Transition of Turbulent Premixed Flame Structure with Turbulence Reynolds Number and Damkohler Number
Various regimes of turbulent premixed combustion are identified by the turbulence Reynolds number and the Damkohler number. In the present study, attention is focused on the transition of the flame structure from a wrinkled laminar flame to a distributed reaction zone. Schlieren photographs were taken for the qualitative measurements of the transition of the flame structure and the time-resolved temperature measurements were made by using a fine-wire thermocouple. Laser tomography was applied to the fractal analysis of the wrinkled laminar flame front. It was confirmed experimentally that the transition from a wrinkled laminar flame to a distributed reaction zone is caused by an increase in Reynolds number or a decrease in Damkohler number. The wrinkled laminar flame can be represented by fractal surfaces with a fractal dimension and inner and outer cutoffs for the fractal behavior. In the distributed reaction zone, vortex stretching eradicates the non-uniformity of mean flow and creates a uniform turbulent flow field of isotropy through the cascade of turbulent energy transfer. In the transition regime, the turbulent premixed flame has characteristic features of both wrinkled laminar flame and distributed reaction zone.
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