Effects of Damkohler Number on Lean Premixed Jet Flames in Crossflow Using Direct Numerical Simulation

In the present work, lean premixed jet flames in crossflow were studied using direct numerical simulation to explore the effects of Damkohler numbers ($Da$Da) on turbulence and flame characteristics. The configuration is based on an experiment, where a jet of lean premixed ethylene-air mixtures ($\phi $phi = 0.6) was injected into a hot vitiated crossflow. The case with a higher and lower Da is denoted as case Da+ and case Da-, respectively. It was found that the turbulence is weakened around the reaction zone of case $Da + $Da+. In contrast, the turbulence of case $Da - $Da- is barely influenced by heat release. The vorticity dynamics are examined with the enstrophy transport equation budget terms, and the viscous dissipation term is the main sink for both cases. The windward and leeward flame branches of case $Da + $Da+ are dominated by auto-ignition and premixed flame propagation respectively, while the auto-ignition and flame propagation modes coexist on the leeward flame branch of case $Da - $Da-. The scalar gradient magnitude in the leeward branch is generally lower compared with the windward branch so that the flame is overall thicker. The normal strain rate is negative, which tends to enhance the scalar gradient, but it becomes positive on the leeward side of case $Da + $Da+, which is influenced by the alignment between the scalar gradient and the principal strain rates.