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Papers by obulesu chatakonda

Research paper thumbnail of A petascale direct numerical simulation study of the modelling of flame wrinkling for large-eddy simulations in intense turbulence

Combustion and Flame, Aug 1, 2012

ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combus... more ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combustion with detailed chemistry in a temporally evolving slot-jet configuration is presented as a database for the development and validation of models for premixed turbulent combustion. The jet Reynolds number is 10,000, requiring grid numbers up to nearly seven billion, which was achieved by computation on 120,000 processor cores. In contrast to many prior DNS studies, a mean shear exists that drives strong turbulent mixing within the flame structure. Three cases are simulated with different Damköhler numbers, while Reynolds number is held fixed. Basic statistics are presented showing that integrated burning rates up to approximately six times the laminar burning rate are obtained. It is shown that increased flame surface area accounts for most of the enhanced burning while increases in the burning rate per unit area also play an important contribution.The database is then used to assess a new model of flame wrinkling intended for large-eddy simulations (LES). The approach draws on concepts from fractal geometry, requiring the modelling of an inner cut-off scale representing the smallest scale of flame wrinkling, and the fractal dimension controlling the resolution dependence of the unresolved flame surface area. In contrast to previous modelling, it is argued that the inner cut-off should be filter-size invariant in an inertial range. Then, dimensional and physical reasoning together with Damköhler’s limiting scaling laws for the turbulent flame speed are used to infer the cut-off and fractal dimension in limiting regimes. Two methods of determining the fractal dimension are proposed: a static, algebraic expression or a dynamic approach exploiting a Germano-type identity. Finally the model is compared against the DNS in a priori tests and is found to give excellent results, quantitatively capturing the trends with time, space, filter size and Damköhler number.

Research paper thumbnail of Large Eddy simulations of premixed turbulent combustion

In the past two decades, Large-Eddy Simulation (LES) has become well established for modelling no... more In the past two decades, Large-Eddy Simulation (LES) has become well established for modelling non-reacting flows. However, LES is still undergoing significant development for reacting flows. The mostchallenging topic in LES of combusting flows is modelling the reaction rate. To this end, several models have been proposed in the literature. Many of the models proposed so far are limited to corrugated flame (CF) regime. However, in many premixed combustion applications both CF and thin reaction zone (TRZ) regimes exist. There is, therefore, a need for accurate and robust physical modelling of the reaction rate across different regimes of premixed flames. In this thesis, a new flame wrinkling model is proposed based on fractal geometry concept requiring the modelling of an inner cut-off scale and fractal dimension. Damk¨ohlers limiting scaling laws are usedto infer the cut-off and fractal dimension in limiting regimes. The assumptions made to obtain the fractal dimension in the propos...

Research paper thumbnail of Direct numerical simulation of a partially premixed turbulent, lifted flame

Research paper thumbnail of A petascale direct numerical simulation study of the modelling of flame wrinkling for large-eddy simulations in intense turbulence

Combustion and Flame, 2012

ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combus... more ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combustion with detailed chemistry in a temporally evolving slot-jet configuration is presented as a database for the development and validation of models for premixed turbulent combustion. The jet Reynolds number is 10,000, requiring grid numbers up to nearly seven billion, which was achieved by computation on 120,000 processor cores. In contrast to many prior DNS studies, a mean shear exists that drives strong turbulent mixing within the flame structure. Three cases are simulated with different Damköhler numbers, while Reynolds number is held fixed. Basic statistics are presented showing that integrated burning rates up to approximately six times the laminar burning rate are obtained. It is shown that increased flame surface area accounts for most of the enhanced burning while increases in the burning rate per unit area also play an important contribution.The database is then used to assess a new model of flame wrinkling intended for large-eddy simulations (LES). The approach draws on concepts from fractal geometry, requiring the modelling of an inner cut-off scale representing the smallest scale of flame wrinkling, and the fractal dimension controlling the resolution dependence of the unresolved flame surface area. In contrast to previous modelling, it is argued that the inner cut-off should be filter-size invariant in an inertial range. Then, dimensional and physical reasoning together with Damköhler’s limiting scaling laws for the turbulent flame speed are used to infer the cut-off and fractal dimension in limiting regimes. Two methods of determining the fractal dimension are proposed: a static, algebraic expression or a dynamic approach exploiting a Germano-type identity. Finally the model is compared against the DNS in a priori tests and is found to give excellent results, quantitatively capturing the trends with time, space, filter size and Damköhler number.

Research paper thumbnail of On the fractal characteristics of low Damköhler number flames

Combustion and Flame, 2013

ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used t... more ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used to help develop turbulent combustion models. Here, direct numerical simulations of low Damkohler number flames are used to analyse the fractal nature of the flames. Two sets of data are considered: (i) thermochemical hydrogen-air turbulent premixed plane-jet flames with detailed chemistry and (ii) thermonuclear flames in type la supernovae. A three-dimensional box counting method is used to investigate fractal dimension of the flame surface, characterising the self similarity of flame fronts. In the premixed flames, the fractal dimension is found to vary in time between 2.1 and 2.7. The supernovae flames in distributed combustion regimes yield fractal dimension about 2.7. The results for the maximum fractal dimensions are higher than previously reported. They are explained theoretically by a Reynolds number similarity argument which posits that the high Reynolds number, low Damkohler number limiting value of the fractal dimension is 8/3. Also tested is Mandelbrot's fractal additive law which relates the fractal dimension determined in two dimensions, which is typical of experimental measurements, to that in three dimensions. The comparison of the fractal dimension in both two-dimensional and three-dimensional spaces supports the additive law, even though the flames considered do not formally satisfy isotropy. Finally, the inner-cut off is extracted from the hydrogen flames and found to be consistent in order of magnitude with Kolmogorov scaling.

Research paper thumbnail of A posteriori large-eddy simulations of a turbulent premixed flame in the thin reaction zones regime

Large-eddy simulations (LES) have been successfully applied to premixed turbulent flames in the f... more Large-eddy simulations (LES) have been successfully applied to premixed turbulent flames in the flamelet regime. However, in the context of LES, comparatively little effort has focused on modelling of premixed flames in regimes of combustion in which the small scale eddies can penetrate the flame, the most important of which is the so-called thin-reaction zones (TRZ) regime. In this work, a posteriori LES of a turbulent premixed, methaneair slot-jet are performed using strained and unstrained premixed flamelet ...

Research paper thumbnail of On the fractal characteristics of low Damköhler number flames

Combustion and Flame, Nov 1, 2013

ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used t... more ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used to help develop turbulent combustion models. Here, direct numerical simulations of low Damkohler number flames are used to analyse the fractal nature of the flames. Two sets of data are considered: (i) thermochemical hydrogen-air turbulent premixed plane-jet flames with detailed chemistry and (ii) thermonuclear flames in type la supernovae. A three-dimensional box counting method is used to investigate fractal dimension of the flame surface, characterising the self similarity of flame fronts. In the premixed flames, the fractal dimension is found to vary in time between 2.1 and 2.7. The supernovae flames in distributed combustion regimes yield fractal dimension about 2.7. The results for the maximum fractal dimensions are higher than previously reported. They are explained theoretically by a Reynolds number similarity argument which posits that the high Reynolds number, low Damkohler number limiting value of the fractal dimension is 8/3. Also tested is Mandelbrot's fractal additive law which relates the fractal dimension determined in two dimensions, which is typical of experimental measurements, to that in three dimensions. The comparison of the fractal dimension in both two-dimensional and three-dimensional spaces supports the additive law, even though the flames considered do not formally satisfy isotropy. Finally, the inner-cut off is extracted from the hydrogen flames and found to be consistent in order of magnitude with Kolmogorov scaling.

Research paper thumbnail of Effect of Oxygen Enrichment on Methane Ignition

Social Science Research Network, 2023

Research paper thumbnail of An Updated Functional-Group-Based Approach to Modeling the Vacuum Residue Oil Gasification Kinetics

Research paper thumbnail of Effect of Water Vapor on the Oxidation of Heavy Fuel and Vacuum Residue Oil in a Tga

Research paper thumbnail of An Updated Functional-Group-Based Approach to Modeling the Vacuum Residue Oil Gasification Kinetics

Research paper thumbnail of Effect of pressure and CO2 dilution on soot formation in laminar inverse coflow flame at conditions close to autothermal reforming

Research paper thumbnail of Effect of Oxygen Enrichment on Methane Ignition

Research paper thumbnail of TG-DSC and TG-FTIR analysis of heavy fuel oil and vacuum residual oil pyrolysis and combustion: characterization, kinetics, and evolved gas analysis

Journal of Thermal Analysis and Calorimetry

Research paper thumbnail of Heavy-Oil Surrogate Formulation Based on Ft-Icr Ms Analysis

SSRN Electronic Journal

Generally, surrogate molecules are used to represent complex oil mixtures for property prediction... more Generally, surrogate molecules are used to represent complex oil mixtures for property predictions and kinetic model development. The aim of a surrogate formulation is to represent the chemical and physical properties of a complex oil matrix with a single molecule or only a few species. The chemical kinetic model of the proposed surrogate can be used to simulate oil behavior in different scenarios such as pyrolysis and oxidation. However, the surrogate formulation of heavy oils requires a characterization using many chemical analytical techniques, which are expensive, time-consuming, and hard to interpret. This study presents a new heavy oil surrogate formulation methodology based only on high-resolution mass spectrometry. The methodology was used to

Research paper thumbnail of Soot production in high pressure inverse diffusion flames with enriched oxygen in the oxidizer stream

Research paper thumbnail of The effect of preheating temperature on PAH/soot formation in methane/air co-flow flames at elevated pressure

Research paper thumbnail of 18th Australasian Fluid Mechanics Conference

A posteriori large-eddy simulations of a turbulent premixed flame in the thin reaction zones regime

Research paper thumbnail of A petascale direct numerical simulation study of the modelling of flame wrinkling for large-eddy simulations in intense turbulence

Combustion and Flame, Aug 1, 2012

ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combus... more ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combustion with detailed chemistry in a temporally evolving slot-jet configuration is presented as a database for the development and validation of models for premixed turbulent combustion. The jet Reynolds number is 10,000, requiring grid numbers up to nearly seven billion, which was achieved by computation on 120,000 processor cores. In contrast to many prior DNS studies, a mean shear exists that drives strong turbulent mixing within the flame structure. Three cases are simulated with different Damköhler numbers, while Reynolds number is held fixed. Basic statistics are presented showing that integrated burning rates up to approximately six times the laminar burning rate are obtained. It is shown that increased flame surface area accounts for most of the enhanced burning while increases in the burning rate per unit area also play an important contribution.The database is then used to assess a new model of flame wrinkling intended for large-eddy simulations (LES). The approach draws on concepts from fractal geometry, requiring the modelling of an inner cut-off scale representing the smallest scale of flame wrinkling, and the fractal dimension controlling the resolution dependence of the unresolved flame surface area. In contrast to previous modelling, it is argued that the inner cut-off should be filter-size invariant in an inertial range. Then, dimensional and physical reasoning together with Damköhler’s limiting scaling laws for the turbulent flame speed are used to infer the cut-off and fractal dimension in limiting regimes. Two methods of determining the fractal dimension are proposed: a static, algebraic expression or a dynamic approach exploiting a Germano-type identity. Finally the model is compared against the DNS in a priori tests and is found to give excellent results, quantitatively capturing the trends with time, space, filter size and Damköhler number.

Research paper thumbnail of Large Eddy simulations of premixed turbulent combustion

In the past two decades, Large-Eddy Simulation (LES) has become well established for modelling no... more In the past two decades, Large-Eddy Simulation (LES) has become well established for modelling non-reacting flows. However, LES is still undergoing significant development for reacting flows. The mostchallenging topic in LES of combusting flows is modelling the reaction rate. To this end, several models have been proposed in the literature. Many of the models proposed so far are limited to corrugated flame (CF) regime. However, in many premixed combustion applications both CF and thin reaction zone (TRZ) regimes exist. There is, therefore, a need for accurate and robust physical modelling of the reaction rate across different regimes of premixed flames. In this thesis, a new flame wrinkling model is proposed based on fractal geometry concept requiring the modelling of an inner cut-off scale and fractal dimension. Damk¨ohlers limiting scaling laws are usedto infer the cut-off and fractal dimension in limiting regimes. The assumptions made to obtain the fractal dimension in the propos...

Research paper thumbnail of Direct numerical simulation of a partially premixed turbulent, lifted flame

Research paper thumbnail of A petascale direct numerical simulation study of the modelling of flame wrinkling for large-eddy simulations in intense turbulence

Combustion and Flame, 2012

ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combus... more ABSTRACT A new set of petascale direct numerical simulations (DNS) modelling lean hydrogen combustion with detailed chemistry in a temporally evolving slot-jet configuration is presented as a database for the development and validation of models for premixed turbulent combustion. The jet Reynolds number is 10,000, requiring grid numbers up to nearly seven billion, which was achieved by computation on 120,000 processor cores. In contrast to many prior DNS studies, a mean shear exists that drives strong turbulent mixing within the flame structure. Three cases are simulated with different Damköhler numbers, while Reynolds number is held fixed. Basic statistics are presented showing that integrated burning rates up to approximately six times the laminar burning rate are obtained. It is shown that increased flame surface area accounts for most of the enhanced burning while increases in the burning rate per unit area also play an important contribution.The database is then used to assess a new model of flame wrinkling intended for large-eddy simulations (LES). The approach draws on concepts from fractal geometry, requiring the modelling of an inner cut-off scale representing the smallest scale of flame wrinkling, and the fractal dimension controlling the resolution dependence of the unresolved flame surface area. In contrast to previous modelling, it is argued that the inner cut-off should be filter-size invariant in an inertial range. Then, dimensional and physical reasoning together with Damköhler’s limiting scaling laws for the turbulent flame speed are used to infer the cut-off and fractal dimension in limiting regimes. Two methods of determining the fractal dimension are proposed: a static, algebraic expression or a dynamic approach exploiting a Germano-type identity. Finally the model is compared against the DNS in a priori tests and is found to give excellent results, quantitatively capturing the trends with time, space, filter size and Damköhler number.

Research paper thumbnail of On the fractal characteristics of low Damköhler number flames

Combustion and Flame, 2013

ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used t... more ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used to help develop turbulent combustion models. Here, direct numerical simulations of low Damkohler number flames are used to analyse the fractal nature of the flames. Two sets of data are considered: (i) thermochemical hydrogen-air turbulent premixed plane-jet flames with detailed chemistry and (ii) thermonuclear flames in type la supernovae. A three-dimensional box counting method is used to investigate fractal dimension of the flame surface, characterising the self similarity of flame fronts. In the premixed flames, the fractal dimension is found to vary in time between 2.1 and 2.7. The supernovae flames in distributed combustion regimes yield fractal dimension about 2.7. The results for the maximum fractal dimensions are higher than previously reported. They are explained theoretically by a Reynolds number similarity argument which posits that the high Reynolds number, low Damkohler number limiting value of the fractal dimension is 8/3. Also tested is Mandelbrot's fractal additive law which relates the fractal dimension determined in two dimensions, which is typical of experimental measurements, to that in three dimensions. The comparison of the fractal dimension in both two-dimensional and three-dimensional spaces supports the additive law, even though the flames considered do not formally satisfy isotropy. Finally, the inner-cut off is extracted from the hydrogen flames and found to be consistent in order of magnitude with Kolmogorov scaling.

Research paper thumbnail of A posteriori large-eddy simulations of a turbulent premixed flame in the thin reaction zones regime

Large-eddy simulations (LES) have been successfully applied to premixed turbulent flames in the f... more Large-eddy simulations (LES) have been successfully applied to premixed turbulent flames in the flamelet regime. However, in the context of LES, comparatively little effort has focused on modelling of premixed flames in regimes of combustion in which the small scale eddies can penetrate the flame, the most important of which is the so-called thin-reaction zones (TRZ) regime. In this work, a posteriori LES of a turbulent premixed, methaneair slot-jet are performed using strained and unstrained premixed flamelet ...

Research paper thumbnail of On the fractal characteristics of low Damköhler number flames

Combustion and Flame, Nov 1, 2013

ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used t... more ABSTRACT Knowledge of the fractal properties of premixed flame surfaces can potentially be used to help develop turbulent combustion models. Here, direct numerical simulations of low Damkohler number flames are used to analyse the fractal nature of the flames. Two sets of data are considered: (i) thermochemical hydrogen-air turbulent premixed plane-jet flames with detailed chemistry and (ii) thermonuclear flames in type la supernovae. A three-dimensional box counting method is used to investigate fractal dimension of the flame surface, characterising the self similarity of flame fronts. In the premixed flames, the fractal dimension is found to vary in time between 2.1 and 2.7. The supernovae flames in distributed combustion regimes yield fractal dimension about 2.7. The results for the maximum fractal dimensions are higher than previously reported. They are explained theoretically by a Reynolds number similarity argument which posits that the high Reynolds number, low Damkohler number limiting value of the fractal dimension is 8/3. Also tested is Mandelbrot's fractal additive law which relates the fractal dimension determined in two dimensions, which is typical of experimental measurements, to that in three dimensions. The comparison of the fractal dimension in both two-dimensional and three-dimensional spaces supports the additive law, even though the flames considered do not formally satisfy isotropy. Finally, the inner-cut off is extracted from the hydrogen flames and found to be consistent in order of magnitude with Kolmogorov scaling.

Research paper thumbnail of Effect of Oxygen Enrichment on Methane Ignition

Social Science Research Network, 2023

Research paper thumbnail of An Updated Functional-Group-Based Approach to Modeling the Vacuum Residue Oil Gasification Kinetics

Research paper thumbnail of Effect of Water Vapor on the Oxidation of Heavy Fuel and Vacuum Residue Oil in a Tga

Research paper thumbnail of An Updated Functional-Group-Based Approach to Modeling the Vacuum Residue Oil Gasification Kinetics

Research paper thumbnail of Effect of pressure and CO2 dilution on soot formation in laminar inverse coflow flame at conditions close to autothermal reforming

Research paper thumbnail of Effect of Oxygen Enrichment on Methane Ignition

Research paper thumbnail of TG-DSC and TG-FTIR analysis of heavy fuel oil and vacuum residual oil pyrolysis and combustion: characterization, kinetics, and evolved gas analysis

Journal of Thermal Analysis and Calorimetry

Research paper thumbnail of Heavy-Oil Surrogate Formulation Based on Ft-Icr Ms Analysis

SSRN Electronic Journal

Generally, surrogate molecules are used to represent complex oil mixtures for property prediction... more Generally, surrogate molecules are used to represent complex oil mixtures for property predictions and kinetic model development. The aim of a surrogate formulation is to represent the chemical and physical properties of a complex oil matrix with a single molecule or only a few species. The chemical kinetic model of the proposed surrogate can be used to simulate oil behavior in different scenarios such as pyrolysis and oxidation. However, the surrogate formulation of heavy oils requires a characterization using many chemical analytical techniques, which are expensive, time-consuming, and hard to interpret. This study presents a new heavy oil surrogate formulation methodology based only on high-resolution mass spectrometry. The methodology was used to

Research paper thumbnail of Soot production in high pressure inverse diffusion flames with enriched oxygen in the oxidizer stream

Research paper thumbnail of The effect of preheating temperature on PAH/soot formation in methane/air co-flow flames at elevated pressure

Research paper thumbnail of 18th Australasian Fluid Mechanics Conference

A posteriori large-eddy simulations of a turbulent premixed flame in the thin reaction zones regime