Tabulation Process

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Matthew J. Dunn - One of the best experts on this subject based on the ideXlab platform.

  • Large Eddy Simulation of a premixed jet flame stabilized by a vitiated co-flow: Evaluation of auto-ignition tabulated chemistry
    Combustion and Flame, 2013
    Co-Authors: Christophe Duwig, Matthew J. Dunn
    Abstract:

    Abstract A Tabulation technique assuming an auto-ignition dominated reaction pathway for highly turbulent premixed combustion is presented, implemented in an LES framework and evaluated. The Tabulation method enables the reduction of the chemical system dimension to two scalars, allowing a computationally efficient model implementation, yet still retaining a sufficiently accurate representation of the chemical kinetics. The sensitivity of the LES model to the grid, inflow conditions, subgrid model, Tabulation method assumptions and the chemical mechanism used in the Tabulation Process is evaluated with reference to detailed experimental measurements. The particular chemical mechanism utilized for the Tabulation is shown to have a significant effect on the CO and OH concentrations, whilst only a small influence on the temperature and mixing fields. Comparisons with laminar flame based Tabulation explain the misprediction of CO concentration. However, both the auto-ignition and laminar flame based Tabulations fail to capture the OH concentration. The ability of the two Tabulation techniques to capture the non-flamelet structure is discussed and the predictive capability of the two approaches is established. The general utility of a global Karlovitz number for describing the combustion regime and hence the selection of an applicable combustion model is brought into question considering that the variation of the local Karlovitz number in the simulations varies by up to 2 orders of magnitude, indicating a broad range of accessed flame structures.

Sibendu Som - One of the best experts on this subject based on the ideXlab platform.

  • Implementation of Detailed Chemistry Mechanisms in Engine Simulations
    Journal of Engineering for Gas Turbines and Power, 2018
    Co-Authors: Prithwish Kundu, Muhsin M. Ameen, Umesh Unnikrishnan, Sibendu Som
    Abstract:

    The stiffness of large chemistry mechanisms has been proved to be a major hurdle toward predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increases super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed tabulated flamelet model (TFM) framework for nonpremixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with variable coefficient ordinary differential equation (ODE) solver (VODE) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the Livermore solver for ODEs in sparse form (LSODES) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional variable coefficient ODE (VODE) solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2755 species and 11,173 reactions. The engine combustion network (ECN) spray A experiments, which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 ×106 peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths (LOLs). Qualitative results from the simulations were compared against experimental OH and CH2O planar laser-induced fluorescence (PLIF) data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the Tabulation Process and a small increase in the 3D simulation cost.

  • Implementation of Detailed Chemistry Mechanisms in Engine Simulations
    Volume 2: Emissions Control Systems; Instrumentation Controls and Hybrids; Numerical Simulation; Engine Design and Mechanical Development, 2017
    Co-Authors: Prithwish Kundu, Muhsin M. Ameen, Umesh Unnikrishnan, Sibendu Som
    Abstract:

    The stiffness of large chemistry mechanisms has been proved to be a major hurdle towards predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increase super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed Tabulated Flamelet Model (TFM) framework for non-premixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with VODE (Variable coefficient ODE solver) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the LSODES (Livermore Solver for ODEs in Sparse form) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional VODE solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2,755 species and 11,173 reactions. The Engine Combustion Network (ECN) Spray A experiments which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 million peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths. Qualitative results from the simulations were compared against experimental OH and CH2O PLIF data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the Tabulation Process and a small increase in the 3D simulation cost.

Jonathan Mellon - One of the best experts on this subject based on the ideXlab platform.

  • A Get-Out-the-Vote Experiment on the World’s Largest Participatory Budgeting Vote in Brazil
    British Journal of Political Science, 2017
    Co-Authors: Tiago Peixoto, Fredrik M. Sjoberg, Jonathan Mellon
    Abstract:

    Does non-partisan voter mobilization affect the popular vote? We use vote records from a state-level participatory budgeting vote in Brazil– the world’s largest –to assess the impact of voter mobilization messaging on turnout and support for public investments. The government provided records as to how each ballot was cast and designed the Tabulation Process so that votes could be matched to treatment assignment without compromising the secrecy of the ballot. Citizens (n=43,384) were randomly assigned to receive non-partisan email and text messages designed to encourage voting. We document an impressive 4.7 percentage point increase in online voting in our treatment group. However, we found no effect of messaging on vote choice; voters in the treatment and control groups shared the same sectoral preferences and showed no difference in the average cost of public investment projects they supported. These results suggest non-partisan Get Out the Vote campaigns can increase citizen participation without skewing the outcome.

Christophe Duwig - One of the best experts on this subject based on the ideXlab platform.

  • Large Eddy Simulation of a premixed jet flame stabilized by a vitiated co-flow: Evaluation of auto-ignition tabulated chemistry
    Combustion and Flame, 2013
    Co-Authors: Christophe Duwig, Matthew J. Dunn
    Abstract:

    Abstract A Tabulation technique assuming an auto-ignition dominated reaction pathway for highly turbulent premixed combustion is presented, implemented in an LES framework and evaluated. The Tabulation method enables the reduction of the chemical system dimension to two scalars, allowing a computationally efficient model implementation, yet still retaining a sufficiently accurate representation of the chemical kinetics. The sensitivity of the LES model to the grid, inflow conditions, subgrid model, Tabulation method assumptions and the chemical mechanism used in the Tabulation Process is evaluated with reference to detailed experimental measurements. The particular chemical mechanism utilized for the Tabulation is shown to have a significant effect on the CO and OH concentrations, whilst only a small influence on the temperature and mixing fields. Comparisons with laminar flame based Tabulation explain the misprediction of CO concentration. However, both the auto-ignition and laminar flame based Tabulations fail to capture the OH concentration. The ability of the two Tabulation techniques to capture the non-flamelet structure is discussed and the predictive capability of the two approaches is established. The general utility of a global Karlovitz number for describing the combustion regime and hence the selection of an applicable combustion model is brought into question considering that the variation of the local Karlovitz number in the simulations varies by up to 2 orders of magnitude, indicating a broad range of accessed flame structures.

Prithwish Kundu - One of the best experts on this subject based on the ideXlab platform.

  • Implementation of Detailed Chemistry Mechanisms in Engine Simulations
    Journal of Engineering for Gas Turbines and Power, 2018
    Co-Authors: Prithwish Kundu, Muhsin M. Ameen, Umesh Unnikrishnan, Sibendu Som
    Abstract:

    The stiffness of large chemistry mechanisms has been proved to be a major hurdle toward predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increases super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed tabulated flamelet model (TFM) framework for nonpremixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with variable coefficient ordinary differential equation (ODE) solver (VODE) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the Livermore solver for ODEs in sparse form (LSODES) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional variable coefficient ODE (VODE) solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2755 species and 11,173 reactions. The engine combustion network (ECN) spray A experiments, which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 ×106 peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths (LOLs). Qualitative results from the simulations were compared against experimental OH and CH2O planar laser-induced fluorescence (PLIF) data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the Tabulation Process and a small increase in the 3D simulation cost.

  • Implementation of Detailed Chemistry Mechanisms in Engine Simulations
    Volume 2: Emissions Control Systems; Instrumentation Controls and Hybrids; Numerical Simulation; Engine Design and Mechanical Development, 2017
    Co-Authors: Prithwish Kundu, Muhsin M. Ameen, Umesh Unnikrishnan, Sibendu Som
    Abstract:

    The stiffness of large chemistry mechanisms has been proved to be a major hurdle towards predictive engine simulations. As a result, detailed chemistry mechanisms with a few thousand species need to be reduced based on target conditions so that they can be accommodated within the available computational resources. The computational cost of simulations typically increase super-linearly with the number of species and reactions. This work aims to bring detailed chemistry mechanisms within the realm of engine simulations by coupling the framework of unsteady flamelets and fast chemistry solvers. A previously developed Tabulated Flamelet Model (TFM) framework for non-premixed combustion was used in this study. The flamelet solver consists of the traditional operator-splitting scheme with VODE (Variable coefficient ODE solver) and a numerical Jacobian for solving the chemistry. In order to use detailed mechanisms with thousands of species, a new framework with the LSODES (Livermore Solver for ODEs in Sparse form) chemistry solver and an analytical Jacobian was implemented in this work. Results from 1D simulations show that with the new framework, the computational cost is linearly proportional to the number of species in a given chemistry mechanism. As a result, the new framework is 2–3 orders of magnitude faster than the conventional VODE solver for large chemistry mechanisms. This new framework was used to generate unsteady flamelet libraries for n-dodecane using a detailed chemistry mechanism with 2,755 species and 11,173 reactions. The Engine Combustion Network (ECN) Spray A experiments which consist of an igniting n-dodecane spray in turbulent, high-pressure engine conditions are simulated using large eddy simulations (LES) coupled with detailed mechanisms. A grid with 0.06 mm minimum cell size and 22 million peak cell count was implemented. The framework is validated across a range of ambient temperatures against ignition delay and liftoff lengths. Qualitative results from the simulations were compared against experimental OH and CH2O PLIF data. The models are able to capture the spatial and temporal trends in species compared to those observed in the experiments. Quantitative and qualitative comparisons between the predictions of the reduced and detailed mechanisms are presented in detail. The main goal of this study is to demonstrate that detailed reaction mechanisms (∼1000 species) can now be used in engine simulations with a linear increase in computation cost with number of species during the Tabulation Process and a small increase in the 3D simulation cost.