TY - JOUR
T1 - Statistics of local and global flame speed and structure for highly turbulent H2/air premixed flames
AU - Song, Wonsik
AU - Hernandez Perez, Francisco
AU - Tingas, Alexandros
AU - Im, Hong G.
N1 - KAUST Repository Item: Exported on 2021-08-06
Acknowledgements: This work was sponsored by King Abdullah University of Science and Technology (KAUST). Computational resources were provided by the KAUST Supercomputing Laboratory (KSL). The work of EAT was also supported by the Royal Society of Edinburgh (RSE) through the RSE/Scottish Government Sabbatical Research Grant scheme with grant no. 64676.
PY - 2021/6/27
Y1 - 2021/6/27
N2 - A statistical analysis is conducted for turbulent hydrogen-air premixed flames at a range of Karlovitz numbers up to 1,126 by direct numerical simulations (DNS) with detailed chemistry. The local and global burning velocities are evaluated and the deviation from the laminar flame speed is assessed. It is found that the global turbulent flame speed is largely determined by the integral length scale than the turbulent Karlovitz number, due to the flame surface area enhancement. The turbulent flame speed in all examined cases correlates well with the flame surface area, according to Damköhler's first hypothesis; even at Karlovitz number well above 1,000, reaction zones stay intact and only the preheat zone is broadened by the strong turbulence level. The statistical analysis with the probability density function (PDF) for the displacement speed shows that the highest probability of the local flame speed coincides with the one-dimensional unstretched flame speed. Despite some deviations, the mean flame structures and reaction rate of hydrogen of the higher Ka cases are found to resemble those of the laminar flame, and this further confirms that the turbulent flame brush topology is mainly determined by the large scale turbulence behavior. The results also suggest that the engineering modeling based on the flamelet concept may be valid for a wider range of Ka conditions.
AB - A statistical analysis is conducted for turbulent hydrogen-air premixed flames at a range of Karlovitz numbers up to 1,126 by direct numerical simulations (DNS) with detailed chemistry. The local and global burning velocities are evaluated and the deviation from the laminar flame speed is assessed. It is found that the global turbulent flame speed is largely determined by the integral length scale than the turbulent Karlovitz number, due to the flame surface area enhancement. The turbulent flame speed in all examined cases correlates well with the flame surface area, according to Damköhler's first hypothesis; even at Karlovitz number well above 1,000, reaction zones stay intact and only the preheat zone is broadened by the strong turbulence level. The statistical analysis with the probability density function (PDF) for the displacement speed shows that the highest probability of the local flame speed coincides with the one-dimensional unstretched flame speed. Despite some deviations, the mean flame structures and reaction rate of hydrogen of the higher Ka cases are found to resemble those of the laminar flame, and this further confirms that the turbulent flame brush topology is mainly determined by the large scale turbulence behavior. The results also suggest that the engineering modeling based on the flamelet concept may be valid for a wider range of Ka conditions.
UR - http://hdl.handle.net/10754/670436
UR - https://linkinghub.elsevier.com/retrieve/pii/S0010218021002662
UR - http://www.scopus.com/inward/record.url?scp=85111062109&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2021.111523
DO - 10.1016/j.combustflame.2021.111523
M3 - Article
SN - 1556-2921
VL - 232
SP - 111523
JO - Combustion and Flame
JF - Combustion and Flame
ER -