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Cascade arc studies of hydrogen/nitrogen plasmas in nonequilibrium

JOURNAL OF PROPULSION AND POWER 2002年第1期18卷 176-183页

作者： Moeller, T Keefer, D Rhodes, R Univ Tennessee Inst Space Tullahoma TN 37388 USA

A cascade arc facility was developed to study the characteristics of nonequilibrium plasma propellants for electric propulsion applications. The cascade arc was operated with 50 A hydrogen arcs at absolute pressures of 1.34 x 10(4) and 4.14 x 10(4) Pa. Spatially resolved spectral emission data were collected using a two-dimensional optical multichannel analyzer (OMA), and radial distributions of H-alpha line widths of the Abel inverted emission line profiles were obtained. The measured H-alpha line widths were compared to values predicted by nonequilibrium cascade are simulations using the UTSI Cascade Arc Plasma Simulation (CAPS) code and dynamic ion Stark broadening/electron number density correlations. Agreement was sensitive to the finite-rate kinetic model used for hydrogen. When used in CA-PS, University of Illinois kinetics model gave the best agreement with the hydrogen cascade arc measurements. The experimental electric field and radially resolved H-alpha line widths accurately predicted measured values at both pressures within experimental uncertainty. H-alpha line widths for simulated ammonia and hydrazine were also obtained at pressures of 1.34 x 10(4), 4.14 x 10(4), and 6.89 x 10(4) Pa. These mixture data can be used for future evaluations of kinetic models for hydrogen/nitrogen mixtures.

关键词： Nonequilibrium Plasmas Thermal Conductivity Propellant Chemical Kinetics Electric Propulsion simple algorithm Ohmic Heating Spectrometers Conservation Equations Activation Energy

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Solution of transport equations on unstructured meshes with cell-centered colocated variables. Part I: Discretization

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2005年第6期48卷 1117-1127页

作者： Date, AW Indian Inst Technol Dept Mech Engn Bombay 400076 Maharashtra India

This paper describes discretization of transport equations on unstructured meshes with cell-centered colocated variables. The problem of zig-zag pressure prediction is eliminated by introducing smoothing pressure correction derived by Date [A.W. Date, Complete pressure correction algorithm for solution of incompressible Navier-Stokes equations on a non-staggered grid, Numer. Heat Transfer, Part B 29 (1995) 441-458]. The finite-volume discretization is carried out in a structured grid like manner by invoking a special line-structure to evaluate convective-diffusive transport across the cell-faces. (C) 2004 Elsevier Ltd. All rights reserved.

关键词： simple algorithm smoothing pressure correction unstructured meshes colocated variables line-structure

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Spatiotemporal distribution of rainfall erosivity in the Yanhe River watershed of hilly and gully region, Chinese Loess Plateau

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ENVIRONMENTAL EARTH SCIENCES 2016年第4期75卷 1-13页

作者： Wu, Lei Liu, Xia Ma, Xiao-yi Northwest A&F Univ State Key Lab Soil Eros & Dryland Farming Loess P Xianyang 712100 Shaanxi Peoples R China Northwest A&F Univ Coll Water Resources & Architectural Engn 23 Weihui Rd Xianyang 712100 Shaanxi Peoples R China Northwest A&F Univ Key Lab Agr Soil & Water Engn Arid Reg Minist Educ Xianyang 712100 Shaanxi Peoples R China Northwest A&F Univ Construct Dept Xianyang 712100 Shaanxi Peoples R China

Rainfall erosivity is considered as one of the most important factors in the universal soil loss equation (USLE) or its revised form (RUSLE);it can directly reflect the potential of soil erosion caused by rainfall. In this study, the simple algorithms of rainfall erosivity including the Wischmeier model and the half-month model are selected and used to estimate rainfall erosivity values from 1971 to 2013 in the Yanhe River watershed of the hilly and gully region, Chinese Loess Plateau. Results demonstrate that: (1) the applicability of the simple algorithms of rainfall erosivity in loess hilly and gully region is good and the half-month model is more suitable for the Yanhe River watershed;(2) the overall variations of annual rainfall erosivity values estimated by the two models are similar and show a decreased trend during the relatively steady rainfall period from 1971 to 2012;but they will have a certain degree of deviation for the extreme rainfall with high intensity and short duration in 2013;the monthly variations of rainfall erosivity within a year are highly concentrated in 5-10 months, the rainfall erosivity in other months are almost zero;(3) the spatial distributions of the rainfall erosivity have strong correlation with the erosive rainfall, precipitation and rainfall erosivity which both present an increasing trend from northwest to southeast in the Yanhe River watershed;the central and southern regions both have the highest rainfall and the most serious erosivity;and both rainfall and erosivity in southeast are more serious than that in northwest of the watershed. Results may provide scientific theoretical guidance and data support for soil loss management of the hilly and gully region, Chinese Loess Plateau.

关键词： Rainfall erosivity simple algorithm Spatiotemporal distribution Yanhe River watershed Loess Plateau

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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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A new numerical method for solution of boiling flow using combination of simple and Jacobian-free Newton-Krylov algorithms

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PROGRESS IN NUCLEAR ENERGY 2017年 95卷 48-60页

作者： Hajizadeh, A. Kazeminejad, H. Talebi, S. Nucl Sci & Technol Res Inst Res Sch Reactor POB 11365-3486 Tehran Iran Nucl Sci & Technol Res Inst Res Sch Radiat Applicat POB 11365-3486 Tehran Iran Amirkabir Univ Technol Tehran Polytech Dept Energy Engn & Phys 424 Hafez AvePOB 15875-4413 Tehran Iran

In this paper, an efficient and stable numerical approach is developed in which a different combination of Jacobian-free Newton-Krylov (JFNK) and simple methods are introduced for solution of two-phase flow in both steady state and transient conditions. It is shown that, combination of Krylov subspace methods and simple type preconditioner give a fast convergence in the solution of the Drift Flux Model (DFM). It is demonstrated that the stability problem with simple approach, for two-phase flow problems, can be avoided by combining with JFNK. RELAP5 code and experimental data are considered for verification study. For all benchmarks, the proposed methods predictions are in good agreement with experiment and RELAP5 results. The accuracy of the proposed schemes were studied and compared with the classical simple method. It was found that the present approach to two-phase flow simulation predicts accurate results over a wide pressure range;whereas the classical simple algorithm underestimated the void fraction at low pressures. Finally, a typical power transient is considered to derrionstrate how the problem fastest time scale can change during the course of a transient. The present assessment of the numerical method showed that the time step control is not based on a stability time step restriction, like the material Courant limit. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Drift flux model simple algorithm Jacobian-free Newton-Krylov method

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The effect of the VOF-CSF static contact angle boundary condition on the dynamics of sliding and bouncing ellipsoidal bubbles

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INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW 2011年第5期32卷 964-972页

作者： Senthilkumar, S. Delaure, Y. M. C. Murray, D. B. Donnelly, B. Dublin City Univ Sch Mech & Mfg Engn Dublin 9 Ireland Trinity Coll Dublin Dept Mech & Mfg Engn Dublin Ireland

The static contact angle is the only empiricism introduced in a Volume of Fluid-Continuum Surface Force (VOF-CSF) model of bubbly flow. Although it has previously been shown to have a relatively limited effect on the accuracy of velocity and shape predictions in the case of large gas bubbles sliding under inclined walls (e.g. Cook and Behnia, 2001), it may have a more determining influence on the numerical prediction of the dynamics of smaller ellipsoidal bubbles which were shown by Tsao and Koch (1997) to bounce repeatedly when sliding under inclined walls at certain wall inclinations. The present paper reports on the influence of surface tension and the static contact angle on the dynamics of an ellipsoidal air bubble of equivalent diameter D-e = 3.4 mm. The bubble Eat-vas and Morton numbers are Eo = 1.56 and Mo = 2 x 10(-11) respectively. The computational results are achieved with a Piecewise Linear Construction (PLIC) of the interface and are reviewed with reference to experimental measurements of bubble velocity and interface shape oscillations recorded using a high speed digital camera. Tests are performed at plate inclination angles theta is an element of {10 degrees,20 degrees,30 degrees,45 degrees) to the horizontal and computational models consider three static contact angles theta(c) is an element of {10 degrees,20 degrees,30 degrees). The static contact angle has been found to have a significant effect on the bubble dynamics but to varying degree depending on the plate inclination. It is shown to promote lift off and bouncing when the plate inclination angle reaches 30 degrees in a way that does not necessarily reflect experimental observations. (C) 2011 Elsevier Inc. All rights reserved.

关键词： Gas-liquid flow Sliding bubble Volume-of-Fluid PLIC method simple algorithm Static contact angle

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Numerical simulations of the flow field around the rings of mechanical seals

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JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME 2006年第3期128卷 559-565页

作者： Luan, Zhaogao Khonsari, M. M. Louisiana State Univ Dept Mech Engn Baton Rouge LA 70803 USA

The flow inside a seal chamber as induced by the influx of the flush fluid and the rotation of the primary ring is analyzed. The 3-D flow characteristic around the mating ring and the rotating ring are predicted by solving the Navier-Stokes equations in cylindrical coordinates. For this purpose, the pressure correction method was used in conjunction with the simple algorithm. A series of numerical solutions is presented that show the flow mechanism within the gap between the rings and the gland. The implication of the flow characteristic on the cooling of the rings is discussed.

关键词： mechanical seal flow field CFD simple algorithm pressure correction method

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Comparison of simple- and PISO-type algorithms for transient flows

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INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 1998年第4期26卷 459-483页

作者： Barton, IE Univ Cambridge Dept Engn Div A CFD Lab Cambridge CB2 1PZ England

Various pressure-based schemes are proposed for transient flows based on well-established simple and PISO algorithms. The schemes are applied to the solution of unsteady laminar how around a square cylinder and steady laminar flow over a backward-facing step. The implicit treatment and the performance of the various schemes are evaluated by using benchmark solutions with a small time step. Three different second-order-accurate time derivatives based on different time levels are presented. The different time derivatives are applied to the various schemes under consideration. Overall the PISO scheme was found to predict accurate results and was robust. However, for small time step values, alternative schemes can predict accurate results for approximately half the computational cost. The choice of time derivative proved to be very significant in terms of the accuracy and robustness of a scheme. Significantly, the one-sided forward differencing scheme was the most successful used in conjunction with a strongly implicit-based algorithm. However, a greater degree of accuracy was achieved using the standard PISO algorithm with the Crank-Nicolson time derivative. Recommendations for future work are discussed. (C) 1998 John Wiley & Sons, Ltd.

关键词： simple algorithm PISO algorithm unsteady incompressible flow

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A simple based discontinuous Galerkin solver for steady incompressible flows

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JOURNAL OF COMPUTATIONAL PHYSICS 2013年 237卷 235-250页

作者： Klein, Benedikt Kummer, Florian Oberlack, Martin Tech Univ Darmstadt Dept Mech Engn Chair Fluid Dynam D-64287 Darmstadt Germany Tech Univ Darmstadt Ctr Smart Interfaces D-64287 Darmstadt Germany Tech Univ Darmstadt Grad Sch Computat Engn D-64293 Darmstadt Germany

In this paper we present how the well-known simple algorithm can be extended to solve the steady incompressible Navier-Stokes equations discretized by the discontinuous Galerkin method. The convective part is discretized by the local Lax-Friedrichs fluxes and the viscous part by the symmetric interior penalty method. Within the simple algorithm, the equations are solved in an iterative process. The discretized equations are linearized and an equation for the pressure is derived on the discrete level. The equations obtained for each velocity component and the pressure are decoupled and therefore can be solved sequentially, leading to an efficient solution procedure. The extension of the proposed scheme to the unsteady case is straightforward, where fully implicit time schemes can be used. Various test cases are carried out: the Poiseuille flow, the channel flow with constant transpiration, the Kovasznay flow, the flow into a corner and the backward-facing step flow. Using a mixed-order formulation, i.e. order k for the velocity and order k - 1 for the pressure, the scheme is numerically stable for all test cases. Convergence rates of k + 1 and k in the L-2-norm are observed for velocity and pressure, respectively. A study of the convergence behavior of the simple algorithm shows that no under-relaxation for the pressure is needed, which is in strong contrast to the application of the simple algorithm in the context of the finite volume method or the continuous finite element method. We conclude that the proposed scheme is efficient to solve the steady incompressible Navier-Stokes equations in the context of the discontinuous Galerkin method comprising hp-accuracy. (c) 2012 Elsevier Inc. All rights reserved.

关键词： Finite element methods Discontinuous Galerkin methods Navier-Stokes equations Incompressible flows Segregated solution algorithms simple algorithm

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