An Improved High-Resolution Discretization Scheme for Volume-of-Fluid CFD Simulations

2007 ◽  
Author(s):  
D. Keith Walters ◽  
Nicole M. Wolgemuth
Keyword(s):  
Steady State ◽  
High Resolution ◽  
Volume Fraction ◽  
Phase Interface ◽  
Volume Of Fluid ◽  
Volume Control ◽  
Test Cases ◽  
Discretization Scheme ◽  
Spatial Discretization ◽  
Interface Capturing

A new high-resolution spatial discretization scheme for use with the interface capturing volume-of-fluid (VOF) method is presented and applied to several test cases. The new scheme is shown to preserve the volume fraction discontinuity within a single computational control volume (CV), without the need to explicitly reconstruct the interface within CVs near the interface. The method is based on maximization of the volume fraction gradient in the region of the interface, while stability is preserved by maintaining net upwind biasing of the face flux prescription in each CV. In addition, the scheme employs face limiting to satisfy physical boundedness criteria at finite-volume control surfaces (faces) and prevent variable overshoot. The method has been developed for use with unstructured, anisotropic, and/or inhomogeneous meshes that are often used for simulation of geometrically complex flowfields. This paper presents the implementation of the new discretization scheme into a steady-state solver in order to isolate the spatial discretization from the time integration technique. The new scheme is validated for steady-state two-phase flow using several demonstration test cases, and is shown to preserve the phase interface almost exactly, with essentially zero dissipative or dispersive error in the volume fraction solution. Results are compared to existing 2nd order and high-resolution interface capturing (HRIC) schemes, and shown to be superior in all cases.

An Improved Bounded Gradient Maximization Method for Interface-Capturing VOF Simulations

2009 ◽  
Author(s):  
Brandon Witbeck ◽  
D. Keith Walters
Keyword(s):  
High Resolution ◽  
Phase Interface ◽  
Time Dependent ◽  
Test Cases ◽  
Discretization Scheme ◽  
Spatial Discretization ◽  
Two Phase ◽  
Initial Development ◽  
Interface Capturing ◽  
The Stability

A new high-resolution spatial discretization scheme is presented for the volume-of-fluid (VOF) method. This scheme is an adaptation of the previously published bounded gradient maximization (BGM) scheme [1]. This scheme resolves the phase interface without any explicit geometrical reconstruction of the interface. A net upwind bias in each cell ensures the stability of the scheme, and face limiting satisfies the boundedness criteria at the cell faces to prevent variable overshoot. In contrast to most existing methods, no method using “switching” between upwind-biased and downwind-biased discretization is employed to gain method stability. This paper presents the initial development and implementation of a time-dependent version of the method. Test cases are performed for a number of 2-D and 3-D two-phase flows on both structured and unstructured meshes. Results indicate that the method performs well in maintaining the resolution of the phase interface.

Application of High-Resolution Spatial Discretization Schemes to Volume-of-Fluid Simulations on Three-Dimensional Unstructured Meshes

2007 ◽  
Author(s):  
D. Keith Walters
Keyword(s):  
High Resolution ◽  
Volume Fraction ◽  
Phase Interface ◽  
Three Dimensional ◽  
Volume Of Fluid ◽  
Unstructured Meshes ◽  
Spatial Discretization ◽  
Upwind Schemes ◽  
Discretization Schemes ◽  
Control Volumes

The interface capturing approach to volume-of-fluid (VOF) simulation relies on high-resolution spatial discretization of the volume fraction equation, without explicit reconstruction of the phase interface within computational control volumes. One advantage of this approach is that it may be applied on general topology meshes in a straightforward manner. This paper investigates the performance of two different high-resolution discretization schemes used for the solution of the volume fraction equation on three-dimensional unstructured meshes. The schemes are used to obtain results for several simple test problems, including convection of a round and a square phase profile in a uniform fluid stream, two-phase oil and water flow in an inclined channel, and convection of a round jet-in-crossflow. The performance of the two schemes is compared in terms of their ability to minimize the effects of numerical dissipation, which tends to “smear” the phase interface over several computational control volumes. It is shown that a recently proposed scheme that relies on maximization of the volume fraction gradient in the region of the interface yields substantially better results than a more commonly used NVD (normalized variable diagram) based scheme, as well as traditional first and second-order upwind schemes.

Numerical Study of Advection Schemes for Interface Capturing in a Volume of Fluid Method on Unstructured Meshes

2011 ◽  
Author(s):  
Hua Shan ◽  
Sung-Eun Kim
Keyword(s):  
Free Surface ◽  
Volume Fraction ◽  
Numerical Study ◽  
Volume Of Fluid ◽  
Unstructured Meshes ◽  
Higher Order ◽  
Numerical Dispersion ◽  
Numerical Dissipation ◽  
Interface Capturing ◽  
Advection Schemes

In solving naval hydrodynamics problems using computational fluid dynamics (CFD), the moving free surface between air and water introduces extra difficulties to numerical methods, since the material property jumps across the interface and the time-dependent free surface position becomes part of the solution. Engineering applications often require a flexible and robust solver for incompressible multi-phase viscous flows with the capability of capturing the interface. In the volume of fluid (VOF) method, the interface is captured by directly solving the convection transport equation of volume fraction. In this case, the numerical dissipation of the advection scheme smears the sharp interface and the numerical dispersion causes unphysical oscillations near the interface. Utilizing the guidance of boundedness criteria, many limited higher-order non-liner advection schemes have been developed in an attempt to balance numerical dissipation and dispersion. Though it is well-known that these non-linear advection schemes can lead to solutions combining boundednesss and accuracy, users are often overwhelmed by the wide variety of available schemes. Also, these schemes are developed with the assumption of a uniform Cartesian-type mesh. Thus, a thorough investigation and comparison of the performance of these interface-capturing advection schemes are necessary, especially for naval hydrodynamics problems solved on unstructured meshes. In this study, a systematic comparison and evaluation of several existing and new bounded, higher-order advection schemes has been conducted within the framework of NavyFOAM, which is developed based on OpenFOAM — an object orientated C++ toolbox for the customization and extension of numerical solvers for continuum mechanics problems, including CFD, where the governing equations are discretized using the cell-centered finite volume method on unstructured mesh. The flexible infrastructure of the code enables us to implement and test the selected advection schemes very quickly. The test cases include advection of hollow cylinders, Zalesak’s rotating slotted disk, traveling solitary wave, dam breaking problem.

scholarly journals Cellular Automata Modeling of Ostwald Ripening and Rayleigh Instability

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1936 ◽  
Author(s):  
Fengbo Han
Keyword(s):  
Steady State ◽  
Cellular Automata ◽  
Grain Boundaries ◽  
Ostwald Ripening ◽  
Volume Fraction ◽  
Phase Interface ◽  
Growth Exponent ◽  
Phase System ◽  
Rayleigh Instability ◽  
Long Cylinder

A cellular automata (CA) approach to modeling both Ostwald ripening and Rayleigh instability was developed. Curvature-driven phase interface migration was implemented to CA model, and novel CA rules were introduced to ensure the conservation of phase volume fraction of nearly equilibrium two-phase system. For transient Ostwald ripening, it is shown that the temporal growth exponent m is evolving with time and non-integer temporal exponents between 2 and 3 are predicted. The varying temporal growth exponent m is related to the particle size distributions (PSDs) evolution. With an initial wide PSD, it becomes narrowed toward steady state. With an initial narrow PSD, it becomes widened at first and then narrowed toward steady state. For Rayleigh instability, two cases (one with sinusoidal perturbation on the surface of the long cylinder, and the other with grain boundaries in the interior of the long cylinder) were simulated, and the breakup of the long cylinder was shown for both cases. In the end, a system containing long cylinders with interior grain boundaries was simulated, which demonstrated the integration of Rayleigh instability and Ostwald ripening relating to the spheroidization of the lamellar structure.

scholarly journals Numerical Study on an Interface Compression Method for the Volume of Fluid Approach

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 80
Author(s):  
Yuria Okagaki ◽  
Taisuke Yonomoto ◽  
Masahiro Ishigaki ◽  
Yoshiyasu Hirose
Keyword(s):  
Linear Theory ◽  
Volume Fraction ◽  
Numerical Study ◽  
Volume Of Fluid ◽  
Interfacial Wave ◽  
Validation Process ◽  
Two Phase ◽  
Numerical Diffusion ◽  
Mesh Resolution ◽  
Water Reactors

Many thermohydraulic issues about the safety of light water reactors are related to complicated two-phase flow phenomena. In these phenomena, computational fluid dynamics (CFD) analysis using the volume of fluid (VOF) method causes numerical diffusion generated by the first-order upwind scheme used in the convection term of the volume fraction equation. Thus, in this study, we focused on an interface compression (IC) method for such a VOF approach; this technique prevents numerical diffusion issues and maintains boundedness and conservation with negative diffusion. First, on a sufficiently high mesh resolution and without the IC method, the validation process was considered by comparing the amplitude growth of the interfacial wave between a two-dimensional gas sheet and a quiescent liquid using the linear theory. The disturbance growth rates were consistent with the linear theory, and the validation process was considered appropriate. Then, this validation process confirmed the effects of the IC method on numerical diffusion, and we derived the optimum value of the IC coefficient, which is the parameter that controls the numerical diffusion.

scholarly journals The Influence of Different Types of Nanofluid on Thermal and Fluid Flow Performance of Liquid Cold Plate

2018 ◽  
Vol 7 (4.35) ◽  
pp. 148 ◽  
Author(s):  
Nur Irmawati Om ◽  
Rozli Zulkifli ◽  
P. Gunnasegaran
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Steady State ◽  
Pressure Drop ◽  
Volume Fraction ◽  
Cold Plate ◽  
Governing Equations ◽  
Flow And Heat Transfer ◽  
Different Types ◽  
Volume Method

The influence of utilizing different nanofluids types on the liquid cold plate (LCP) is numerically investigated. The thermal and fluid flow performance of LCP is examined by using pure ethylene glycol (EG), Al2O3-EG and CuO-EG. The volume fraction of the nanoparticle for both nanofluid is 2%. The finite volume method (FVM) has been used to solved 3-D steady state, laminar flow and heat transfer governing equations. The presented results indicate that Al2O3-EG able to provide the lowest surface temperature of the heater block followed by CuO-EG and EG, respectively. It is also found that the pressure drop and friction factor are higher for Al2O3-EG and CuO-EG compared to the pure EG.

scholarly journals WATERSHED SPATIAL DISCRETIZATION FOR THE ANALYSIS OF LAND USE CHANGE IN COASTAL REGIONS

2017 ◽  
Vol 23 (1) ◽  
pp. 101-114 ◽  
Author(s):  
Vassiliki Terezinha Galvão Boulomytis ◽  
Antonio Carlos Zuffo ◽  
Tiago Zenker Gireli
Keyword(s):  
Land Use ◽  
High Resolution ◽  
Extraction Process ◽  
Surface Model ◽  
Terrain Analysis ◽  
Spatial Discretization ◽  
Tidal Variation ◽  
Flood Vulnerability ◽  
Elevation Model ◽  
Geotechnical Risk

In this study, we present a methodology to discretize a non-assessed basin based on terrain analysis using the SRTM digital elevation model (DEM) and a high resolution surface model (DSM) with a drainage network semi-automatic extraction process. The Juqueriquerê River Basin was used for the case study, which has the most representative non-urbanized plains of the northern coastline of São Paulo State, Brazil. The low-lying region is featured by elevations close to the sea level, mild slopes, and shallow water tables. It is also influenced by tidal variation and orographic rains. Therefore, frequent flooding occurs, even in vegetated areas. Two conflicting land use scenarios, proposed by the City Master Plan (CMP) of Caraguatatuba and the Ecological-Economical Zoning (EEZ), were compared to analyze the flood vulnerability increase and geotechnical risk caused by the urbanization process. The drainage extraction techniques showed better results on high resolution DSM for low-lying regions than the SRTM DEM and determined with accuracy the locations of flood potentiality in the plains. The watershed spatial discretization allowed us to show the effects of the two different land use approaches, considering the flood vulnerability and geotechnical risk of each sub-basin

scholarly journals STEADY-STATE MODELLING OF PEM FUEL CELLS USING GRADIENT-BASED OPTIMIZER

10.6036/10099 ◽  
2021 ◽  
Vol DYNA-ACELERADO (0) ◽  
pp. [ 8 pp.]-[ 8 pp.]
Author(s):  
SALAH KAMAL ◽  
ATTIA EL-FERGANY ◽  
EHAB EHAB ELSAYED ELATTAR ◽  
AHMED AGWA
Keyword(s):  
Fuel Cells ◽  
Steady State ◽  
Fuel Cell ◽  
Optimization Problem ◽  
Pem Fuel Cells ◽  
Test Cases ◽  
Uncertain Parameters ◽  
Gradient Based ◽  
High Degree ◽  
Exchange Membrane

The accuracy of fuel cell (FC) models is important for the further numerical simulations and analysis at several conditions. The electrical (I-V) characteristic of the polymer exchange membrane fuel cells (PEMFCs) has high degree of nonlinearity comprising uncertain seven parameters as they aren’t given in fabricator's datasheets. These seven parameters need to be obtained to have the PEMFC model in order. This research addresses an up-to-date application of the gradient-based optimizer (GBO) to generate the best estimated values of such uncertain parameters. The estimation of these uncertain parameters is adapted as optimization problem having a cost function (CF) subjects to set of self-constrained limits. Three test cases of widely used PEMFCs units; namely, SR-12, 250-W module and NedStack PS6 to appraise the performance of the GBO are demonstrated and analyzed. The best values of the CF are 0.000142, 0.33598, and 2.10025 V2 for SR-12, 250-W module and NedStack PS6; respectively. Furthermore, the assessment of the GBO-based model is made by comparing its obtained results with the experiential results of these typical PEMFCs plus comparisons to other methods. At a due stage, many scenarios as a result of operating variations in regard to inlet regulation pressures and unit temperatures are performed. The copped reported results of the studied scenarios indicate the effectiveness of the GBO in establishing an accurate PEMFC model.

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