DNS and Modeling of Flame-Generated Turbulence and Counter-Gradient Diffusion in Turbulent Premixed Flames
作者单位：CIRSE Nagoya University Furo-cho Chikusa-ku Nagoya 464-8603 Japan Department of Mechanical Engineering Nagaoka University of Technology Kamitomioka Nagaoka 940-2188
会议名称：《The Sixth World Congress on Computational Mechanics in Conjunction with the Second Asian-Pacific Congress on Computational MechanicsⅠ》
会议日期：2004年
学科分类：080704[工学-流体机械及工程] 08[工学] 0807[工学-动力工程及工程热物理]
摘 要：Turbulent premixed flames propagating in homogeneous isotropic turbulent flows were directly simulated with a single-step irreversible reaction. Simulations were made for three different density ratios: case H, high-density ratio of flame ρ/ρ=7.53, case M, middle-density ratio of flame ρ/ρ=5.00, and case L, low-density ratio of flame ρ/ρ=2.50, while U’/U was nearly equal to unity. By these simulations, we obtained databases of fully developed stationary turbulent flames. These databases were investigated by analyzing the transport equations for turbulent kinetic energy and turbulent scalar flux to study flame-generated turbulence and counter-gradient diffusion. It was found that turbulent fluctuations of all components, especially the streamwise component, were amplified in the flame brash, and that flame-generated turbulence increased for a larger density ratio of the flame. Analysis based on the Favre-averaged transport equation for turbulent kinetic energy showed that pressure related terms produced kinetic energy in the flame brash. On the other hand, the diffusion and dissipation term and velocity gradient term decreased kinetic energy. It was also proved that the counter-gradient diffusion dominated turbulent scalar flux in the flame region. The Favre-averaged transport equation for turbulent scalar flux was analyzed on the basis of DNS databases. It was shown that the mean pressure gradient term, the fluctuating pressure term and the velocity-reaction rate correlation term played important roles on the counter-gradient diffusion, while the mean velocity gradient term, the mean progress variable gradient term and dissipation terms suppressed it.