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S.s. Shy - One of the best experts on this subject based on the ideXlab platform.
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Measurements of Fractal Properties of Premixed Turbulent Flames and Their Relation to Turbulent Burning Velocities
Journal of Mechanics, 2001Co-Authors: S.i. Yang, S.s. ShyAbstract:The fractal properties of premixed transient flames propagating downwards through a near-isotropic turbulent flow field in a fan-stirred cruciform burner were investigated. The long vertical section of the cruciform burner was used to provide a downward propagating premixed flame at 1 atm. The large Horizontal Vessel equipped with a pair of counter-rotating fans and perforated plates at each end was used to generate near-isotropic turbulence. Turbulent flame front images were obtained using high-speed laser sheet imaging for both methane-air and propane-air mixtures. The nondimensional turbulent intensity ( u ′/S L ), Reynolds number based on the integral length scale, and turbulent Karlovitz number were varied from 1 to 10, from 698 to 6032, and from 0.05 to 1.43, respectively. Hundreds of runs for each experimental condition were carried out to obtain sufficient images of these turbulent transient flame fronts just in the central uniform region. These images were then processed to extract fractal dimension, inner and outer cutoffs using both the circle and the caliper methods. It was found that the mean fractal dimension is only 2.18, nearly independent of u ′/S L , in support of recent Bunsen-flame results found by Gulder and his co-workers. This contradicts the findings of many previous studies in which the fractal dimension may approach asymptotically to a value of 2.33 when u ′/S L > 3. The inner (e i ) and outer (e 0 ) cutoffs are found to be nearly constant for all flames studied, where e 0 is an order of magnitude greater than e i and it is smaller than the integral length scale of unreacted turbulence. Finally, the present fractal characteristics cannot predict turbulent burning velocities correctly when the available fractal closure model was used, indicating a limit of the fractal analysis on prediction of turbulent burning velocities.
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Measurements of Fractal Properties of Premixed Turbulent Flames and Their Relation to Turbulent Burning Velocities
Journal of Mechanics, 2001Co-Authors: S.i. Yang, S.s. ShyAbstract:ABSTRACTThe fractal properties of premixed transient flames propagating downwards through a near-isotropic turbulent flow field in a fan-stirred cruciform burner were investigated. The long vertical section of the cruciform burner was used to provide a downward propagating premixed flame at 1 atm. The large Horizontal Vessel equipped with a pair of counter-rotating fans and perforated plates at each end was used to generate near-isotropic turbulence. Turbulent flame front images were obtained using high-speed laser sheet imaging for both methane-air and propane-air mixtures. The nondimensional turbulent intensity (u′/SL), Reynolds number based on the integral length scale, and turbulent Karlovitz number were varied from 1 to 10, from 698 to 6032, and from 0.05 to 1.43, respectively. Hundreds of runs for each experimental condition were carried out to obtain sufficient images of these turbulent transient flame fronts just in the central uniform region. These images were then processed to extract fractal dimension, inner and outer cutoffs using both the circle and the caliper methods. It was found that the mean fractal dimension is only 2.18, nearly independent of u′/SL, in support of recent Bunsen-flame results found by Gülder and his co-workers. This contradicts the findings of many previous studies in which the fractal dimension may approach asymptotically to a value of 2.33 when u′/SL > 3. The inner (εi) and outer (ε0) cutoffs are found to be nearly constant for all flames studied, where ε0 is an order of magnitude greater than εi and it is smaller than the integral length scale of unreacted turbulence. Finally, the present fractal characteristics cannot predict turbulent burning velocities correctly when the available fractal closure model was used, indicating a limit of the fractal analysis on prediction of turbulent burning velocities.
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A new cruciform burner and its turbulence measurements for premixed turbulent combustion study
Experimental Thermal and Fluid Science, 2000Co-Authors: S.s. Shy, M.l. LinAbstract:Abstract A new turbulent flow system is proposed for the study of premixed turbulent combustion processes. This cruciform burner consists of two cylindrical Vessels. The long vertical Vessel can provide a stable downward propagating premixed-flame at one atmosphere. The Horizontal Vessel was equipped with a pair of motor-driven fans and perforated plates at each end. The fans can generate two intense counter-rotating large vortical streams with controllable fan frequency up to 7620 rpm. It was found that an approximately isotropic stationary turbulence with large turbulent intensities (greater than 450 cm/s) located in the core region between two perforated plates can be generated, as verified by extensive LDV measurements. In that mean velocities are nearly zero, turbulent intensities in all three directions are roughly equal, and the energy spectrum has a −5/3 slope, indicating that the turbulence has some properties of isotropic turbulence. Other parameters of interest, such as the autocorrelation, the integral length scale, and the experimental uncertainties are also reported for the first time. The present turbulence generator can be conveniently adopted for many experimental studies, such as gaseous premixed flames propagation and particle settling in nearly isotropic turbulence.
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DIRECT AND INDIRECT MEASUREMENTS OF FLAME SURFACE DENSITY, ORIENTATION, AND CURVATURE FOR PREMIXED TURBULENT COMBUSTION MODELING IN A CRUCIFORM BURNER
Proceedings of the Combustion Institute, 2000Co-Authors: S.s. Shy, E.i. Lee, N.w. Chang, S.i. YangAbstract:This paper analyzes experimentally the Bray–Moss–Libby (BML) model and the flame surface density (R) transport equation using premixed flames propagating through isotropic turbulence in a new cruciform burner and, thus, makes the analogy in both cases for the first time. The burner consists of a long vertical Vessel that provides a downward propagating, lean premixed C3H8/air flame and a Horizontal Vessel. The latter is equipped with a pair of counter-rotating fans and perforated plates at each end to generate nearisotropic turbulence between two perforated plates. Visualization of turbulent flame fronts is obtained from high-speed laser sheet imaging. Several hundred runs at the same experimental conditions are carried out to obtain sufficient images in the central uniform region that are then processed to extract flame wrinkling
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High-intensity turbulent premixed combustion: General correlations of turbulent burning velocities in a new cruciform burner
Proceedings of the Combustion Institute, 2000Co-Authors: S.s. Shy, W.j. Lin, K.z. PengAbstract:A methodology was developed to investigate general correlations of turbulent burning velocities for high-intensity premixed turbulent combustion. The burner consists of two Vessels with a cruciform shape. The long vertical Vessel provides a stable, downward-propagating premixed flame, while the Horizontal Vessel is equipped with a pair of counter-rotating fans and perforated plates at each end to generate high-intensity isotropic turbulence. Using a pair of specially designed ion-probe sensors, turbulent burning velocities of both methane-air and propane-air mixtures are quantitatively measured over a greater parameter range than hitherto measured. These turbulent burning rates are then compared with earlier results using different burners. When Bradley's dimensionless correlations in terms of the Lewis, turbulent Karlovitz, and Reynolds numbers are used to analyze the present data, great caution in smoothing large scattering data of S T / S L against u′/S L is required. Our present S T / S L data are generally smaller than that of Bradley by a factor of 2 at any fixed u′/S L . Interestingly, when the Lewis number is less than unity, no global quenching of turbulent premixed flames is observed event at u′/S L ≈50, a value significantly higher than hitherto used. Finally, a general correlation of the form ( S T - S L )/ u′ ≈0.05 Da 0.61 , is proposed, where Da is the Damkohler number. This correlation is better than previous correlations, which covers both distributed (small Da ) and corrugated flamelet (large Da ) regimes.
M. R. Turner - One of the best experts on this subject based on the ideXlab platform.
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Numerical simulations of dynamic coupling between shallow-water sloshing and Horizontal Vessel motion with baffles
Fluid Dynamics Research, 2016Co-Authors: H. Alemi Ardakani, M. R. TurnerAbstract:The coupled motion between shallow water sloshing in a moving Vessel with baffles and the Vessel dynamics is considered. Here the Vessel dynamics is restricted to Horizontal motion such as in Tuned Liquid Dampers. It was shown by Turner {\it et al.} \cite{tbaa} (Phys. Fluids (2013) {\bf 25}(10) 112102) that partitioning a moving Vessel into $n$ separate compartments leads to an interesting dynamical behaviour of the system. Also, under particular input parameter values an internal $(n+1)$-fold $1:\cdots:1$ resonance can be generated, where the frequency of the sloshing fluid in each compartment is equal, and equal to the frequency of the Vessel itself. Here the form of the sloshing eigenmodes at this resonance are derived in the shallow-water limit. Using the Lagrangian formulation of the problem, an efficient numerical algorithm is implemented to solve the fully nonlinear system of equation based on the implicit midpoint rule. This algorithm is simple, fast and maintains the energy partition between the Vessel and the fluid over long times. In this work numerical results are presented for dynamical Vessel/sloshing motion attached to a nonlinear spring.
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Dynamic coupling between Horizontal Vessel motion and two-layer shallow-water sloshing
Journal of Fluids and Structures, 2015Co-Authors: H. Alemi Ardakani, Thomas J. Bridges, M. R. TurnerAbstract:Abstract Numerical and analytical results are presented for fluid sloshing, of a two-layer inviscid, incompressible and immiscible fluid with thin layers and a rigid lid, coupled to a Vessel which is free to undergo Horizontal motion governed by a nonlinear spring. Exact analytical results are obtained for the linear problem, giving the natural frequencies and the resonance structure, particularly between the fluid and Vessel. A numerical method for the linear and nonlinear equations is developed based on the high-resolution f-wave-propagation finite volume methods due to Bale et al. (2002) [SIAM Journal on Scientific Computing 24, 955–978], adapted to include the pressure gradient at the rigid-lid, and coupled to a Runge–Kutta solver for the Vessel motion. The numerical simulations in the linear limit are compared with the exact analytical solutions. The coupled nonlinear numerical solutions with simulations near the internal 1:1 resonance are presented. Of particular interest is the partition of energy between the Vessel and fluid motion.
S.i. Yang - One of the best experts on this subject based on the ideXlab platform.
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Measurements of Fractal Properties of Premixed Turbulent Flames and Their Relation to Turbulent Burning Velocities
Journal of Mechanics, 2001Co-Authors: S.i. Yang, S.s. ShyAbstract:The fractal properties of premixed transient flames propagating downwards through a near-isotropic turbulent flow field in a fan-stirred cruciform burner were investigated. The long vertical section of the cruciform burner was used to provide a downward propagating premixed flame at 1 atm. The large Horizontal Vessel equipped with a pair of counter-rotating fans and perforated plates at each end was used to generate near-isotropic turbulence. Turbulent flame front images were obtained using high-speed laser sheet imaging for both methane-air and propane-air mixtures. The nondimensional turbulent intensity ( u ′/S L ), Reynolds number based on the integral length scale, and turbulent Karlovitz number were varied from 1 to 10, from 698 to 6032, and from 0.05 to 1.43, respectively. Hundreds of runs for each experimental condition were carried out to obtain sufficient images of these turbulent transient flame fronts just in the central uniform region. These images were then processed to extract fractal dimension, inner and outer cutoffs using both the circle and the caliper methods. It was found that the mean fractal dimension is only 2.18, nearly independent of u ′/S L , in support of recent Bunsen-flame results found by Gulder and his co-workers. This contradicts the findings of many previous studies in which the fractal dimension may approach asymptotically to a value of 2.33 when u ′/S L > 3. The inner (e i ) and outer (e 0 ) cutoffs are found to be nearly constant for all flames studied, where e 0 is an order of magnitude greater than e i and it is smaller than the integral length scale of unreacted turbulence. Finally, the present fractal characteristics cannot predict turbulent burning velocities correctly when the available fractal closure model was used, indicating a limit of the fractal analysis on prediction of turbulent burning velocities.
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Measurements of Fractal Properties of Premixed Turbulent Flames and Their Relation to Turbulent Burning Velocities
Journal of Mechanics, 2001Co-Authors: S.i. Yang, S.s. ShyAbstract:ABSTRACTThe fractal properties of premixed transient flames propagating downwards through a near-isotropic turbulent flow field in a fan-stirred cruciform burner were investigated. The long vertical section of the cruciform burner was used to provide a downward propagating premixed flame at 1 atm. The large Horizontal Vessel equipped with a pair of counter-rotating fans and perforated plates at each end was used to generate near-isotropic turbulence. Turbulent flame front images were obtained using high-speed laser sheet imaging for both methane-air and propane-air mixtures. The nondimensional turbulent intensity (u′/SL), Reynolds number based on the integral length scale, and turbulent Karlovitz number were varied from 1 to 10, from 698 to 6032, and from 0.05 to 1.43, respectively. Hundreds of runs for each experimental condition were carried out to obtain sufficient images of these turbulent transient flame fronts just in the central uniform region. These images were then processed to extract fractal dimension, inner and outer cutoffs using both the circle and the caliper methods. It was found that the mean fractal dimension is only 2.18, nearly independent of u′/SL, in support of recent Bunsen-flame results found by Gülder and his co-workers. This contradicts the findings of many previous studies in which the fractal dimension may approach asymptotically to a value of 2.33 when u′/SL > 3. The inner (εi) and outer (ε0) cutoffs are found to be nearly constant for all flames studied, where ε0 is an order of magnitude greater than εi and it is smaller than the integral length scale of unreacted turbulence. Finally, the present fractal characteristics cannot predict turbulent burning velocities correctly when the available fractal closure model was used, indicating a limit of the fractal analysis on prediction of turbulent burning velocities.
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DIRECT AND INDIRECT MEASUREMENTS OF FLAME SURFACE DENSITY, ORIENTATION, AND CURVATURE FOR PREMIXED TURBULENT COMBUSTION MODELING IN A CRUCIFORM BURNER
Proceedings of the Combustion Institute, 2000Co-Authors: S.s. Shy, E.i. Lee, N.w. Chang, S.i. YangAbstract:This paper analyzes experimentally the Bray–Moss–Libby (BML) model and the flame surface density (R) transport equation using premixed flames propagating through isotropic turbulence in a new cruciform burner and, thus, makes the analogy in both cases for the first time. The burner consists of a long vertical Vessel that provides a downward propagating, lean premixed C3H8/air flame and a Horizontal Vessel. The latter is equipped with a pair of counter-rotating fans and perforated plates at each end to generate nearisotropic turbulence between two perforated plates. Visualization of turbulent flame fronts is obtained from high-speed laser sheet imaging. Several hundred runs at the same experimental conditions are carried out to obtain sufficient images in the central uniform region that are then processed to extract flame wrinkling
H. Alemi Ardakani - One of the best experts on this subject based on the ideXlab platform.
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Numerical simulations of dynamic coupling between shallow-water sloshing and Horizontal Vessel motion with baffles
Fluid Dynamics Research, 2016Co-Authors: H. Alemi Ardakani, M. R. TurnerAbstract:The coupled motion between shallow water sloshing in a moving Vessel with baffles and the Vessel dynamics is considered. Here the Vessel dynamics is restricted to Horizontal motion such as in Tuned Liquid Dampers. It was shown by Turner {\it et al.} \cite{tbaa} (Phys. Fluids (2013) {\bf 25}(10) 112102) that partitioning a moving Vessel into $n$ separate compartments leads to an interesting dynamical behaviour of the system. Also, under particular input parameter values an internal $(n+1)$-fold $1:\cdots:1$ resonance can be generated, where the frequency of the sloshing fluid in each compartment is equal, and equal to the frequency of the Vessel itself. Here the form of the sloshing eigenmodes at this resonance are derived in the shallow-water limit. Using the Lagrangian formulation of the problem, an efficient numerical algorithm is implemented to solve the fully nonlinear system of equation based on the implicit midpoint rule. This algorithm is simple, fast and maintains the energy partition between the Vessel and the fluid over long times. In this work numerical results are presented for dynamical Vessel/sloshing motion attached to a nonlinear spring.
-
Dynamic coupling between Horizontal Vessel motion and two-layer shallow-water sloshing
Journal of Fluids and Structures, 2015Co-Authors: H. Alemi Ardakani, Thomas J. Bridges, M. R. TurnerAbstract:Abstract Numerical and analytical results are presented for fluid sloshing, of a two-layer inviscid, incompressible and immiscible fluid with thin layers and a rigid lid, coupled to a Vessel which is free to undergo Horizontal motion governed by a nonlinear spring. Exact analytical results are obtained for the linear problem, giving the natural frequencies and the resonance structure, particularly between the fluid and Vessel. A numerical method for the linear and nonlinear equations is developed based on the high-resolution f-wave-propagation finite volume methods due to Bale et al. (2002) [SIAM Journal on Scientific Computing 24, 955–978], adapted to include the pressure gradient at the rigid-lid, and coupled to a Runge–Kutta solver for the Vessel motion. The numerical simulations in the linear limit are compared with the exact analytical solutions. The coupled nonlinear numerical solutions with simulations near the internal 1:1 resonance are presented. Of particular interest is the partition of energy between the Vessel and fluid motion.
M.l. Lin - One of the best experts on this subject based on the ideXlab platform.
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A new cruciform burner and its turbulence measurements for premixed turbulent combustion study
Experimental Thermal and Fluid Science, 2000Co-Authors: S.s. Shy, M.l. LinAbstract:Abstract A new turbulent flow system is proposed for the study of premixed turbulent combustion processes. This cruciform burner consists of two cylindrical Vessels. The long vertical Vessel can provide a stable downward propagating premixed-flame at one atmosphere. The Horizontal Vessel was equipped with a pair of motor-driven fans and perforated plates at each end. The fans can generate two intense counter-rotating large vortical streams with controllable fan frequency up to 7620 rpm. It was found that an approximately isotropic stationary turbulence with large turbulent intensities (greater than 450 cm/s) located in the core region between two perforated plates can be generated, as verified by extensive LDV measurements. In that mean velocities are nearly zero, turbulent intensities in all three directions are roughly equal, and the energy spectrum has a −5/3 slope, indicating that the turbulence has some properties of isotropic turbulence. Other parameters of interest, such as the autocorrelation, the integral length scale, and the experimental uncertainties are also reported for the first time. The present turbulence generator can be conveniently adopted for many experimental studies, such as gaseous premixed flames propagation and particle settling in nearly isotropic turbulence.