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Implementation of a smoothing pressure correction approach to the pressure-correction equation in order to maintain the use of simpleC algorithms on non-staggered grids

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PROGRESS IN COMPUTATIONAL FLUID DYNAMICS 2010年第1期10卷 40-50页

作者： Anany, M. N. Schnell, U. Scheffknecht, G. Univ Stuttgart Inst Proc Engn & Power Plant Technol D-70569 Stuttgart Germany

Date (1996) introduced a pressure-correction equation containing mass-conserving and smoothing pressure correction terms to solve the Navier-Stokes equations. The benefit of the smoothing terms is satisfying the stokes's relation which is often overlooked as well as overcoming the decoupling problem of the pressure-velocity fields, which renders it applicable to collocated (non-staggered) grids. His derivation relied on assumptions relevant to the simple algorithm (Caretto et al., 1972). Such assumptions are, unfortunately, not directly applicable to simpleC procedures (van Doormaal and Raithby, 1984). The main purpose of this paper is to extend the pressure-correction equation proposed by Date (1996) to simpleC algorithms.

关键词： colocated grid collocated grid non-staggered grid simple algorithm simpleC algorithm smoothing pressure corrections

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The influence of grid orthogonality on the convergence of the simple algorithm for solving Navier-Stokes equations

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STROJNISKI VESTNIK-JOURNAL OF MECHANICAL ENGINEERING 2007年第2期53卷 105-113页

作者： Dzijan, Ivo Virag, Zdravko Kozmar, Hrvoje Univ Zagreb Fac Mech Engn & Naval Architecture HR-10000 Zagreb Croatia

A finite-volume method for solving the Navier-Stokes equations on a locally orthogonal unstructured grid using the simple algorithm has been developed. The developed method was compared with a similar method on a structured, not necessarily orthogonal grid, in terms of convergence history and the range of under-relaxation factors in which the methods converge. When the structured grid is orthogonal, the convergence rates of the two methods are similar For the cases when the structured grid is non-orthogonal, the superiority of the proposed method on the locally orthogonal grid is demonstrated in terms of convergence history. In these cases, the range of under-relaxation factors in which the proposed method shows satisfactory convergence is much wider than for the method on the non-orthogonal grid. (c) 2007 Journal of Mechanical Engineering. All rights reserved.

关键词： Navier-Stokes equations finite volume methods simple algorithm unstructured grid

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Temperature-explicit formulation of energy equation for thermal-hydraulic analyses

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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER 2010年第3期37卷 256-260页

作者： Kim, Jongtae Ha, Kwang Soon Kim, Sang-Baik Korea Atom Energy Res Inst Dept Thermal Hydraul Safety Res Taejon 305353 South Korea

A temperature equation which is derived from an enthalpy transport equation by using an assumption of a constant specific heat is very attractive for analyses of heat and fluid flows. It can be used for an analysis of a solid-fluid conjugate heat transfer, and it does not need a numerical method to obtain temperature from a temperature-enthalpy relation. But its application is limited because of the assumption. A new method is derived in this study, which is a temperature-explicit formulation of the energy equation. The enthalpy form of the energy equation is used in the method. But the final discrete form of the equation is expressed with temperature. The discretized equation from the temperature-explicit formulation can be used for a heat transfer analysis in a solid-fluid coupled region without any special treatment at the solid-fluid interface. And it can be applied for multiphase flows with a real gas effect. It is found by numerical tests in this study that the proposed method is very efficient and as accurate as the standard enthalpy formulation. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Segregated method simple algorithm Energy equation Temperature form Enthalpy form Temperature-explicit formulation

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Modeling and simulation of microfluid effects on deformation behavior of a red blood cell in a capillary

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MICROVASCULAR RESEARCH 2010年第3期80卷 453-463页

作者： Ye, Ting Li, Hua Lam, K. Y. Nanyang Technol Univ Sch Mech & Aerosp Engn Singapore 639798 Singapore

A modified SIMPER algorithm is developed for analysis of microfluid effects on the motion and deformation of a red blood cell (RBC) in a capillary. With consideration of very small Reynolds number in microfluidics, this algorithm not only speeds up the convergence of the momentum equations by combining the advantages of the simpleC and simpleR algorithms together, but also satisfies the continuity equation with higher accuracy by integrating a fine adjustment technique. In order to validate the modified simpleR algorithm, the behavior of RBC in a capillary is simulated at different velocities. When the mean RBC velocity is 0.1 mm/s, the RBC exhibits a characteristic parachute shape in the steady state, which agrees well with the numerical results previously reported. Apart from that, a quantitative validation with the experimental data is performed by examining the relationship between the mean velocity and deformation index of the RBC, showing an excellent agreement. The effects of crucial parameters are investigated systematically on the motion and deformation of the RBC, including the RBC radius, elastic modulus and bending stiffness of RBC membrane, initial velocity of suspending fluid, as well as the density and viscosity ratios of the suspending fluid to RBC. The simulation results demonstrate that all of the parameters have influences on the RBC behavior by changing the interaction between the RBC and suspending fluid. (C) 2010 Elsevier Inc. All rights reserved.

关键词： simple algorithm Front tracking method Two-fluid flow RBC deformation Computational fluid dynamics

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Two-dimensional modeling of selective CO oxidation in a hydrogen-rich stream

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2010年第17期35卷 9504-9509页

作者： Akbari, M. H. Vahabi, M. Shiraz Univ Fuel Cell Res Ctr Fac Mech Engn Shiraz Iran

In this study, carbon monoxide removal by preferential oxidation in a hydrogen-rich stream is simulated between two parallel infinite plates of 150 mu m distance. A three-step kinetic is considered that includes carbon monoxide oxidation, hydrogen oxidation and water gas shift reaction. The walls temperature is in the range of 80-120 degrees C. The function of this microreactor is to reduce carbon monoxide content from about 2% to below 10 ppm, suitable for use in a PEM fuel cell. Based on the problem conditions, the flow is in the continuum regime and application of the Navier Stokes equations is admissible. In order to simulate the reacting flow, continuity, conservations of x- & y-momentum, conservation of energy, conservation of species, state equation and reaction rates are simultaneously solved through simple algorithm by utilizing power-law scheme. Effects of important parameters including walls temperature, steam content, CO content and O(2)/CO are assessed. It is observed that increasing walls temperature or oxygen content will increase both CO selectivity and conversion. It is also found that by steam addition, CO conversion is improved without significant change of CO selectivity. These results are in good agreement with previous published data. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

关键词： Fuel processing Microreactor Selective CO oxidation CFD simple algorithm 2D modeling

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Numerical Simulation of the cooling effect by air conditioner and spraying in high-temperature working face

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International Conference on Manufacturing Science and Engineering (ICMSE 2009)

作者： Liu Guan-nan Gao Feng Ji Ming Liu Xing-guang China Univ Min & Technol Coll Sci Xuzhou 221000 Peoples R China

ISBN: (纸本)9780878492800

A multicomponent turbulent model of the airflow in working face was modeled. And the simulation result is compared with the measured temperature. The temperature of the airflow along the transportation channel of working face goes up,and the gradient of the temperature curve is flat. Then the low-temperature droplets are simulated by stochastic separated flow model. The interaction between grains and fluid are simulated by adding source terms in conservation equations. The temperature curves of the airflow under different cooling schemes are investigated if the air conditioner is in front of the nozzles,the temperature of the air near the inlet is low and uniform,and the cooling effect of the outlet is obvious.

关键词： stochastic model working face temperature field simple algorithm

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Improvement of Free Convection Heat Transfer Rate of Rectangular Heatsink on Vertical Base Plates

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Energy and Power Engineering 2011年第4期3卷

作者： Hamid Reza Goshayeshi Mahdi Fahiminia Mohammad Mahdi Naserian Department of Mechanical Engineering Mashhad Branch Islamic Azad University Young Researchers Club Mashhad Branch Islamic Azad University

In this paper, the laminar heat transfer of natural convection on vertical surfaces is investigated. Most of the studies on natural convection have been considered constantly whereas velocity and temperature domain, do not change with time, transient one are used a lot. Governing equations are solved using a finite volume ap- proach. The convective terms are discretized using the power-law scheme, whereas for diffusive terms the central difference is employed. Coupling between the velocity and pressure is made with simple algorithm. The resultant system of discretized linear algebraic equations is solved with an alternating direction implicit scheme. Then a configuration of rectangular fins is put in different ways on the surface and heat transfer of natural convection on these surfaces without sliding is studied and finally optimization is investigated.

关键词： Natural Convection Vertical Surfaces simple algorithm Rectangular Fins

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Two-dimensional modeling of selective CO oxidation in a hydrogen-rich stream

Two-dimensional modeling of selective CO oxidation in a hydr...

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1st National Conference on Hydrogen and Fuel Cell (H2FC2009)

作者： Akbari, M. H. Vahabi, M. Shiraz Univ Fuel Cell Res Ctr Fac Mech Engn Shiraz Iran

关键词： Fuel processing Microreactor Selective CO oxidation CFD simple algorithm 2D modeling

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Formulation of fully implicit method for simulation of flows with interfaces using primitive variables

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2009年第13-14期52卷 3217-3224页

作者： Nandi, Kausik Date, A. W. Indian Inst Technol Dept Mech Engn Mumbai 400076 Maharashtra India

This paper is concerned with simulation of flows with interface between two incompressible and immiscible fluids on a fixed grid using what is called the single fluid formalism. This formalism views flow of two fluids as that of a single fluid whose density and viscosity change abruptly at the interface. The location of the interface is option not known but is to be discovered as part of the solution. Problems of this type are typically solved using an equation for (a) Volume Fraction or, for (b) Level Set function. In the present paper, the governing Navier-Stokes equations in primitive variables are solved on collocated grids using simple algorithm with a specially derived smoothing pressure correction that satisfies volume conservation. A superficial density is defined and determined from mass conservation equation. It is shown that this equation can be cast in the form of a well-known volume fraction equation. The interface location is determined without interface reconstruction. The convective terms are represented by a TVD scheme to predict less-smeared interface. The surface tension force is evaluated by two methods via geometric and fluid dynamic evaluation of the interface curvature. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Single fluid formalism Surface tension force Collocated fixed grid simple algorithm

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Three-dimensional simulation and optimization of an isothermal PROX microreactor for fuel cell applications

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2009年第3期34卷 1531-1541页

作者： Vahabi, M. Akbari, M. H. Shiraz Univ Dept Mech Engn Fuel Cell Res Ctr Shiraz *** Iran

Three-dimensional numerical simulations of the reacting flow in rectangular microchannel PROX reactors are performed. To solve the set of governing equations, a finite volume method is applied using an improved simple algorithm. A three-step surface kinetics for the chemical reactions is utilized that includes hydrogen oxidation, carbon monoxide oxidation, and water-gas shift reaction. The kinetics chosen are for a Pt-Fe/gamma-Al2O3 catalyst and operating temperatures of about 100 degrees C. The PROX reactor is expected to remove the carbon monoxide content in a hydrogen-rich stream from about 2% to less than 10 ppm. Effects of the inlet steam content, oxygen to carbon monoxide ratio, reactor wall temperature, aspect ratio of the channel cross section, and the channel hydraulic diameter are investigated. It is found that increasing the steam content, oxygen to carbon monoxide ratio, or wall temperature may improve the performance of the microreactor. it is also shown that the rate of water-gas shift reaction or its reverse is much lower than the oxidation reactions. Finally, it is revealed that based on a modified CO yield definition, the optimum channel geometry is a square shape. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

关键词： Hydrogen production PROX Microreactor CO selectivity Conversion Yield Finite volume method simple algorithm

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