Are premixed turbulent stagnation flames equivalent to fully developed ones? A computational study

Abstract

Numerical simulations of planar, one-dimensional turbulent premixed flames and of back-to-back premixed flames stabilized in a hypothetical stagnating flow with frozen turbulence were performed using different combustion models to discuss the question entered in the title. Typical flamelet models with and without a submodel of pressure-driven (countergradient) transport and the Zimont model were used. Numerical results indicate that, due to the spatial nonuniformity of the mean unburned mixture flow, the basic characteristics of stagnation flames differ substantially from the corresponding characteristics of fully developed, planar, one-dimensional flames. In particular, the results computed with the flamelet models indicate that the possibilities to evaluate the speed and the thickness of the aforementioned fully developed flames by processing the data on flame speed, burning velocity, and mean flame brush thickness, measured in the corresponding stagnation flames, are questionable. Furthermore, the Zimont model, which cannot yield a fully developed flame in principle, predicts reasonably well the stationarity of stagnation turbulent premixed flames, their speed, burning velocity, thickness, and structure even when quite strong simplifications of the turbulence submodel are invoked. These results also indicate that substantial differences between the two types of premixed turbulent flames exist.