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Author: Pushan Sharma Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
In this time of severe climate change, there is an increasing need for sophisticated simulation tools to facilitate more efficient fossil-fuel based combustion devices with low pollutant and greenhouse gas emissions. In particular, to simulate a turbulent reacting flow, a proper prediction of the interactions between turbulence and chemistry is extremely important. Probability density function (PDF) methods have been shown to capture this strong turbulence chemistry interaction accurately. However, one of the biggest disadvantages of PDF methods is its significantly higher computational cost of solving the chemistry in its exact form compared to other simpler methods, such as flamelet-based models. This necessitates the development of strategies to reduce the cost of PDF type approaches without losing the level of accuracy. Two different categories of techniques to accelerate the process are explored in this thesis. The use of analytical Jacobian is observed to be a promising step to accelerate the chemistry source term integration compared to using numerical Jacobian. Here, a generalized projection-based analytical Jacobian framework is provided that considers all species mass fractions and temperature in the state vector while satisfying the mass conservation constraint consistently. The use of a projection matrix with the analytical Jacobian ensures that the mass fraction vector never goes off its realizable simplex, defined by the constraint, at any time step. This approach provides an accurate solution with different types of solvers, and also predicts the spectral properties of the corresponding dynamical system within round-off errors. Next, the algorithm for generating the analytical Jacobian is combined with a dimension reduction technique, the quasi-steady species (QSS) assumption. An automated algorithm package is developed, which provides the analytical expression of the Jacobian with QSS species, properly integrating all the additional derivatives corresponding to the QSS-derived algebraic expressions, and can be readily implemented in any high-fidelity turbulent simulation. Combining these two techniques (analytical Jacobian and QSS) has shown a significant reduction in the computational cost of a partially stirred reactor (PaSR) simulation. Adaptive chemistry approaches, which tailor the fidelity and size of the kinetic models used for reaction integration to the local flame conditions, have reduced the cost of PDF-type methods due to their ability to accurately describe the relevant combustion kinetics with significantly fewer variables and equations. In this work, two new adaptive chemistry algorithms are developed. The first addresses a key challenge of efficiently capturing the secondary chemistry pathways, such as pollutant formation, in an existing pre-partitioned adaptive chemistry (PPAC) approach. This new algorithm, PPAC-Additive, decouples the secondary chemistry from primary chemistry pathways (fuel oxidation), thus developing smaller reduced kinetic models compared to PPAC. In PPAC-Additive, the reduced models are generated first for main oxidation targets only, and then the important secondary pathways, demonstrated with NOx prediction, are dealt with afterwards in a separate stage. Both PPAC and PPAC-Additive generate the reduced models based on a sample set of compositions in an offline stage, which are then used adaptively during the simulation of interest. In contrast to the current adaptive frameworks, which require extensive pre-processing analysis and assumption, the second algorithm, dynamically partitioned adaptive chemistry (DPAC), is a completely stand-alone adaptive approach with limited need for user input. DPAC generates the reduced models during the adaptive simulation based on the encountered compositions at runtime. DPAC updates the reduced kinetic models continuously as the flame and its compositions evolve in time, making it more flexible and efficient than other existing adaptive ...
Author: Pushan Sharma Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
In this time of severe climate change, there is an increasing need for sophisticated simulation tools to facilitate more efficient fossil-fuel based combustion devices with low pollutant and greenhouse gas emissions. In particular, to simulate a turbulent reacting flow, a proper prediction of the interactions between turbulence and chemistry is extremely important. Probability density function (PDF) methods have been shown to capture this strong turbulence chemistry interaction accurately. However, one of the biggest disadvantages of PDF methods is its significantly higher computational cost of solving the chemistry in its exact form compared to other simpler methods, such as flamelet-based models. This necessitates the development of strategies to reduce the cost of PDF type approaches without losing the level of accuracy. Two different categories of techniques to accelerate the process are explored in this thesis. The use of analytical Jacobian is observed to be a promising step to accelerate the chemistry source term integration compared to using numerical Jacobian. Here, a generalized projection-based analytical Jacobian framework is provided that considers all species mass fractions and temperature in the state vector while satisfying the mass conservation constraint consistently. The use of a projection matrix with the analytical Jacobian ensures that the mass fraction vector never goes off its realizable simplex, defined by the constraint, at any time step. This approach provides an accurate solution with different types of solvers, and also predicts the spectral properties of the corresponding dynamical system within round-off errors. Next, the algorithm for generating the analytical Jacobian is combined with a dimension reduction technique, the quasi-steady species (QSS) assumption. An automated algorithm package is developed, which provides the analytical expression of the Jacobian with QSS species, properly integrating all the additional derivatives corresponding to the QSS-derived algebraic expressions, and can be readily implemented in any high-fidelity turbulent simulation. Combining these two techniques (analytical Jacobian and QSS) has shown a significant reduction in the computational cost of a partially stirred reactor (PaSR) simulation. Adaptive chemistry approaches, which tailor the fidelity and size of the kinetic models used for reaction integration to the local flame conditions, have reduced the cost of PDF-type methods due to their ability to accurately describe the relevant combustion kinetics with significantly fewer variables and equations. In this work, two new adaptive chemistry algorithms are developed. The first addresses a key challenge of efficiently capturing the secondary chemistry pathways, such as pollutant formation, in an existing pre-partitioned adaptive chemistry (PPAC) approach. This new algorithm, PPAC-Additive, decouples the secondary chemistry from primary chemistry pathways (fuel oxidation), thus developing smaller reduced kinetic models compared to PPAC. In PPAC-Additive, the reduced models are generated first for main oxidation targets only, and then the important secondary pathways, demonstrated with NOx prediction, are dealt with afterwards in a separate stage. Both PPAC and PPAC-Additive generate the reduced models based on a sample set of compositions in an offline stage, which are then used adaptively during the simulation of interest. In contrast to the current adaptive frameworks, which require extensive pre-processing analysis and assumption, the second algorithm, dynamically partitioned adaptive chemistry (DPAC), is a completely stand-alone adaptive approach with limited need for user input. DPAC generates the reduced models during the adaptive simulation based on the encountered compositions at runtime. DPAC updates the reduced kinetic models continuously as the flame and its compositions evolve in time, making it more flexible and efficient than other existing adaptive ...
Author: Ashish Shireeshkumar Newale Publisher: ISBN: Category : Languages : en Pages : 191
Book Description
There is a time critical need for design of fossil fuel based energy conversion devices that attain the dual and usually competing objectives of high efficiency and low pollutant emissions. The design of such devices can be informed by, and in certain instances derived from predictive computations. A crucial component of reacting flow simulations that are predictive is the turbulent combustion model. Probability density function (PDF) methods have been shown to accurately capture flames with strong turbulence chemistry interactions. However, PDF methods are known to be more computationally intensive than simpler topology based approaches such as steady laminar flamelet models. The recently proposed pre-partitioned adaptive chemistry (PPAC) methodology mitigates the cost of using particle PDF methods while maintaining their accuracy. PPAC generates a set of reduced models in an offline preprocessing stage, which are then dynamically utilized at runtime for integrating particle compositions. In the first part of this work, PPAC is augmented by combining it with complementary dimension reduction (rate-controlled constrained equilibrium (RCCE)) and storage retrieval methods (in-situ adaptive tabulation (ISAT)). The combined PPAC-RCCE-ISAT method is shown to outperform standalone PPAC by avoiding redundant direct integrations leading to a significant reduction in the CPU cost, and achieving a sizable reduction in the memory requirement by retaining fewer variables at runtime. Though PPAC has been developed for reducing the computational cost of particle PDF computations, it had previously been tested only in a partially stirred reactor (PaSR). Consequently, an integrated PPAC (-ISAT) particle PDF solver is developed as part of the current work. A detailed assessment of PPAC and PPAC-ISAT in LES/PDF simulations of turbulent combustion is completed using the developed solver. For a large-scale simulation of Sandia flame D, the coupled PPAC-ISAT particle PDF solver is shown to reduce the average wall clock time of a standalone ISAT implementation using the detailed mechanism by 39%, with a minimal loss of accuracy. A key assumption made in the PPAC framework is that the compositions used in the offline preprocessing stage are representative of those encountered at runtime. Hence, the efficient generation of a representative database is crucial to the success of PPAC. The suitability of existing canonical 0D-1D reactors is examined for this purpose. Specifically, compositions obtained from these canonical reactors are compared to the compositions extracted from a variety of direct numerical simulations using an ISAT based approach. We show that the compositions obtained from 1D counterflow flames and PaSR are representative of a significant fraction of the compositions encountered in turbulent combustion simulations. To directly quantify the impact of using databases generated from canonical 0D-1D reactors, we use the coupled PPAC-ISAT particle PDF solver for performing LES/PDF simulations of Sandia flame D. We explore two databases: a first one generated using compositions extracted from 1D counterflow flames, and a second one using compositions from a PaSR. We show that the use of these efficiently generated databases leads to results that are comparable to the case where the database is comprised of compositions extracted from the LES/PDF simulation itself. Finally, avenues for further research that can significantly improve the utility of PPAC for enabling computationally-efficient and accurate particle PDF computations are identified.
Author: Tarek Echekki Publisher: Springer ISBN: 9789400734777 Category : Technology & Engineering Languages : en Pages : 0
Book Description
Turbulent combustion sits at the interface of two important nonlinear, multiscale phenomena: chemistry and turbulence. Its study is extremely timely in view of the need to develop new combustion technologies in order to address challenges associated with climate change, energy source uncertainty, and air pollution. Despite the fact that modeling of turbulent combustion is a subject that has been researched for a number of years, its complexity implies that key issues are still eluding, and a theoretical description that is accurate enough to make turbulent combustion models rigorous and quantitative for industrial use is still lacking. In this book, prominent experts review most of the available approaches in modeling turbulent combustion, with particular focus on the exploding increase in computational resources that has allowed the simulation of increasingly detailed phenomena. The relevant algorithms are presented, the theoretical methods are explained, and various application examples are given. The book is intended for a relatively broad audience, including seasoned researchers and graduate students in engineering, applied mathematics and computational science, engine designers and computational fluid dynamics (CFD) practitioners, scientists at funding agencies, and anyone wishing to understand the state-of-the-art and the future directions of this scientifically challenging and practically important field.
Author: Kenneth Kuan-yun Kuo Publisher: John Wiley & Sons ISBN: 0470226226 Category : Science Languages : en Pages : 914
Book Description
Detailed coverage of advanced combustion topics from the author of Principles of combustion, Second Edition Turbulence, turbulent combustion, and multiphase reacting flows have become major research topics in recent decades due to their application across diverse fields, including energy, environment, propulsion, transportation, industrial safety, and nanotechnology. Most of the knowledge accumulated from this research has never been published in book form—until now. Fundamentals of Turbulent and Multiphase Combustion presents up-to-date, integrated coverage of the fundamentals of turbulence, combustion, and multiphase phenomena along with useful experimental techniques, including non-intrusive, laser-based measurement techniques, providing a firm background in both contemporary and classical approaches. Beginning with two full chapters on laminar premixed and non-premixed flames, this book takes a multiphase approach, beginning with more common topics and moving on to higher-level applications. In addition, Fundamentals of Turbulent and Multiphase Combustion: Addresses seven basic topical areas in combustion and multiphase flows, including laminar premixed and non-premixed flames, theory of turbulence, turbulent premixed and non-premixed flames, and multiphase flows Covers spray atomization and combustion, solid-propellant combustion, homogeneous propellants, nitramines, reacting boundary-layer flows, single energetic particle combustion, and granular bed combustion Provides experimental setups and results whenever appropriate Supported with a large number of examples and problems as well as a solutions manual, Fundamentals of Turbulent and Multiphase Combustion is an important resource for professional engineers and researchers as well as graduate students in mechanical, chemical, and aerospace engineering.
Author: N. Swaminathan Publisher: Cambridge University Press ISBN: 1108497969 Category : Science Languages : en Pages : 485
Book Description
Explore a thorough overview of the current knowledge, developments and outstanding challenges in turbulent combustion and application.
Author: Varun Hiremath Publisher: ISBN: Category : Languages : en Pages : 566
Book Description
A major challenge in the numerical simulations of turbulent reacting flows involving large numbers of chemical species and reactions is the accurate and computationally-efficient representation of combustion chemistry. Recent advances on the experimental and theoretical fronts of the study of real fuel chemistry have led to more accurate chemical mechanisms of real fuels involving hundreds to thousands of species and thousands of reactions. However, the direct use of such detailed chemistry in large-scale calculations of turbulent reacting flows still remains computationally prohibitive. In our work, we focus on the combined Large-Eddy Simulation (LES)/Probability Density Function (PDF) computations of turbulent reacting flows, in which the thermochemical composition of the fluid is represented by a large number of particles. To reduce the cost of chemistry calculations in large-scale LES/PDF computations, we have developed a combined dimension reduction and tabulation approach in which the chemistry is represented accurately and efficiently in terms of a reduced number of "represented species". In this combined approach, the dimension reduction of combustion chemistry is performed using the Rate-Controlled Constrained-Equilibrium (RCCE) method, followed by tabulation using the In Situ Adaptive Tabulation (ISAT) algorithm. An automated Greedy Algorithm with Local Improvement (GALI) has been developed for selecting good rep- resented species for use in this approach. In addition, we have developed a Partitioned Uniform Random (P-URAN) parallel strategy for the efficient parallel implementation of chemistry in large-scale LES/PDF simulations on multiple cores. This strategy has been tested by performing full-scale LES/PDF simulations of the Sandia Flame D turbulent jet flame on up to 9,216 cores and it is found to achieve good scaling. In this work (1) we describe in detail the implementation of ISAT/RCCE/GALI and the P-URAN parallel strategy; (2) we show that the combined ISAT/RCCE/GALI yields orders of magnitude speed-up with very good error control; (3) we demonstrate that our implementation of RCCE is an accurate, efficient and robust implementation; (4) we show that the P-URAN parallel strategy achieves over 85% relative weak scaling efficiency and around 60% relative strong scaling efficiency on up to 9,216 cores; (5) we show that the combined ISAT/RCCE methodology with P-URAN significantly reduces the simulation time; and (6) a combination of ISAT/RCCE and PURAN algorithms enables us to perform accurate and computationally-efficient large-scale LES/PDF simulations with real fuel chemistry involving hundreds of chemical species.
Author: Publisher: ISBN: Category : Languages : en Pages : 144
Book Description
The overall objective of the research project was to develop, test and demonstrate a combined methodology for modelling turbulent combustion. The method was based on the solution by a particle/Monte Carlo method-of a modelled transport equation for the joint probability density function (PDF) of velocity, turbulence frequency, and thermochemical composition. New contributions were made to several aspects of the method. An improved turbulent mixing model (EMST) was developed and demonstrated in turbulent flames. A new model for turbulence frequency, and a wavevector model that is exact for rapid distortions was developed. The PDF methodology was also extended for incorporation in large eddy simulations. Overall, the PDF method was substantially advanced and demonstrated to be an effective approach for calculating the turbulent reactive flows encountered in propulsion devices.
Author: Andrei Lipatnikov Publisher: Mdpi AG ISBN: 9783039365456 Category : Technology & Engineering Languages : en Pages : 142
Book Description
Turbulent burning of gaseous fuels is widely used for energy conversion in stationary power generation, e.g., gas turbines, land transportation, piston engines, and aviation, and aero-engine afterburners. Nevertheless, our fundamental understanding of turbulent combustion is still limited, because it is a highly non-linear and multiscale process that involves various local phenomena and thousands (e.g., for gasoline-air mixtures) of chemical reactions between hundreds of species, including several reactions that control emissions from flames. Therefore, there is a strong need for elaborating high fidelity, advanced numerical models, and methods that will catch the governing physical mechanisms of flame-turbulence interaction and, consequently, will make turbulent combustion computations an efficient predictive tool for applied research and, in particular, for development of a new generation of ultra-clean and highly efficient internal combustion engines that will allow society to properly respond to current environmental and efficiency challenges. Accordingly, papers published in this Special Issue (i) contribute to our fundamental understanding of flame-turbulence interaction by analyzing results of unsteady multi-dimensional numerical simulations and (ii) develop and validate high-fidelity models and efficient numerical methods for computational fluid Dynamics research into turbulent combustion in laboratory burners and engines.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The TSTC project is a multi-university collaborative effort to develop a high-fidelity turbulent reacting flow simulation capability utilizing terascale, massively parallel computer technology. The main paradigm of our approach is direct numerical simulation (DNS) featuring highest temporal and spatial accuracy, allowing quantitative observations of the fine-scale physics found in turbulent reacting flows as well as providing a useful tool for development of sub-models needed in device-level simulations. The code named S3D, developed and shared with Chen and coworkers at Sandia National Laboratories, has been enhanced with new numerical algorithms and physical models to provide predictive capabilities for spray dynamics, combustion, and pollutant formation processes in turbulent combustion. Major accomplishments include improved characteristic boundary conditions, fundamental studies of auto-ignition in turbulent stratified reactant mixtures, flame-wall interaction, and turbulent flame extinction by water spray. The overarching scientific issue in our recent investigations is to characterize criticality phenomena (ignition/extinction) in turbulent combustion, thereby developing unified criteria to identify ignition and extinction conditions. The computational development under TSTC has enabled the recent large-scale 3D turbulent combustion simulations conducted at Sandia National Laboratories.
Author: Pushan Sharma
Author: Pushan Sharma
Author: Ashish Shireeshkumar Newale
Author: Tarek Echekki
Author: Kenneth Kuan-yun Kuo
Author: N. Swaminathan
Author: Varun Hiremath
Author: 
Author: Andrei Lipatnikov
Author: 
Author: Anja Ketelheun