Mamoru Tanahashi

Effect of flow-geometry on turbulence-scalar interaction in premixed flames

Turbulent combustion of stoichiometric hydrogen-air mixture is simulated using direct numerical simulation methodology, employing complex chemical kinetics. Two flame configurations, freely propagating and V-flames stabilized behind a hot rod, are simulated. The results are analyzed to study the influence of flame configuration on the turbulence-scalar interaction, which is critical for the scalar gradient generation processes. The result suggests that this interaction process is not influenced by the flame configuration and the flame normal is found to align with the most extensive strain in the region of intense heat release. The combustion in the rod stabilized flame is found to be flamelet like in an average sense and the growth of flame-brush thickness with the downstream distance is represented well by Taylor theory of turbulent diffusion, when the flame-brushes are non-interacting. The thickness is observed to saturate when the flame-brushes interact, which is found to occur in the simulated rod st...

Flame and eddy structures in hydrogen–air turbulent jet premixed flame

Three-dimensional direct numerical simulation (DNS) of hydrogen–air turbulent plane jet premixed flames, which are composed of jet with unburnt mixture gas and surrounding burnt gas for flame holding, has been conducted for two cases of mean streamwise velocity of the jet, 100xa0m/s and 350xa0m/s. Fully-developed homogeneous isotropic turbulence is superimposed on the mean flow. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is considered. Eddy structures which have large-scale in space are produced for both cases, whereas the mechanism of the eddy formation depends on the inlet velocity. Although combustion condition of the present DNS with inlet velocity 100xa0m/s is classified into corrugated flamelets regime, unburnt mixture islands frequently appear behind the main flame body. The creation of these islands is closely related to the fine-scale eddies in the unburnt gas and the separated unburnt mixture contributes to increase of heat release rate and turbulent burning...

Flame Brush Structure of H2-Air Turbulent Premixed Flames at High Reynolds Numbers

Three-dimensional direct numerical simulations (DNSs) of turbulent premixed planar, jet and V flames of hydrogen-air mixture have been conducted to investigate the flame brush and the local flame structures at high Reynolds number turbulences. The detail kinetic mechanism including 12 reactive species and 27 elementary reactions was used to represent the hydrogen-air reaction. For planar flame, flame front is highly fluctuating, and multi-layer structure, multiply-folded flame front and unburned mixture island which lead to corresponding increase of the flame brush thickness can be observed. The flame brush thickness of the planar flame is relatively uniform along the flame front, and is about 2∼3 times the integral length scale (l), which is defined from an energy spectrum. For the jet and V flames, the flame brush thicknesses grow with the streamwise direction from about 0.5∼1 times the integral length scale (l) to about 2∼3 times the integral length scale (l) due to the highly fluctuating flame front at the downstream region.Copyright