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Nilanjan Chakraborty - One of the best experts on this subject based on the ideXlab platform.
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assessment of algebraic flame surface density closures in the context of large eddy simulations of head on quenching of Turbulent premixed flames
Combustion Science and Technology, 2017Co-Authors: Jiawei Lai, M Klein, Nilanjan ChakrabortyAbstract:ABSTRACTThe applicability of algebraic large eddy simulation (LES) closures of flame surface density (FSD) for head-on quenching of premixed Turbulent flames by an isothermal inert wall has been assessed using 3D direct numerical simulations (DNS) data for different values of root-mean-square Turbulent Velocity Fluctuation, Damkohler and Karlovitz numbers. An algebraic FSD closure, which has been reported to perform relatively satisfactorily among several available models, has been considered for this analysis alongside a model, which has recently been used for LES of flame-wall interaction. The applicability of previously proposed near-wall damping factors for flame surface wrinkling and consumption rate in the context of Reynolds Averaged Navier Stokes (RANS) simulations has also been assessed for LES based on the current a-priori DNS analysis. It has been found that existing models considered for this analysis do not predict the near-wall behavior of the FSD accurately for all cases considered here. Fu...
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numerical investigation of localised forced ignition of pulverised coal particle laden mixtures a direct numerical simulation dns analysis
Fuel, 2015Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Abstract Localised forced ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations for the carrier phase with simplified chemistry for the combustion of volatile gases. The coal particles are treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases has been achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis has been carried out to analyse the effects of particle equivalence ratio Φ p (which is defined based on the total available primary volatile fuel in the particulate phase), root-mean-square of Turbulent Velocity u ′ and particle diameter d p on the early stages of combustion. Both non-premixed and premixed modes of combustion have been observed in the reaction zone for the flames resulting from localised ignition. An increase in Φ p is found to be detrimental for sustaining combustion, whereas a reduction in particle size may adversely affect the extent of burning. It has been found that an increase in u ′ increases the rate of mixing of devolatilised fuel with the surrounding air, which, though beneficial for sustaining combustion, increases the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of u ′. Detailed physical explanations have been provided to explain the observed effects of Φ p , root-mean-square Turbulent Velocity Fluctuation u ′ and particle diameter d p on combustion of coal particle-laden mixtures following successful localised forced ignition.
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assessment of the performances of sub grid scalar flux models for premixed flames with different global lewis numbers a direct numerical simulation analysis
International Journal of Heat and Fluid Flow, 2015Co-Authors: Y Gao, Nilanjan Chakraborty, M KleinAbstract:Abstract The statistical behaviours of sub-grid flux of reaction progress variable has been assessed for premixed Turbulent flames with global Lewis number Le (=thermal diffusivity/mass diffusivity) ranging from 0.34 to 1.2 using a Direct Numerical Simulation (DNS) database of freely propagating statistically planar flames. It is known that the sub-grid scalar flux shows counter-gradient transport when the Velocity jump across the flame due to heat release overcomes the effects of Turbulent Velocity Fluctuation. The results show that the sub-grid scalar flux components exhibit counter-gradient transport for all cases considered here. The extent of counter-gradient transport increases with increasing filter width Δ and decreasing value of Le . This is due to the fact that flames with Le ≪ 1 (e.g. Le = 0.34) exhibit thermo-diffusive instabilities, which in turn increases the extent of counter-gradient transport. The effects of heat release and flame normal acceleration weaken with increasing Le . Several established algebraic models have been assessed in comparison to the sub-grid scalar flux components extracted from explicitly filtered DNS data in terms of their correlation coefficients at the vector level and their mean variation conditional on the Favre-filtered progress variable. The gradient transport closure does neither capture the quantitative nor the qualitative behaviour of the different sub-grid scalar flux components for all filter widths in all cases considered here. Models which account for local flame normal acceleration perform better, especially when the flame remains completely unresolved. In particular those models that account for the alignment of local resolved Velocity and scalar gradients by using a tensor diffusivity, perform relatively better than the other alternative models irrespective of Le .
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Effects of Equivalence Ratio and Turbulent Velocity Fluctuation on Early Stages of Pulverized Coal Combustion Following Localized Ignition: A Direct Numerical Simulation Analysis
Energy & Fuels, 2014Co-Authors: Tamir Brosh, Nilanjan ChakrabortyAbstract:This study utilized three-dimensional direct numerical simulations (DNS) in order to analyze the effects of Turbulent Velocity Fluctuation, equivalence ratio based on volatile primary fuel in the p...
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Localised Forced Ignition of Pulverised Coal Particle-Laden Mixtures: A Direct Numerical Simulation Analysis
2014Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Localised ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations with simplified chemistry for the combustion of volatile gases. The coal particles were treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases was achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis was carried out to analyse the effects of particle equivalence ratio , root-mean-square Turbulent Velocity Fluctuation and particle diameter on selfsustained combustion following successful ignition. An increase in has an adverse effect on self-sustained combustion, whereas a reduction in particle size may have detrimental effects on the extent of burning. It was found that an increase in increases the rate of mixing of devolatilised fuel with the surrounding air, which though beneficial, for self-sustained combustion, augments the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of . Detailed physical explanations were provided to explain the observed effects of , root-mean-square Turbulent Velocity Fluctuation and particle diameter on self-sustained combustion of coal particle-laden mixtures.
Tamir Brosh - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of localised forced ignition of pulverised coal particle laden mixtures a direct numerical simulation dns analysis
Fuel, 2015Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Abstract Localised forced ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations for the carrier phase with simplified chemistry for the combustion of volatile gases. The coal particles are treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases has been achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis has been carried out to analyse the effects of particle equivalence ratio Φ p (which is defined based on the total available primary volatile fuel in the particulate phase), root-mean-square of Turbulent Velocity u ′ and particle diameter d p on the early stages of combustion. Both non-premixed and premixed modes of combustion have been observed in the reaction zone for the flames resulting from localised ignition. An increase in Φ p is found to be detrimental for sustaining combustion, whereas a reduction in particle size may adversely affect the extent of burning. It has been found that an increase in u ′ increases the rate of mixing of devolatilised fuel with the surrounding air, which, though beneficial for sustaining combustion, increases the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of u ′. Detailed physical explanations have been provided to explain the observed effects of Φ p , root-mean-square Turbulent Velocity Fluctuation u ′ and particle diameter d p on combustion of coal particle-laden mixtures following successful localised forced ignition.
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Effects of Equivalence Ratio and Turbulent Velocity Fluctuation on Early Stages of Pulverized Coal Combustion Following Localized Ignition: A Direct Numerical Simulation Analysis
Energy & Fuels, 2014Co-Authors: Tamir Brosh, Nilanjan ChakrabortyAbstract:This study utilized three-dimensional direct numerical simulations (DNS) in order to analyze the effects of Turbulent Velocity Fluctuation, equivalence ratio based on volatile primary fuel in the p...
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Localised Forced Ignition of Pulverised Coal Particle-Laden Mixtures: A Direct Numerical Simulation Analysis
2014Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Localised ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations with simplified chemistry for the combustion of volatile gases. The coal particles were treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases was achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis was carried out to analyse the effects of particle equivalence ratio , root-mean-square Turbulent Velocity Fluctuation and particle diameter on selfsustained combustion following successful ignition. An increase in has an adverse effect on self-sustained combustion, whereas a reduction in particle size may have detrimental effects on the extent of burning. It was found that an increase in increases the rate of mixing of devolatilised fuel with the surrounding air, which though beneficial, for self-sustained combustion, augments the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of . Detailed physical explanations were provided to explain the observed effects of , root-mean-square Turbulent Velocity Fluctuation and particle diameter on self-sustained combustion of coal particle-laden mixtures.
Prasun Dutta - One of the best experts on this subject based on the ideXlab platform.
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visibility moments and power spectrum of turbulence Velocity
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Prasun DuttaAbstract:Here we introduce moments of visibility function and discuss how those can be used to estimate the power spectrum of the Turbulent Velocity of external spiral galaxies. We perform numerical simulation to confirm the credibility of this method and found that for galaxies with lower inclination angles it works fine. This is the only method to estimate the power spectrum of the Turbulent Velocity Fluctuation in the ISM of the external galaxies.
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effect of Turbulent Velocity on the h i intensity Fluctuation power spectrum from spiral galaxies
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Prasun DuttaAbstract:We use numerical simulations to investigate effect of Turbulent Velocity on the power spectrum of H i intensity from external galaxies when (a) all emission is considered, (b) emission with Velocity range smaller than the Turbulent Velocity dispersion is considered. We found that for case (a) the intensity Fluctuation depends directly only on the power spectrum of the column density, whereas for case (b) it depends only on the Turbulent Velocity Fluctuation. We discuss the implications of this result in real observations of H i Fluctuations.
Daniel H. Wacks - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of localised forced ignition of pulverised coal particle laden mixtures a direct numerical simulation dns analysis
Fuel, 2015Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Abstract Localised forced ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations for the carrier phase with simplified chemistry for the combustion of volatile gases. The coal particles are treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases has been achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis has been carried out to analyse the effects of particle equivalence ratio Φ p (which is defined based on the total available primary volatile fuel in the particulate phase), root-mean-square of Turbulent Velocity u ′ and particle diameter d p on the early stages of combustion. Both non-premixed and premixed modes of combustion have been observed in the reaction zone for the flames resulting from localised ignition. An increase in Φ p is found to be detrimental for sustaining combustion, whereas a reduction in particle size may adversely affect the extent of burning. It has been found that an increase in u ′ increases the rate of mixing of devolatilised fuel with the surrounding air, which, though beneficial for sustaining combustion, increases the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of u ′. Detailed physical explanations have been provided to explain the observed effects of Φ p , root-mean-square Turbulent Velocity Fluctuation u ′ and particle diameter d p on combustion of coal particle-laden mixtures following successful localised forced ignition.
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Localised Forced Ignition of Pulverised Coal Particle-Laden Mixtures: A Direct Numerical Simulation Analysis
2014Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Localised ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations with simplified chemistry for the combustion of volatile gases. The coal particles were treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases was achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis was carried out to analyse the effects of particle equivalence ratio , root-mean-square Turbulent Velocity Fluctuation and particle diameter on selfsustained combustion following successful ignition. An increase in has an adverse effect on self-sustained combustion, whereas a reduction in particle size may have detrimental effects on the extent of burning. It was found that an increase in increases the rate of mixing of devolatilised fuel with the surrounding air, which though beneficial, for self-sustained combustion, augments the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of . Detailed physical explanations were provided to explain the observed effects of , root-mean-square Turbulent Velocity Fluctuation and particle diameter on self-sustained combustion of coal particle-laden mixtures.
Dipal Patel - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of localised forced ignition of pulverised coal particle laden mixtures a direct numerical simulation dns analysis
Fuel, 2015Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Abstract Localised forced ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations for the carrier phase with simplified chemistry for the combustion of volatile gases. The coal particles are treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases has been achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis has been carried out to analyse the effects of particle equivalence ratio Φ p (which is defined based on the total available primary volatile fuel in the particulate phase), root-mean-square of Turbulent Velocity u ′ and particle diameter d p on the early stages of combustion. Both non-premixed and premixed modes of combustion have been observed in the reaction zone for the flames resulting from localised ignition. An increase in Φ p is found to be detrimental for sustaining combustion, whereas a reduction in particle size may adversely affect the extent of burning. It has been found that an increase in u ′ increases the rate of mixing of devolatilised fuel with the surrounding air, which, though beneficial for sustaining combustion, increases the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of u ′. Detailed physical explanations have been provided to explain the observed effects of Φ p , root-mean-square Turbulent Velocity Fluctuation u ′ and particle diameter d p on combustion of coal particle-laden mixtures following successful localised forced ignition.
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Localised Forced Ignition of Pulverised Coal Particle-Laden Mixtures: A Direct Numerical Simulation Analysis
2014Co-Authors: Tamir Brosh, Dipal Patel, Daniel H. Wacks, Nilanjan ChakrabortyAbstract:Localised ignition of mono-disperse pulverised coal particle-laden mixtures has been analysed based on three-dimensional Direct Numerical Simulations with simplified chemistry for the combustion of volatile gases. The coal particles were treated as point sources and tracked in a Lagrangian manner. The coupling between Eulerian gaseous and Lagrangian particulate phases was achieved by appropriate source terms in the mass, momentum, energy and species conservation equations. A detailed parametric analysis was carried out to analyse the effects of particle equivalence ratio , root-mean-square Turbulent Velocity Fluctuation and particle diameter on selfsustained combustion following successful ignition. An increase in has an adverse effect on self-sustained combustion, whereas a reduction in particle size may have detrimental effects on the extent of burning. It was found that an increase in increases the rate of mixing of devolatilised fuel with the surrounding air, which though beneficial, for self-sustained combustion, augments the heat transfer rate from the hot gas kernel, thus leading to flame extinction for high values of . Detailed physical explanations were provided to explain the observed effects of , root-mean-square Turbulent Velocity Fluctuation and particle diameter on self-sustained combustion of coal particle-laden mixtures.
