The Experts below are selected from a list of 12471 Experts worldwide ranked by ideXlab platform
M. D. Checkel - One of the best experts on this subject based on the ideXlab platform.
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The importance of turbulence intensity, Eddy Size and flame Size in spark ignited, premixed flame growth
1997Co-Authors: David S.-k. Ting, M. D. CheckelAbstract:The effects of laminar burning velocity, turbulence intensity, flame Size and Eddy Size on the turbulent burning velocity of a premixed growing flame were experimentally separated in a 125 mm cubical chamber with lean methane-air mixtures spark ignited at 1 atm and 300 K. The turbulence was up to 2 m/s with 1 to 4 mm Taylor microscale. For the near unity Lewis number and near zero Markstein number mixture considered here, the turbulent buming velocity, S t , can be approximated as: S t = S l + C d (r/λ)u', where S l is the laminar buming velocity, r is the mean flame radius, λ is the Taylor microscale, u' is the root mean square (r.m.s.) turbulence intensity and C d is a constant of the order 0.02.
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Technical Note: The importance of turbulence intensity, Eddy Size and flame Size in spark ignited, premixed flame growth:
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 1997Co-Authors: David S.-k. Ting, M. D. CheckelAbstract:AbstractThe effects of laminar burning velocity, turbulence intensity, flame Size and Eddy Size on the turbulent burning velocity of a premixed growing flame were experimentally separated in a 125 mm cubical chamber with lean methane-air mixtures spark ignited at 1 atm and 300 K. The turbulence was up to 2 m/s with 1 to 4 mm Taylor microscale. For the near unity Lewis number and near zero Markstein number mixture considered here, the turbulent burning velocity, St, can be approximated as: St = Sl + Cd(r/λ)u′, where Sl is the laminar burning velocity, r is the mean flame radius, λ is the Taylor microscale, u′ is the root mean square (r.m.s.) turbulence intensity and Cd is a constant of the order 0.02.
E. Blay-carreras - One of the best experts on this subject based on the ideXlab platform.
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Turbulence vertical structure of the boundary layer during the afternoon transition
Atmospheric Chemistry and Physics, 2015Co-Authors: Clara Darbieu, Fabienne Lohou, Marie Lothon, J. Vilà-guerau De Arellano, Fleur Couvreux, Pierre Durand, David Pino, Edward G. Patton, Erik Nilsson, E. Blay-carrerasAbstract:Abstract. We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars and two aircraft during the afternoon transition. We analysed a case study based on some of these observations and large-Eddy simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence and (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to characterize the variation in the turbulent decay with height and study the distribution of turbulence over Eddy Size. This study highlights the LES ability to reproduce the turbulence evolution throughout the afternoon. LESs and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays at a low rate, with no significant change in turbulence characteristics, and (2) a second phase characterized by a larger TKE decay rate and a change in spectral shape, implying an evolution of Eddy Size distribution and energy cascade from low to high wave number. The changes observed either in TKE decay (during the first phase) or in the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.
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Turbulence vertical structure of the boundary layer during the afternoon transition
Atmospheric Chemistry and Physics Discussions, 2014Co-Authors: Clara Darbieu, Fabienne Lohou, Marie Lothon, Fleur Couvreux, Pierre Durand, David Pino, Erik Nilsson, J. Vilà-guerau De Arellano, E. G. Patton, E. Blay-carrerasAbstract:Abstract. We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars, and two aircraft flying extensively during the afternoon transition. We analyzed a case study based on some of those observations and Large-Eddy Simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence, (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to (1) characterize the variation of the turbulent decay with height and (2) study the distribution of turbulence over Eddy Size. This study points out the LES ability to reproduce the turbulence evolution throughout the afternoon. LES and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays with a low rate, with no significant change in turbulence characteristics, (2) a second phase characterized by a larger TKE decay rate and a change spectral shape, implying an evolution of Eddy Size distribution and energy cascade from low to high wavenumber. The changes observed either on TKE decay (during the first phase) or on the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.
Amilcare Porporato - One of the best experts on this subject based on the ideXlab platform.
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mean velocity profile in a sheared and thermally stratified atmospheric boundary layer
Physical Review Letters, 2011Co-Authors: Gabriel G Katul, Alexandra G Konings, Amilcare PorporatoAbstract:: A stability correction function φ(m)(ζ) that accounts for distortions to the logarithmic mean velocity profile (MVP) in the lower atmosphere caused by thermal stratification was proposed by Monin and Obukhov in the 1950s using dimensional analysis. Its universal character was established from many field experiments. However, theories that describe the canonical shape of φ(m)(ζ) are still lacking. A previous link between the spectrum of turbulence and the MVP is expanded here to include the effects of thermal stratification on the turbulent kinetic energy dissipation rate and Eddy-Size anisotropy. The resulting theory provides a novel explanation for the power-law exponents and coefficients already reported for φ(m)(ζ) from numerous field experiments.
David S.-k. Ting - One of the best experts on this subject based on the ideXlab platform.
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The importance of turbulence intensity, Eddy Size and flame Size in spark ignited, premixed flame growth
1997Co-Authors: David S.-k. Ting, M. D. CheckelAbstract:The effects of laminar burning velocity, turbulence intensity, flame Size and Eddy Size on the turbulent burning velocity of a premixed growing flame were experimentally separated in a 125 mm cubical chamber with lean methane-air mixtures spark ignited at 1 atm and 300 K. The turbulence was up to 2 m/s with 1 to 4 mm Taylor microscale. For the near unity Lewis number and near zero Markstein number mixture considered here, the turbulent buming velocity, S t , can be approximated as: S t = S l + C d (r/λ)u', where S l is the laminar buming velocity, r is the mean flame radius, λ is the Taylor microscale, u' is the root mean square (r.m.s.) turbulence intensity and C d is a constant of the order 0.02.
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Technical Note: The importance of turbulence intensity, Eddy Size and flame Size in spark ignited, premixed flame growth:
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 1997Co-Authors: David S.-k. Ting, M. D. CheckelAbstract:AbstractThe effects of laminar burning velocity, turbulence intensity, flame Size and Eddy Size on the turbulent burning velocity of a premixed growing flame were experimentally separated in a 125 mm cubical chamber with lean methane-air mixtures spark ignited at 1 atm and 300 K. The turbulence was up to 2 m/s with 1 to 4 mm Taylor microscale. For the near unity Lewis number and near zero Markstein number mixture considered here, the turbulent burning velocity, St, can be approximated as: St = Sl + Cd(r/λ)u′, where Sl is the laminar burning velocity, r is the mean flame radius, λ is the Taylor microscale, u′ is the root mean square (r.m.s.) turbulence intensity and Cd is a constant of the order 0.02.
Patrick Young - One of the best experts on this subject based on the ideXlab platform.
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turbulent convection in stellar interiors ii the velocity field
The Astrophysical Journal, 2009Co-Authors: David W Arnett, Casey Meakin, Patrick YoungAbstract:We analyze stellar convection with the aid of three-dimensional (3D) hydrodynamic simulations, introducing the turbulent cascade into our theoretical analysis. We devise closures of the Reynolds-decomposed mean field equations by simple physical modeling of the simulations (we relate temperature and density fluctuations via coefficients); the procedure (Convection Algorithm Based on Simulations) is terrestrially testable and is amenable to systematic improvement. We develop a turbulent kinetic energy equation which contains both nonlocal and time-dependent terms, and is appropriate if the convective transit time is shorter than the evolutionary timescale. The interpretation of mixing-length theory (MLT) as generally used in astrophysics is incorrect; MLT forces the mixing length to be an imposed constant. Direct tests show that the damping associated with the flow is that suggested by Kolmogorov (e K ≈ ρ(u')3 rms/l D , where l D is the Size of the largest Eddy and (u')rms is the local rms turbulent velocity). This Eddy Size is approximately the depth of the convection zone lCZ in our simulations, and corresponds in some respects to the mixing length of MLT. New terms involving the local heating due to turbulent dissipation should appear in the stellar evolutionary equations, and are not guaranteed to be negligible. The enthalpy flux (stellar "convective luminosity") is directly connected to the buoyant acceleration, and hence to the scale of convective velocity. MLT tends to systematically underestimate the velocity scale, which affects estimates of chromospheric and coronal heating, mass loss, and wave generation. Quantitative comparison with a variety of 3D simulations reveals a previously unrecognized consistency. Extension of this approach to deal with rotational shear and MHD is indicated. Examples of application to stellar evolution will be presented in subsequent papers in this series.
