A flame particle tracking analysis of turbulence-chemistry interaction in hydrogen-air premixed flames

详细信息    查看全文

• 作者：Harshavardhana A. Uranakara^a ; Swetaprovo Chaudhuri^a ; ^b ; ^{schaudhuri@aero.iisc.ernet.in" class="auth_mail" title="E-mail the corresponding author} ; ^{swetaprovo@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Himanshu L. Dave^a ; Paul G. Arias^c ; Hong G. Im^c
• 关键词：Direct numerical simulation ; Turbulent premixed flames ; Displacement flame speed ; Flame particle tracking
• 刊名：Combustion and Flame
• 出版年：2016
• 出版时间：January 2016
• 年：2016
• 卷：163
• 期：Complete
• 页码：220-240
• 全文大小：14231 K

文摘

Interactions of turbulence, molecular transport, and energy transport, coupled with chemistry play a crucial role in the evolution of flame surface geometry, propagation, annihilation, and local extinction/re-ignition characteristics of intensely turbulent premixed flames. This study seeks to understand how these interactions affect flame surface annihilation of lean hydrogen–air premixed turbulent flames. Direct numerical simulations (DNSs) are conducted at different parametric conditions with a detailed reaction mechanism and transport properties for hydrogen–air flames. Flame particle tracking (FPT) technique is used to follow specific flame surface segments. An analytical expression for the local displacement flame speed (S_d) of a temperature isosurface is considered, and the contributions of transport, chemistry, and kinematics on the displacement flame speed at different turbulence-flame interaction conditions are identified. In general, the displacement flame speed for the flame particles is found to increase with time for all conditions considered. This is because, eventually all flame surfaces and their resident flame particles approach annihilation by reactant island formation at the end of stretching and folding processes induced by turbulence. Statistics of principal curvature evolving in time, obtained using FPT, suggest that these islands are ellipsoidal on average enclosing fresh reactants. Further examinations show that the increase in S_d is caused by the increased negative curvature of the flame surface and eventual homogenization of temperature gradients as these reactant islands shrink due to flame propagation and turbulent mixing. Finally, the evolution of the normalized, averaged, displacement flame speed vs. stretch Karlovitz number are found to collapse on a narrow band, suggesting that a unified description of flame speed dependence on stretch rate may be possible in the Lagrangian description.