› › Numerical Investigation Of Field Scale Convective Mixing Processes In Heterogeneous Variable Density Flow Systems Using High Resolution Adaptive Mesh Refinement Methods

Numerical Investigation of Field-scale Convective Mixing Processes in Heterogeneous, Variable-density Flow Systems Using High-resolution Adaptive Mesh Refinement Methods

Author : Douglas Jay Cosler

Publisher :

Page : 180 pages

File Size : 42,43 MB

Release : 2006

Category : Aquifer storage recovery

ISBN :

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Abstract: Three-dimensional, field-scale (~ 100 m) convective mixing processes in heterogeneous porous media are examined. The focus is on fluid mixing rates and density-dependent macrodispersion, and the influence of small-scale (~ centimeters) instability development on large-scale variable-density flow and solute transport behavior. Dynamic adaptive mesh refinement methods (AMR) and a higher-order (solute advection term), mass-conservative Eulerian-Lagrangian discretization scheme for the solute transport equation are used to construct a new numerical code (DensTransAMR) that automatically adjusts to multiple scales of convective mixing processes by translating and adding/removing telescoping levels of progressively finer subgrids during a simulation. Because the flow and transport solutions for each subgrid are computed independently, field-scale simulations are broken into multiple smaller problems that can be modeled more efficiently and with finer detail. Two types of numerical experiments are performed: freshwater injection in a saltwater aquifer and dense fluid injection in a freshwater aquifer. Convective mixing rates are related to the geostatistical properties of the aquifer (variance and mean of the log permeability distribution, horizontal and vertical correlation scales), the fluid density difference, the magnitude of local small-scale dispersion, the effects of different permeability field realizations, the injection well size and orientation, hydraulic parameters such as injection rate and regional hydraulic gradient, and the spatial resolution. Convective mixing in heterogeneous porous media is shown to be more amenable to prediction than previously concluded. Computed three-dimensional fluid mixing rates are related to mathematical expressions for density-dependent macrodispersivity that are based on stochastic flow and solute transport theory and are a function of log permeability variance, the correlation scale, and a time-dependent parameter. Different instability patterns are generated when a different permeability field realization is used, the source location changes, or the mesh spacing is varied. However, long-term fluid mixing rates (i.e., after the mixing zone becomes large compared with the correlation scale) do not change if the fluid and macroscopic porous media properties (mean permeability, variance, and correlation lengths) remain constant. Porous media variability on scales smaller than the correlation lengths has an effect on the fluid mixing zone volume but does not affect long-term mixing rates.





Adaptive Mesh Refinement - Theory and Applications

Author : Tomasz Plewa

Publisher : Springer Science & Business Media

Page : 550 pages

File Size : 30,94 MB

Release : 2005-12-20

Category : Mathematics

ISBN : 3540270396

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Advanced numerical simulations that use adaptive mesh refinement (AMR) methods have now become routine in engineering and science. Originally developed for computational fluid dynamics applications these methods have propagated to fields as diverse as astrophysics, climate modeling, combustion, biophysics and many others. The underlying physical models and equations used in these disciplines are rather different, yet algorithmic and implementation issues facing practitioners are often remarkably similar. Unfortunately, there has been little effort to review the advances and outstanding issues of adaptive mesh refinement methods across such a variety of fields. This book attempts to bridge this gap. The book presents a collection of papers by experts in the field of AMR who analyze past advances in the field and evaluate the current state of adaptive mesh refinement methods in scientific computing.



Mesh Adaption Strategies for Vortex-dominated Flows

Author : Sean Javad Kamkar

Publisher : Stanford University

Page : 218 pages

File Size : 47,41 MB

Release : 2011

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ISBN :

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A new adaptive mesh refinement strategy that is based on a coupled feature-detection and error-estimation approach is developed. The overall goal is to apply the proper degree of refinement to key vortical features in aircraft and rotorcraft wakes. The refinement paradigm is based on a two-stage process wherein the vortical regions are initially identified for refinement using feature-detection, and then the appropriate resolution is determined by the local solution error. The feature-detection scheme uses a local normalization procedure that allows it to automatically identify regions for refinement with threshold values that are not dependent upon the convective scales of the problem. An error estimator, based on the Richardson Extrapolation method, then supplies the identified features with appropriate levels of refinement. The estimator is shown to be well-behaved for steady-state and time-accurate aerodynamic flows. The above strategy is implemented within the Helios code, which features a dual-mesh paradigm of unstructured grids in the near-body domain, and adaptive Cartesian grids in the off-body domain. A main objective of this work is to control the adaption process so that high fidelity wake resolution is obtained in the off-body domain. The approach is tested on several theoretical and practical vortex-dominated flow-fields in an attempt to resolve wingtip vortices and rotor wakes. Accuracy improvements to rotorcraft performance metrics and increased wake resolution are simultaneously documented.



Adaptive Mesh Refinement Method for CFD Applications

Author : Oscar Luis Antepara Zambrano

Publisher :

Page : 158 pages

File Size : 17,35 MB

Release : 2019

Category :

ISBN :

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The main objective of this thesis is the development of an adaptive mesh refinement (AMR) algorithm for computational fluid dynamics simulations using hexahedral and tetrahedral meshes. This numerical methodology is applied in the context of large-eddy simulations (LES) of turbulent flows and direct numerical simulations (DNS) of interfacial flows, to bring new numerical research and physical insight. For the fluid dynamics simulations, the governing equations, the spatial discretization on unstructured grids and the numerical schemes for solving Navier-Stokes equations are presented. The equations follow a discretization by conservative finite-volume on collocated meshes. For the turbulent flows formulation, the spatial discretization preserves symmetry properties of the continuous differential operators and the time integration follows a self-adaptive strategy, which has been well tested on unstructured grids. Moreover, LES model consisting of a wall adapting local-eddy-viscosity within a variational multi-scale formulation is used for the applications showed in this thesis. For the two-phase flow formulation, a conservative level-set method is applied for capturing the interface between two fluids and is implemented with a variable density projection scheme to simulate incompressible two-phase flows on unstructured meshes. The AMR algorithm developed in this thesis is based on a quad/octree data structure and keeps a relation of 1:2 between levels of refinement. In the case of tetrahedral meshes, a geometrical criterion is followed to keep the quality metric of the mesh on a reasonable basis. The parallelization strategy consists mainly in the creation of mesh elements in each sub-domain and establishes a unique global identification number, to avoid duplicate elements. Load balance is assured at each AMR iteration to keep the parallel performance of the CFD code. Moreover, a mesh multiplication algorithm (02) is reported to create large meshes, with different kind of mesh elements, but preserving the topology from a coarser original mesh. This thesis focuses on the study of turbulent flows and two-phase flows using an AMR framework. The cases studied for LES of turbulent flows applications are the flow around one and two separated square cylinders, and the flow around a simplified car model. In this context, a physics-based refinement criterion is developed, consisting of the residual velocity calculated from a multi-scale decomposition of the instantaneous velocity. This criteria ensures grid adaptation following the main vortical structures and giving enough mesh resolution on the zones of interest, i.e., flow separation, turbulent wakes, and vortex shedding. The cases studied for the two-phase flows are the DNS of 2D and 3D gravity-driven bubble, with a particular focus on the wobbling regime. A study of rising bubbles in the wobbling regime and the effect of dimensionless numbers on the dynamic behavior of the bubbles are presented. Moreover, the use of tetrahedral AMR is applied for the numerical simulation of gravity-driven bubbles in complex domains. On this topic, the methodology is validated on bubbles rising in cylindrical channels with different topology, where the study of these cases contributed to having new numerical research and physical insight in the development of a rising bubble with wall effects.



Adaptive Mesh Refinement for Finite Element Flow Modeling in Complex Geometries

Author : Sujata Prakash

Publisher :

Page : 0 pages

File Size : 13,61 MB

Release : 1999

Category :

ISBN :

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Adaptive mesh refinement is a powerful tool for obtaining the highest solution accuracy for a given computational effort. Over the past decade, many adaptive techniques have been developed and applied to a variety of fluid flow problems. Results obtained for compressible flows, and to an extent, 2D incompressible flows have been impressive, however, similar progress has not been noted for 3D incompressible flows, particularly in complicated geometries. The objective of this thesis was to develop and test an adaptive solution methodology for 3D incompressible flow simulations in domains of arbitrary complexity. To characterize the finite element solution error, the Zienkiewicz-Zhu patch recovery error estimator (LPR) was adopted. An enhanced version of the LPR error estimator was formulated and implemented using 10-noded tetrahedral elements. The enhanced estimator (LPRC) resulted in significantly improved gradient recovery (and consequently, improved error estimates) at virtually no additional computational cost. For mesh refinement, an elemental subdivision procedure was implemented. To enable refinement in complex geometries, a procedure for preserving the boundary integrity of a refined mesh was developed. This methodology can be used for geometric data from any solid modeling (CAD) system provided the data can be exported in the IGES format. A benchmark study of the AMR procedure, in which steady flow over a three-dimensional backward-facing step was simulated, showed that the cumulative computational effort required in the adaptive analysis was lower than that required in a non-adaptive analysis of the same problem. In the second phase of this work, the AMR procedure was applied to modeling flow through two arterial geometries. Specifically, flows in an idealized end-to-side anastomosis and in a human right coronary artery were examined. Both studies assessed whether an AMR analysis could achieve more accurate solutions than conventional analyses that utilize high-resolution meshes whose gradation is based on 'a priori' knowledge of the flow field. It was noted that mesh-independent velocity fields were not very difficult to obtain even in the absence of an adaptive methodology. However, wall shear stress fields were much more difficult to absolutely resolve non-adaptively. Given that shear stresses occurring on arterial walls are widely believed to be a key factor governing the development of arterial disease, it is very important to accurately resolve wall shear stress fields if confidence can be placed in the results of numerical simulations of arterial flow phenomena. These results indicate that wall shear stress is an extremely sensitive measure of spatial resolution, and that the systematic solution-adaptive methodology developed in this thesis is very effective in producing accurately resolved wall shear stress fields.





Toward Parallel, Adaptive Mesh Refinement for Chemically Reacting Flow Simulations

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Publisher :

Page : 6 pages

File Size : 33,84 MB

Release : 1997

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Adaptive numerical methods offer greater efficiency than traditional numerical methods by concentrating computational effort in regions of the problem domain where the solution is difficult to obtain. In this paper, the authors describe progress toward adding mesh refinement to MPSalsa, a computer program developed at Sandia National laboratories to solve coupled three-dimensional fluid flow and detailed reaction chemistry systems for modeling chemically reacting flow on large-scale parallel computers. Data structures that support refinement and dynamic load-balancing are discussed. Results using uniform refinement with mesh sequencing to improve convergence to steady-state solutions are also presented. Three examples are presented: a lid driven cavity, a thermal convection flow, and a tilted chemical vapor deposition reactor.