The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Nedunchezhian Swaminathan - One of the best experts on this subject based on the ideXlab platform.
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spatial correlation of heat release rate and Sound emission from turbulent premixed flames
Combustion and Flame, 2012Co-Authors: Yu Liu, Nedunchezhian Swaminathan, Ann P. Dowling, T D DunstanAbstract:The two-point spatial correlation of the rate of change of fluctuating heat release rate is central to the Sound emission from open turbulent flames, and a few attempts have been made to address this correlation in recent studies. In this paper, the two-point correlation and its role in combustion noise are studied by analysing direct numerical simulation (DNS) data of statistically multi-dimensional turbulent premixed flames. The results suggest that this correlation function depends on the separation distance and direction but, not on the positions inside the flame brush. This correlation can be modelled using a combination of Hermite–Gaussian functions of zero and second order, i.e. functions of the form (1-Ax²)exp(-Bx²) for constants A and B, to include its possible negative values. The integral correlation volume obtained using this model is about 0.2δL³ with the length scale obtained from its cube root being about 0.6δL, where δL is the laminar flame thermal thickness. Both of the values are slightly larger than the values reported in an earlier study because of the anisotropy observed for the correlation. This model together with the turbulence-dependent parameter Κ, the ratio of the root-mean-square (RMS) value of the rate of change of reaction rate to the mean reaction rate, derived from the DNS data is applied to predict the Far-Field Sound emitted from open flames. The calculated noise levels agree well with recently reported measurements and show a sensitivity to Κ values.
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heat release rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The Sound emission from open turbulent flames is dictated by the two-point spatial correlation of the rate of change of the fluctuating heat release rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating heat release rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction rate closure, involving a recently developed scalar dissipation rate model, are used to obtain the Far-Field Sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of heat release rate is low.
R. Balachandran - One of the best experts on this subject based on the ideXlab platform.
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heat release rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The Sound emission from open turbulent flames is dictated by the two-point spatial correlation of the rate of change of the fluctuating heat release rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating heat release rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction rate closure, involving a recently developed scalar dissipation rate model, are used to obtain the Far-Field Sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of heat release rate is low.
Jonathan B. Freund - One of the best experts on this subject based on the ideXlab platform.
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a model supersonic buried nozzle jet instability and acoustic wave scattering and the far field Sound
Journal of Fluid Mechanics, 2015Co-Authors: Arnab Samanta, Jonathan B. FreundAbstract:We consider Sound source mechanisms involving the acoustic and instability modes of dual-stream isothermal supersonic jets with the inner nozzle buried within an outer shroud-like nozzle. A particular focus is scattering into radiating Sound waves at the shroud lip. For such jets, several families of acoustically coupled instability waves exist, beyond the regular vortical Kelvin-Helmholtz mode, with different shapes and propagation characteristics, which can therefore affect the character of the radiated Sound. In our model, the coaxial shear layers are vortex sheets while the incident acoustic disturbances are the propagating shroud modes. The Wiener-Hopf method is used to compute their scattering at the sharp shroud edge to obtain the Far-Field radiation. The resulting Far-Field directivity quantifies the acoustic efficiency of different mechanisms, which is particularly important in the upstream direction, where the results show that the scattered Sound is more intense than that radiated directly by the shear-layer modes.
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very near nozzle shear layer turbulence and jet noise
Journal of Fluid Mechanics, 2015Co-Authors: Ryan A Fontaine, Joanna Austin, Gregory S Elliott, Jonathan B. FreundAbstract:One of the principal challenges in the prediction and design of low-noise nozzles is accounting for the near-nozzle turbulent mixing layers at the high Reynolds numbers of engineering conditions. Even large-eddy simulation is a challenge because the locally largest scales are so small relative to the nozzle diameter. Model-scale experiments likewise typically have relatively thick near-nozzle shear layers, which potentially hampers their applicability to high-Reynolds-number design. To quantify the sensitivity of the Far-Field Sound to nozzle turbulent-shear-layer conditions, a family of diameter $D$ nozzles is studied in which the exit turbulent boundary layer momentum thickness is varied from $0.0042D$ up to $0.021D$ for otherwise identical flow conditions. Measurements include particle image velocimetry (PIV) to within $0.04D$ of the exit plane and Far-Field acoustic spectra. The influence of the initial turbulent-shear-layer thickness is pronounced, though it is less significant than the well-known sensitivity of the Far-Field Sound to laminar versus turbulent shear-layer exit conditions. For thicker shear layers, the nominally missing region, where the corresponding thinner shear layer would develop, leads to the noise difference. The nozzle-exit momentum thickness successfully scales the high-frequency radiated Sound for nozzles of different sizes and exhaust conditions. Yet, despite this success, the detailed turbulence statistics show distinct signatures of the different nozzle boundary layers from the different nozzles. Still, the different nozzle shear-layer thicknesses and shapes have a similar downstream development, which is consistent with a linear stability analysis of the measured velocity profiles.
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very near nozzle shear layer turbulence and jet noise
Journal of Fluid Mechanics, 2015Co-Authors: Ryan A Fontaine, Joanna Austin, Gregory S Elliott, Jonathan B. FreundAbstract:One of the principal challenges in the prediction and design of low-noise nozzles is accounting for the near-nozzle turbulent mixing layers at the high Reynolds numbers of engineering conditions. Even large-eddy simulation is a challenge because the locally largest scales are so small relative to the nozzle diameter. Model-scale experiments likewise typically have relatively thick near-nozzle shear layers, which potentially hampers their applicability to high-Reynolds-number design. To quantify the sensitivity of the Far-Field Sound to nozzle turbulent-shear-layer conditions, a family of diameter $D$ nozzles is studied in which the exit turbulent boundary layer momentum thickness is varied from $0.0042D$ up to $0.021D$ for otherwise identical flow conditions. Measurements include particle image velocimetry (PIV) to within $0.04D$ of the exit plane and Far-Field acoustic spectra. The influence of the initial turbulent-shear-layer thickness is pronounced, though it is less significant than the well-known sensitivity of the Far-Field Sound to laminar versus turbulent shear-layer exit conditions. For thicker shear layers, the nominally missing region, where the corresponding thinner shear layer would develop, leads to the noise difference. The nozzle-exit momentum thickness successfully scales the high-frequency radiated Sound for nozzles of different sizes and exhaust conditions. Yet, despite this success, the detailed turbulence statistics show distinct signatures of the different nozzle boundary layers from the different nozzles. Still, the different nozzle shear-layer thicknesses and shapes have a similar downstream development, which is consistent with a linear stability analysis of the measured velocity profiles.
Ann P. Dowling - One of the best experts on this subject based on the ideXlab platform.
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spatial correlation of heat release rate and Sound emission from turbulent premixed flames
Combustion and Flame, 2012Co-Authors: Yu Liu, Nedunchezhian Swaminathan, Ann P. Dowling, T D DunstanAbstract:The two-point spatial correlation of the rate of change of fluctuating heat release rate is central to the Sound emission from open turbulent flames, and a few attempts have been made to address this correlation in recent studies. In this paper, the two-point correlation and its role in combustion noise are studied by analysing direct numerical simulation (DNS) data of statistically multi-dimensional turbulent premixed flames. The results suggest that this correlation function depends on the separation distance and direction but, not on the positions inside the flame brush. This correlation can be modelled using a combination of Hermite–Gaussian functions of zero and second order, i.e. functions of the form (1-Ax²)exp(-Bx²) for constants A and B, to include its possible negative values. The integral correlation volume obtained using this model is about 0.2δL³ with the length scale obtained from its cube root being about 0.6δL, where δL is the laminar flame thermal thickness. Both of the values are slightly larger than the values reported in an earlier study because of the anisotropy observed for the correlation. This model together with the turbulence-dependent parameter Κ, the ratio of the root-mean-square (RMS) value of the rate of change of reaction rate to the mean reaction rate, derived from the DNS data is applied to predict the Far-Field Sound emitted from open flames. The calculated noise levels agree well with recently reported measurements and show a sensitivity to Κ values.
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heat release rate correlation and combustion noise in premixed flames
Journal of Fluid Mechanics, 2011Co-Authors: Nedunchezhian Swaminathan, Ann P. Dowling, R. BalachandranAbstract:The Sound emission from open turbulent flames is dictated by the two-point spatial correlation of the rate of change of the fluctuating heat release rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating heat release rate is deduced to be about tau(c)/34 on an average, where tau(c) is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction rate obtained from Reynolds-averaged Navier-Stokes (RANS) calculations of open turbulent premixed flames employing the standard (k) over tilde-(epsilon) over tilde model and an algebraic reaction rate closure, involving a recently developed scalar dissipation rate model, are used to obtain the Far-Field Sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of heat release rate is low.
T D Dunstan - One of the best experts on this subject based on the ideXlab platform.
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spatial correlation of heat release rate and Sound emission from turbulent premixed flames
Combustion and Flame, 2012Co-Authors: Yu Liu, Nedunchezhian Swaminathan, Ann P. Dowling, T D DunstanAbstract:The two-point spatial correlation of the rate of change of fluctuating heat release rate is central to the Sound emission from open turbulent flames, and a few attempts have been made to address this correlation in recent studies. In this paper, the two-point correlation and its role in combustion noise are studied by analysing direct numerical simulation (DNS) data of statistically multi-dimensional turbulent premixed flames. The results suggest that this correlation function depends on the separation distance and direction but, not on the positions inside the flame brush. This correlation can be modelled using a combination of Hermite–Gaussian functions of zero and second order, i.e. functions of the form (1-Ax²)exp(-Bx²) for constants A and B, to include its possible negative values. The integral correlation volume obtained using this model is about 0.2δL³ with the length scale obtained from its cube root being about 0.6δL, where δL is the laminar flame thermal thickness. Both of the values are slightly larger than the values reported in an earlier study because of the anisotropy observed for the correlation. This model together with the turbulence-dependent parameter Κ, the ratio of the root-mean-square (RMS) value of the rate of change of reaction rate to the mean reaction rate, derived from the DNS data is applied to predict the Far-Field Sound emitted from open flames. The calculated noise levels agree well with recently reported measurements and show a sensitivity to Κ values.
