

Tangential fluid flow within 3D narrow fissures: Conservative velocity fields on associated triangulations and transport processes

For a fissured medium with uncertainty in the knowledge of fractures' geometry, a conservative tangential flow field is constructed, which is consistent with the physics of stationary fluid flow in porous media and an interpolated geometry of the cracks. The flow field permits computing preferential fluid flow directions of the medium, rates of mechanical energy dissipations, and a stochastic matrix modeling stream lines and fluid mass transportation, for the analysis of solute/contaminant mass advection‐diffusion as well as drainage times.

Feasibility Study for The Setting Up of a Safety System for Monitoring CO2 Storage at Prinos Field, Greece

Geological storage of CO2 in subsurface geological structures can mitigate global warming. A comprehensive safety and monitoring system for CO2 storage has been undertaken for the Prinos hydrocarbon field, offshore northern Greece; a system which can prevent any possible leakage of CO2. This paper presents various monitoring strategies of CO2 subsurface movement in the Prinos reservoir, the results of a simulation of a CO2 leak through a well, an environmental risk assessment study related to the potential leakage of CO2 from the seafloor and an overall economic insight of the system. The results of the simulation of the CO2 leak have shown that CO2 reaches the seabed in the form of gas approximately 13.7 years, from the beginning of injection. From that point onwards the amount of CO2 reaching the seabed increases until it reaches a peak at around 32.9 years. During the injection period, the CO2 plume develops only within the reservoir. During the post-injection period, the CO2 reaches the seabed and develops side branches. These correspond to preferential lateral flow pathways of the CO2 and are more extensive for the dissolved CO2 than for the saturated CO2 gas. For the environmental risk assessment, we set up a model, using ArcGIS software, based on the use of data regarding the speeds of the winds and currents encountered in the region. We also made assumptions related to the flow rate of CO2. Results show that after a period of 10 days from the start of CO2 leakage the CO2 has reached halfway to the continental shores where the “Natura” protected areas are located. CO2 leakage modelling results show CO2 to be initially flowing along a preferential flow direction, which is towards the NE. However, 5 days after the start of leakage of CO2, the CO2 is also flowing towards the ENE. The consequences of a potential CO2 leak are considered spatially limited and the ecosystem is itself capable of recovering. We have tried to determine the costs necessary for the creation of such an integrated CO2 monitoring program both during the CO2 injection phase as well as during permanent storage. The most prevalent solution consists of purchasing both seismic equipment and Echosounder systems as well as privileging a monitoring system, which uses selected boreholes. The necessary period required for monitoring the study area is at least 20 years after the end of the CO2 storage period at Prinos. To the overall monitoring time, we should also add a further 20 years that are required for the injection phase as well as 12 years for the storage phase. The operating costs for monitoring the CO2 amount to 0,38 $/ton CO2 and the total cost for EOR at Prinos amounts to 0,45 $/ton CO2.

Physical and numerical modelling of shallow landslides

Physical modelling is an extremely useful tool for the study of the triggering process of shallow landslides. For this reason, in this work, numerous laboratory tests have been performed using a specific flume test apparatus. A wide range of initial soil conditions (i.e. porosity and water content) has been investigated to analyze the induced effect on failure time and mode, even simulating the presence of preferential flow directions within the soil. Different tests have been performed also reproducing, on a laboratory scale, the landslide event occurred on October 1, 2009, in the area where the testing material was sampled (i.e. Giampilieri, north-eastern Sicily, Italy). Furthermore, the experimental results have been employed to verify the capability of shallow landslide instability prediction (SLIP), a simplified stability model for the prediction of shallow landslide occurrence, to reproduce the triggering process.

The Piezoelectric Valve-Less Pump: Series and Parallel Connections

The piezoelectric valve-less pump is an attractive device to be used as a micropump for low flow rates. In these pumps, the nozzle/diffuser elements that have a preferential flow direction replace conventional valves, to direct the flow from the inlet to the outlet. This work is a study on the performance of such pumps when several of them (up to four) are combined for use in series and/or parallel arrangement. Two basic pumping configurations are considered: (a) pumping of fluid from low pressure to a higher pressure in an open circuit and (b) pumping of fluid in a closed circuit through a flow resistance. The performance analysis procedure developed is simple and quick and allows studying a wide range of operational conditions. Such an analysis is difficult to conduct using elaborate computational fluid dynamics (CFD) approach. The performance characteristics of the different combinations is reported and critically evaluated.

Stochastic generation of explicit pore structures by thresholding Gaussian random fields

We provide a description and computational investigation of an efficient method to stochastically generate realistic pore structures. Smolarkiewicz and Winter introduced this specific method in pores resolving simulation of Darcy flows (Smolarkiewicz and Winter, 2010 [1]) without giving a complete formal description or analysis of the method, or indicating how to control the parameterization of the ensemble. We address both issues in this paper. The method consists of two steps. First, a realization of a correlated Gaussian field, or topography, is produced by convolving a prescribed kernel with an initial field of independent, identically distributed random variables. The intrinsic length scales of the kernel determine the correlation structure of the topography. Next, a sample pore space is generated by applying a level threshold to the Gaussian field realization: points are assigned to the void phase or the solid phase depending on whether the topography over them is above or below the threshold. Hence, the topology and geometry of the pore space depend on the form of the kernel and the level threshold. Manipulating these two user prescribed quantities allows good control of pore space observables, in particular the Minkowski functionals. Extensions of the method to generate media with multiple pore structures and preferential flow directions are also discussed. To demonstrate its usefulness, the method is used to generate a pore space with physical and hydrological properties similar to a sample of Berea sandstone.

Dynamic properties of bright points in an active region

Context. Bright points (BPs) are small-scale, magnetic features ubiquitous across the solar surface. Previously, we have observed and noted their properties for quiet Sun regions. Here, we determine the dynamic properties of BPs using simultaneous quiet Sun and active region data. Methods. High spatial and temporal resolution G-band observations of active region AR11372 were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. Three subfields of varying polarity and magnetic flux density were selected with the aid of magnetograms obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Bright points within these subfields were subsequently tracked and analysed. Results. It is found that BPs within active regions display attenuated velocity distributions with an average horizontal velocity of ~0.6 km/s, compared to the quiet region which had an average velocity of 0.9 km/s. Active region BPs are also ~21% larger than quiet region BPs and have longer average lifetimes (~132s) than their quiet region counterparts (88 s). No preferential flow directions are observed within the active region subfields. The diffusion index (gamma) is estimated at ~1.2 for the three regions. Conclusions. We confirm that the dynamic properties of BPs arise predominately from convective motions. The presence of stronger field strengths within active regions is the likely reason behind the varying properties observed. We believe that larger amounts of magnetic flux will attenuate BP velocities by a combination of restricting motion within the intergranular lanes and by increasing the number of stagnation points produced by inhibited convection. Larger BPs are found in regions of higher magnetic flux density and we believe that lifetimes increase in active regions as the magnetic flux stabilises the BPs.

Induced polarization, resistivity, and self-potential: a case history of contamination evaluation due to landfill leakage

This article compares the efficiency of induced polarization (IP) and resistivity in characterizing a contamination plume due to landfill leakage in a typical tropical environment. The resistivity survey revealed denser electrical current flow that induced lower resistivity values due to the high ionic content. The increased ionic concentration diminished the distance of the ionic charges close to the membrane, causing a decrease in the IP phenomena. In addition, the self-potential (SP) method was used to characterize the preferential flow direction of the area. The SP method proved to be effective at determining the flow direction; it is also fast and economical. In this study, the resistivity results were better correlated with the presence of contamination (lower resistivity) than the IP (lower chargeability) data.

Kinetic responses of Dunaliella in moving fluids

The objective of this work was to quantify the kinetic behavior of Dunaliella primolecta (D. primolecta) subjected to controlled fluid flow under laboratory conditions. In situ velocities of D. primolecta were quantified by micron-resolution particle image velocimetry and particle tracking velocimetry. Experiments were performed under a range of velocity gradients and corresponding energy dissipation levels at microscopic scales similar to the energy dissipation levels of natural aquatic ecosystems. An average swimming velocity of D. primolecta in a stagnant fluid was 41 microm/s without a preferential flow direction. In a moving fluid, the sample population velocities of D. primolecta follow a log-normal distribution. The variability of sample population velocities was maximal at the highest fluid flow velocity in the channel. Local fluid velocity gradients inhibited the accrual of D. primolecta by twofold 5 days after the initiation of the experiment in comparison to the non-moving fluid control experiment.

Mechanics of fluid‐driven fracture growth in naturally fractured reservoirs with simple network geometries

A numerical model has been developed for fluid‐driven opening mode fracture growth in a naturally fractured formation. The rock formation contains discrete deformable fractures, which are initially closed but conductive because of their preexisting apertures. Fluid flow that develops along fractures depends on fracture geometry defined by preexisting aperture distribution, offsets along a fracture path, and intersections of two or more fractures. The model couples fluid flow, elastic deformation, and frictional sliding to obtain the solution, which depends on the competition between fractures for permeability enhancement. The fractures can be opened by fluid pressure that exceeds the normal stress acting on them and by interactions with intersecting closed fractures experiencing Coulomb‐type frictional slip. The Newtonian fluid is assumed to flow through the conductive fractures according to a lubrication equation that relates the cube of an equivalent hydraulic aperture to fracture conductivity. The rock material is assumed to be impermeable and elastic. This paper provides the governing equations for the multiple fracture systems and the solution methods used. Flow distribution and fracture growth in conductive fracture sets are simulated for a range of geometric arrangements and hydraulic properties. Numerical results show that elastic interaction between fracture branches plays a controlling role in fluid migration, although initial apertures can give rise to a preferential fluid flow direction during the early stage. In the presence of offsets, fracture segments subject to strong compression are difficult to open hydraulically, and their resulting smaller permeability can increase overall upstream fracture pressure and opening. The patterns of fluid flow become more complicated if fractures intersect each other. A portion of injected fluid is lost into closed empty fractures that cut across the main hydraulic fracture, and this delays the pressure increases required for fracture growth past the crosscutting fracture. The nonlinear fluid loss rate depends on the geometric complexities of the fracture sets and on the fluid viscosity. Sometimes fracture growth can be accelerated by the fast fluid transport along an intersected, relatively conductive natural fracture.

Spontaneous Break of Symmetry in Unconfined Laminar Annular Jets

Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow.

Evaluating parameter effects in a DEM ‘burning’ process based on land cover data

AbstractOver the last years, various methods regarding the use of digital land cover data to change digital elevation models (DEMs) have been reported in the literature. Usually, these methods rely on digital river networks (DRNs) or digital river and lake networks (DRLNs) to force preferential flow directions of pixels composing a DEM to get more realistic hydrological information, and reduce the accumulated number of errors in the information acquisition process. More recently, a new method that takes advantage of spatial distribution of rivers and floodplains derived from classified radar images has been presented. The method is based on a double ‘burning’ process. The first process uses stream lines to reduce elevations in the DEM (traditional stream burning approach—SB approach) and the second uses the floodplains to create valleys forcing the drainage of these areas to the main river. This approach, referred to as floodplain burning approach (FB approach), was applied to a basin in the Amazon basin. It greatly improved the results compared to the SB approach. However, this method requires the calibration of various parameters to represent accurately land cover types. This study proposes a comprehensive evaluation of the influence of these parameters on the DEM‐based hydrological information acquisition and on the original DEM. Consequently, a method of parameters set selection is provided. The method was applied to a sub‐basin of the Negro River basin in Amazonia. Several parameter combinations were evaluated in the watershed delineation process. Particular attention was paid to whether those parameters with a greater impact on DEM yielded better results in the case study. However, these DEM changes can be reduced with the knowledge of vegetation's heights, the vegetation having a substantial effect on remote acquisition of DEMs in tropical forests. Copyright © 2009 John Wiley & Sons, Ltd.

Integral formulation of shallow-water equations with anisotropic porosity for urban flood modeling

Summary An integral form of the shallow-water equations suitable for urban flood modeling is derived by applying Reynolds transport theorem to a finite control volume encompassing buildings on a flood plain. The effect of buildings on storage and conveyance is modeled with a binary density function i ( x , y ) that equals unity when ( x , y ) corresponds to a void, and nil otherwise, and can be measured using remote sensing data such as classified aerial imagery; the effect of buildings on flow resistance is modeled with a drag formulation. Discrete equations are obtained by applying the integral equations to a computational cell and adopting a Godunov-type, piecewise linear distribution of flow variables. The discrete equations include a volumetric porosity ϕ that represents the integral of i over the cell, normalized by the cell area, and an areal porosity ψ that represents the integral of i over an edge of the mesh, normalized by the edge length. The latter is directionally dependent which introduces anisotropy to the shallow-water equations and captures sub-grid preferential flow directions which occur in urban settings due to asymmetric building shapes and spacings and the alignment of buildings along streets. A important implication is that model predictions are necessarily grid dependent; therefore, a mesh design strategy is proposed. First- and second-order accurate numerical methods are presented to solve the discrete equations, and applications are shown for verification and validation purposes including the ability of the model to resolve preferential flow directions.

Borehole‐to‐borehole hydrologic response across 2.4 km in the upper oceanic crust: Implications for crustal‐scale properties

Subseafloor hydrologic observatories (CORKs) were installed in four boreholes in young seafloor on the eastern flank of the Juan de Fuca ridge to evaluate the hydrogeology of the upper oceanic crust. Two CORKs installed at Site 1301 were incompletely sealed, allowing cold bottom water to flow into basement at 2–5 L/s and causing a pressure perturbation in a preexisting sealed CORK at Site 1027, which was 2.4 km away. The pressure perturbation at Site 1027 is analyzed using conventional aquifer test methods, yielding transmissivity of T = 0.5 to 1.2 × 10−2 m2/s and bulk permeability of k = 0.7 to 2 × 10−12 m2 in the upper 300 m of basement. Storativity (a parameter that includes fluid and aquifer compressibilities, porosity, and layer thickness) is S = 1 to 3 × 10−3, corresponding to a crustal aquifer (matrix) compressibility of βm = 3 to 9 × 10−10 Pa−1. The inferred basement permeability is consistent with, but at the low end of, permeabilities calculated from single‐hole packer experiments at this and other young oceanic crustal sites; it is much less than values estimated from numerical models, analyses of formation response to tidal pressure oscillations, or pressure responses to coseismic strain events. The relatively low permeability indicated by the cross‐hole response may result from the basement aquifer in this area being azimuthally anisotropic, with a preferential flow direction oriented subparallel to the abyssal hill topography and tectonic structural fabric created at the ridge axis; this hypothesis will be tested during future experiments.

Two‐phase flow in structured packings: Modeling and calculation on a macroscopic scale

AbstractA model is presented that allows calculating the macroscopic flow field of counter‐current two‐phase flow in strongly anisotropic porous structures. It is applied to corrugated structured packings. All flow field variables and packing properties are averaged over the volume of an elementary cell. The anisotropic gas flow resistance is derived from measurements and from separate CFD calculations on 3D‐X‐ray CT scans. The liquid's flow resistance is calculated using an analytical model of liquid film flow on an inclined plate. Liquid flow along both preferential flow directions is represented by two separate phases, in order to consider horizontal forces despite their symmetry. Gas‐liquid momentum transfer above the loading point is included. The macroscopic flow field is calculated for a 288 mm I.D. column containing four packing elements. Liquid spreading from a point source, for uniform irrigation, increased hold‐up at the packing elements' joints and pressure drop are tested against experimental results. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Deep Air Sparging—15 to 46 m beneath the Water Table

AbstractAir sparging can be successfully applied to deep aquifers to remediate significant hydrocarbon mass in order to ultimately reach a point at which monitored natural attenuation can manage dissolved phase plumes. Air sparging is typically applied in shallow ground water conditions, less than 15 m beneath the water table (bwt). Deep air sparging, 15 to 46 m bwt, is more challenging but a viable alternative for treatment of residual petroleum hydrocarbons and dissolved phase constituents within a thick smear zone. An application to remediate an aquifer impacted by gasoline‐range petroleum hydrocarbons at depths greater than 76 m below ground surface (bgs) and up to 40 m thick (vertically) is reported here. Deep air sparging at 15, 31, and 46 m bwt was assessed using diagnostic tools involving flow rate, pressure, tracer gas, water table elevation, vapor concentration, and ground water chemistry measurements. The diagnostic tools identified preferential flow directions and a maximum depth of effective air injection. The full‐scale deep air sparging/soil vapor extraction (SVE) system removed more than 150,000 kg of hydrocarbon mass at the study site over a 3‐year period and ultimately greater than 100,000 kg/year with system expansion.

CFD Modelling and Calculation of Dynamic Two-Phase Flow in Columns Equipped with Structured Packing

Corrugated structured packings feature strong preferential flow directions due to their geometry of crossing triangular channels. This leads to good radial spreading, but causes stronger susceptibility to maldistribution of the phases. Detailed CFD calculations reflecting the exact packing structure are only feasible for very small sections of packing. However, effects like large scale maldistribution and instabilities in the flow field can only be modelled, if the hydrodynamics of the entire column are taken into account. In the present study, the macroscopic gas–liquid two-phase flow field of an entire column is modelled and numerically calculated. Both steady-state and dynamic cases are treated for counter-current operating conditions below the loading point. The model is based on the elementary cell model. It is extended to be used on anisotropic porous structures like corrugated structured packings. For the elementary cell model, flow field variables (velocity, phase volume fraction, pressure, and so on) and packing properties (void fraction, momentum exerted by the packing on the fluids, and so on) are averaged over the volume of one elementary cell. An elementary cell is the smallest periodically recurring structure of the porous material. For the gas phase, measurements of the pressure drop are conducted in different directions to model an anisotropic gas flow resistance tensor. The physically homogeneous liquid phase is split up for modelling purposes into two liquid phases, each of them representing film flow along one preferential flow direction. The numerical results are tested against X-ray radiographic measurements on a quasi two-dimensional segment of structured packing.

Cerebrospinal fluid flow in foramen magnum: temporal and spatial patterns at MR imaging in volunteers and in patients with Chiari I malformation.

To measure spatial and temporal variations in cerebrospinal fluid (CSF) flow through the cardiac cycle and throughout the subarachnoid space at magnetic resonance (MR) imaging in volunteer subjects with no known neurologic or spinal problems and in patients with Chiari I malformation. A cardiac-gated phase-contrast MR technique was used to acquire images at 14 time points evenly spaced through the cardiac cycle in 10 volunteers and eight patients with Chiari I malformation. Instantaneous CSF velocities were displayed as temporal and spatial plots and examined for homogeneity, differences between flow anterior and flow posterior to the spinal cord, synchronous bidirectional flow, and equivalence of the caudad flow and craniad flow in each voxel. Indexes for flow homogeneity, synchronous bidirectional flow, and preferential flow direction were calculated, and differences between the patient and volunteer groups were tested for significance with a t test of the means. In volunteers, diastolic velocity peaked in two regions in the anterior paramedial subarachnoid space. Patients had greater inhomogeneity of flow than volunteers. They had substantially increased flow (jets) in the anterior paramedial locations. Synchronous bidirectional flow was seen in six of the patients and in none of the volunteers. Cephalad flow in the jets or nodes (P =.05), proportion of cephalad and caudad flow in the anterior compartment (P <.005 for both), and the fraction of voxels with flow directionality (P =.03) differed significantly between patients and volunteers. CSF flow in symptomatic patients with Chiari I malformation, unlike that in volunteer subjects, is characterized by flow jets, regions with a preponderance of flow in one direction, and synchronous bidirectional flow.

3-D numerical simulations of flows in a cylindrical pleated filter packed with activated carbon cloth

This paper focuses on activated carbon cloths used for VOC treatment. The studied device is a cylindrical pleated filter that is developed for the implementation of these materials in dynamic systems. 3-D numerical simulations of flows have been performed to determine the flow structure in this kind of geometry. The analysis of the flow structure reveals preferential flow directions in the pleated medium. The local velocity range near the fabric could be 10 times higher than the average velocity calculated for the whole developed surface of the filter, but even the maximal value of the velocity (0.3 m s −1) is acceptable for adsorption. Overlap phenomena are revealed and dead zones estimated. The influence of the number of pleats in such a device on the aerodynamic performance is also studied.

The piezoelectric valve-less pump - improved dynamic model

The piezoelectric valve-less pump is an attractive device to be used as a micro pump for low flow rates. The pump converts the reciprocating motion of a diaphragm, activated by a piezoelectric disk, into a pumping action. Instead of conventional valves, which have moving parts, nozzle/diffuser elements that have a preferential flow direction are used to direct the flow from the inlet to the outlet. In this paper, an improved dynamic model for the simulation of valve-less piezoelectric pumps is presented. The model is capable of accurate simulation of the pump performance including the natural frequency, flow rate, and pressure drop. The model is utilized here to study the effect of the driving frequency and the inlet/outlet length and diameter of the leading pipes on the pump performance. Comparison with experiments shows good agreement with a minimal number of adjusting parameters.

Mise en évidence par résistivité électrique des écoulements préférentiels et de l'assèchement par le maı̈s d'un CALCISOL de Beauce irrigué

Soil electrical resistivity decreases with water saturation. During irrigation of a soil of Beauce with a corn crop cover, a non-destructive multi-electrode 2D electrical method, spatially integrative, was tested jointly with TDR measurements (Time Domain of Reflectometry) of water content to realise a study of soil water flow with time. The results presented show that the method employed is well suited to the question investigated. The soil volumes dried up by corn roots, the wetting front movement and the preferential flow directions were identified and located. La résistivité électrique d'un sol diminue avec sa saturation en eau. Lors de l'irrigation d'un sol de Beauce cultivé en maı̈s, une méthode électrique 2D multiélectrode, non destructive et spatialement intégrante, a été testée, conjointement à des mesures TDR ( Time Domain Reflectometry ) de la teneur en eau, pour réaliser un suivi temporel des flux hydriques dans le sol. Les résultats montrent que la méthode employée est adaptée. Les volumes desséchés par les prélèvements racinaires, la progression du front d'infiltration et les zones d'écoulements préférentiels sont identifiés et localisés.