Investigation of a Turbulent Flame Speed Closure Approach for Premixed Flame Calculations

Abstract

A computational model for turbulent premixed gaseous combustion is investigated, where the combustion process is modelled in terms of a single transport equation for a reaction progress variable c. Turbulent closure of the source term of the progress variable is based on a model, where the turbulent flame speed is used in an extension to a field variable. In order to check the model, numerical results are compared with experimental data from a turbulent premixed V-shaped flame, where the conditions of the approaching turbulent flow and of the chemical processes have been varied separately. Regarding the simple structure of this model, it is found to predict the flame shape and flame width sufficiently well. Additionally, three other relations from the literature for the turbulent flame speed variable have been tested with in this approach, showing that experimentally determined flame speed relations have to be reduced in order to be used within this flame speed closure. Furthermore, the influence of the formal structure of the reaction term (¯ωc ∼ |∇¯c|) is compared with that of two other possible approaches (¯ωc ∼ ¯c · (1 − ¯c)/Ly, and ¯ωc ∼ min[(l − ¯c),¯c,γ]). While the experimental flame shape has straight boundaries, for the parabolic approach a concave bounded flame shape is found, if the length scale Ly is hold constant. This can be understood by analyzing the reaction rate integral across the flame brush.