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EFFECT OF TURBULENCE CHARACTERISTICS ON LOCAL FLAME STRUCTURE OF H2-AIR PREMIXED FLAMES

Yuzuru Nada
Department of Mechano-Aerospace Engineering, Tokyo Institute of Technology Ookayama, Meguro-ku, Tokyo 152-8552; Faculty of Risk and Crisis Management, Chiba Institute of Science 3 Shiomi-cho, Choshi-city, Chiba 288-0025, Japan

Mamoru Tanahashi
Department of Mechanical and Aerospace Engineering Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

Toshio Miyauchi
Dept. Mechanical and Aerospace Eng., Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan; Organization for the Strategic Coordination of Research and Intellectual Properties Meiji University 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, Japan

Resumo

Direct numerical simulations (DNS) of turbulent premixed flames are conducted to investigate effects of turbulence characteristics on the local flame structure. Detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent hydrogen-air reaction in turbulence. Numerical conditions of DNSs can be classified into wrinkled flamelets regime, corrugated flamelets regime and thin reaction zones near the boundary of Karlovitz number = 1.0 of turbulent combustion diagram. For all cases, the distribution of heat release rate shows three-dimensionally connected sheet-like feature, even though the heat release rate is highly fluctuating along the flame front. The heat release rate tends to increase at the flame fronts convex toward the burned side. For the turbulent premixed flames in corrugated flamelets regime, the handgrip structure is produced by the intrusion of the coherent fine scale eddy into the flame and the heat release rate in this structure increases up to 1.2 times of that of laminar flame. The mechanism of heat release rate increase in this structure is clarified by discussing the balance of elementary reactions. In the wrinkled flamelets regime, the spire-like structure of the flame front can be observed. These structure are created by the coherent fine scale eddies of turbulence. By identifying flame elements in turbulence, their statistical characteristics are also discussed.