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The modeling of a laboratory natural gas-fired furnace with a higher-order projection method for unsteady combustion

Description: A higher-order, embedded boundary projection method for axisymmetric, unsteady, low-Mach number combustion is used to model a natural gas flame from a 300 kW IFRF burner in the Burner Engineering Research Laboratory (BERL) at Sandia National Laboratory under hot wall conditions. The numerical predictions presented are the late simulated-time results of a computation of unsteady flow in the furnace. The predictions are compared both with measurements completed in the BERL as part of the GRI SCALING 400 Project and with results from a steady-state axisymmetric reacting flow code in order to evaluate the combustion model and the numerical method. The results compare favorably with the experimental data.
Date: February 1, 1996
Creator: Pember, R.B.; Colella, P.; Howell, L.H. & Almgren, A.S.
Partner: UNT Libraries Government Documents Department

A Comparison of Staggered-Mesh Lagrange Plus Remap and Cell-Centered Direct Eulerian Godunov Schemes for Rulerian Shock Hydrodynamics

Description: We present a comparison of two algorithms for solving the equations of unsteady inviscid compressible flow in a Eulerian frame. The first algorithm is a staggered grid Lagrange plus remap scheme. The Lagrange step in this method is a time-centered version of the scheme due to Tipton, while the remap step employs a variant of the corner transport upwind scheme due to Colella. The second algorithm is a spatially operator-split version of the higher-order Godunov scheme for gas dynamics due to Colella. They use the two methods to compute solutions to a number of one- and two-dimensional problems. The results show the accuracy and performance of the two schemes to be generally equivalent. In a 1984 survey paper by Woodward and Colella, staggered grid, Lagrange plus remap, artificial viscosity schemes did not compare favorably with cell-centered direct Eulerian higher-order Godunov methods. They examine, therefore, how certain features of the staggered grid scheme discussed here contribute to its improved accuracy. They show in particular that the improved accuracy of the present scheme is due in part to the use of a monotonic artificial viscosity in the Lagrange step and the use of an improved upwind method in the remap step.
Date: November 22, 2000
Creator: Pember, R.B. & Anderson, R.W.
Partner: UNT Libraries Government Documents Department

Induction time effects in pulse combustors

Description: Combustion systems that take advantage of a periodic combustion process have many advantages over conventional systems. Their rate of heat transfer is greatly enhanced and their pollutant emissions are lower. They draw in their own supply of fuel and air and they are self-venting. They have few moving parts. The most common type of pulse combustor is based on a Helmholtz resonator - a burning cycle drives a resonant pressure wave, which in turn enhances the rate of combustion, resulting in a self-sustaining, large-scale oscillation. Although the basic physical mechanisms controlling such a process were explained by Rayleigh over a century ago, a full understanding of the operation of a pulse combustor still does not exist. The dominant processes in such a system--combustion, turbulent fluid dynamics, acoustics--are highly coupled and interact nonlinearly, which has reduced the design process to a costly and inefficient trial-and-error procedure. Several recent numerical and experimental studies, however, have been focused towards a better understanding of the basic underlying physics. Barr et al. [l] have elucidated the relative roles of the time scales governing the energy release, the turbulent mixing, and the acoustics. Keller et al. [5] have demonstrated the importance of the phase relation between the resonant pressure field in the tailpipe and the periodic energy release. Marcus et al. [6] have developed the capability for a fully three-dimensional simulation of the reacting flow in a pulse combustor. This paper is an application of that methodology to a detailed investigation of the frequency response of the model to changes in the chemical kinetics. The methodology consists of a fully conservative second-order Godunov algorithm for the inviscid, reacting gas dynamics equations coupled to an adaptive mesh refinement procedure[2]. The axisymmetric and three-dimensional simulations allow us to explore in detail the interaction between the transient fluid dynamics ...
Date: April 9, 1999
Creator: Bell, J B; Marcus, D L & Pember, R B
Partner: UNT Libraries Government Documents Department

An adaptive mesh refinement algorithm for the discrete ordinates method

Description: The discrete ordinates form of the radiative transport equation (RTE) is spatially discretized and solved using an adaptive mesh refinement (AMR) algorithm. This technique permits the local grid refinement to minimize spatial discretization error of the RTE. An error estimator is applied to define regions for local grid refinement; overlapping refined grids are recursively placed in these regions; and the RTE is then solved over the entire domain. The procedure continues until the spatial discretization error has been reduced to a sufficient level. The following aspects of the algorithm are discussed: error estimation, grid generation, communication between refined levels, and solution sequencing. This initial formulation employs the step scheme, and is valid for absorbing and isotopically scattering media in two-dimensional enclosures. The utility of the algorithm is tested by comparing the convergence characteristics and accuracy to those of the standard single-grid algorithm for several benchmark cases. The AMR algorithm provides a reduction in memory requirements and maintains the convergence characteristics of the standard single-grid algorithm; however, the cases illustrate that efficiency gains of the AMR algorithm will not be fully realized until three-dimensional geometries are considered.
Date: March 1, 1996
Creator: Jessee, J.P.; Fiveland, W.A.; Howell, L.H.; Colella, P. & Pember, R.B.
Partner: UNT Libraries Government Documents Department

An embedded boundary method for the modeling of unsteady combustion in an industrial gas-fired furnace

Description: A new methodology for the modeling of unsteady, nonpremixed, axisymmetric reacting flow in industrial furnaces is presented. The method is an extension of previous work by the authors to complex geometries, multistep kinetics mechanisms, and realistic properties, especially thermochemical data. The walls of the furnace are represented as an embedded boundary in a uniform, rectangular grid. The grid then consists of uniform rectangular cells except at the furnace wall where irregular (mixed) cells may be present. We use finite volume differencing techniques for the convective, viscous, and radiative heat transport terms in the mixed cells, while a finite element-based technique is used to solve the elliptic equation arising from the low-Mach number formulation. Results from the simulation of an experimental natural gas-fired furnace are shown.
Date: October 18, 1995
Creator: Pember, R.B.; Almgren, A.S.; Crutchfield, W.Y.; Howell, L.H.; Bell, J.B.; Colella, P. et al.
Partner: UNT Libraries Government Documents Department

An adaptive projection method for the modeling of unsteady, low-Mach number combustion

Description: In this paper the authors present an adaptive projection method for modeling unsteady, low-Mach reacting flow in an unconfined region. The equations they solve are based on a model for low-Mach number combustion that consists of the evolution equations for density, species concentrations, enthalpy, and momentum coupled with a constraint on the divergence of the flow. The algorithm is based on a projection methodology in which they first advance the evolution equations and then solve an elliptic equation to enforce the divergence constraint. The adaptive mesh refinement (AMR) scheme uses a time-varying, hierarchical grid structure composed of uniform rectangular grids of varying resolution. The integration scheme on the grid hierarchy is a recursive procedure in which a coarse grid is advanced, fine grids are advanced multiple steps to reach the same time as the coarse grid, and the coarse and the fine grids are synchronized. The method is valid for multiple grids on each level and multiple levels of refinement. The method is currently implemented for laminar, axisymmetric flames with a reduced kinetics mechanism and a Lewis number of unity. Two methane-air flames, one steady and the other flickering, are presented as numerical examples.
Date: October 1, 1997
Creator: Pember, R.B.; Howell, L.H.; Bell, J.B.; Colella, P.; Crutchfield, W.Y.; Fiveland, W.A. et al.
Partner: UNT Libraries Government Documents Department

A higher-order projection method for the simulation of unsteady turbulent nonpremixed combustion in an industrial burner

Description: The modeling of transient effects in burners is becoming increasingly important. The problem of ensuring the safe performance of an industrial burner, for example, is much more difficult during the startup or shutdown phases of operation. The peak formation of pollutants is also much more dependent on transient behavior, in particular, on peak temperatures, than on average operating conditions. In this paper we present a new methodology for the modeling of unsteady, nonpremixed, reacting flow in industrial burners. The algorithm uses a second-order projection method for unsteady, low-Mach number reacting flow and accounts for species diffusion, convective and radiative heat transfer, viscous transport, turbulence, and chemical kinetics. The time step used by the method is restricted solely by an advective CFL condition. The methodology is applicable only in the low-Mach number regime (M < .3), typically met in industrial burners. The projection method for low-Mach number reacting flow is an extension of a higher-order projection method for incompressible flow [9, 5, 3,4] to the low-Mach number equations of reacting flow. Our method is based on an approximate projection formulation. Radiative transport is modeled using the discrete ordinates method. The main goal of this work is to introduce and investigate the simulation of burners using a higher-order projection method for low-Mach number combustion. As such, the methodology is applied here only to axisymmetric flow in gas-fired burners for which the boundaries can be aligned with a rectangular grid. The perfect gas law is also assumed. In addition, we use a one-step reduced kinetics mechanism, a {kappa} {minus} {epsilon} model for turbulent transport, and a simple turbulent combustion model.
Date: December 1, 1994
Creator: Pember, R. B.; Almgren, A. S.; Bell, J. B.; Colella, P.; Howell, L. & Lai, M.
Partner: UNT Libraries Government Documents Department

An adaptive multifluid interface-capturing method for compressible flow in complex geometries

Description: We present a numerical method for solving the multifluid equations of gas dynamics using an operator-split second-order Godunov method for flow in complex geometries in two and three dimensions. The multifluid system treats the fluid components as thermodynamically distinct entities and correctly models fluids with different compressibilities. This treatment allows a general equation-of-state (EOS) specification and the method is implemented so that the EOS references are minimized. The current method is complementary to volume-of-fluid (VOF) methods in the sense that a VOF representation is used, but no interface reconstruction is performed. The Godunov integrator captures the interface during the solution process. The basic multifluid integrator is coupled to a Cartesian grid algorithm that also uses a VOF representation of the fluid-body interface. This representation of the fluid-body interface allows the algorithm to easily accommodate arbitrarily complex geometries. The resulting single grid multifluid-Cartesian grid integration scheme is coupled to a local adaptive mesh refinement algorithm that dynamically refines selected regions of the computational grid to achieve a desired level of accuracy. The overall method is fully conservative with respect to the total mixture. The method will be used for a simple nozzle problem in two-dimensional axisymmetric coordinates.
Date: April 1, 1995
Creator: Greenough, J.A.; Beckner, V.; Pember, R.B.; Crutchfield, W.Y.; Bell, J.B. & Colella, P.
Partner: UNT Libraries Government Documents Department