Application of a Coherent Flame Model to Premixed Turbulent Combustion Impinging on a Wall

Abstract

A coherent flame model is applied to analyse premixed turbulent flames stabilised in a stagnation flow impinging on a wall. Because flames which are well separated from the wall are investigated here, interaction between the turbulent wrinkled flame and the wall is assumed to be insignificant. In view of this assumption a mean reaction rate model which was previously used in a counterflow geometry is adopted to solve the present problem. Therefore, a model parameter, β, describing annihilation between flame surfaces, is given the same value as that found in corresponding back-to-back premixed turbulent counterflow flames. Non-reactive outer and reactive inner regions in the flow are also found and described by a composite solution for these two regions, with an allowance for the displacement thickness of the thermal boundary layer next to the wall. Boundary layer analysis based on a modified κtilde;-ϵtilde; model is also adopted to resolve the effect of the wall on the evolution of turbulent motion. The thermal boundary layer is found to be thick and slightly overlaps the flame brush. However, the effective displacement thickness of the thermal boundary layer is found to be small in comparison with the separation between the nozzle exit and the plate. The present solutions for the boundary layer analysis are related to an equivalent non-reactive hot flow impinging on the wall. Thus, a limited amount of experimental data from stagnating cold flows can be used to compare predicted heat transfer rates. Generally the predictions give satisfactory agreement with experiments.

Notes

The present address: Chung Shun Institute of Science and Technology, Lung Tan P.O. 90008-15-1 Taiwan, 32526, R.O.C.