Large-eddy / Reynolds-Averaged Navier-Stokes Simulation of Cavity-Stabilized Ethylene Combustion

摘要

In this study, a hybrid large-eddy / Reynolds-averaged Navier-Stokes method is used to simulate ethylene combustion inside a cavity flameholder. The cavity flameholder considered is Configuration E of University of Virginia's scramjet combustion facility, which consists of a Mach 2 inlet nozzle, a constant-area isolator, a combustor, and an extender, through which the exhaust gases are vented to the atmosphere. To increase the fuel-residence time, a cavity is fitted along the upper wall inside the combustor section of the flameholder. The configuration has the capability of injecting ethylene through a series of ports located upstream of and inside the cavity along the upper wall the combustor. In the simulations, ethylene combustion is modeled using a 22-species ethylene oxidation mechanism. Also, a synthetic eddy method is used to introduce turbulence at the inflow plane of the flameholder. For an equivalence ratio of 0.15, a cavity stabilized flame is predicted. Results predicted compare well with the experimental data, especially, water mole-fraction distribution and pressure along the upper wall of the combustor. In general, the predictions show excellent agreement with experimental data within the cavity region; further downstream, experimental results suggest that the heat release is over-predicted in the simulations. Analysis of the flame structure predicted by the LES/RANS method indicates that the flame propagates into a stoichiometric to fuel-rich mixture near the cavity. Flame angles captured in the simulation are in close agreement with those predicted through classical premixed turbulent flame-speed estimates. Further downstream, the flame structure is non-premixed in character, and near complete conversion of CO to CO2 is observed by the time the flame reaches the combustor exit.