Network topology of turbulent premixed Bunsen flame at elevated pressure and turbulence intensity

For turbulent premixed flame surface, folded regions will be formed mainly depending on the turbulence-flame interaction and are significant structures which can increase flame surface area at large scale and enhance the local displacement speed. The conventional methods, such as PDF distribution of curvature, may not properly label the folded regions of turbulent flame because these regions intrude deeply into the products, resulting in a small curvature probability. This problem may be aggravated at elevated pressure and turbulence intensity conditions when more folded regions appear at the turbulent flame front. To identify the folded regions, Network topology of turbulent premixed flame front is constructed using the "visibility" method. Results show that this method can convert the spatial signal of turbulent flame to network topology, labeling the folded regions. Compared with curvature PDF, node degree distribution of network can reflect the mechanism of turbulence-flame interaction when the non-dimensional turbulence intensity is increased by different ways. The network structure of turbulent flame will transfer from sparse to condense when the dimensionless turbulence intensity is increased by pressure and perforated plate, as these two methods will extend the turbulence-flame interaction time and promote the interaction intensity, respectively. However, although the dimensionless turbulence intensity will increase with the augment of outlet velocity, the node degree distribution of network structure of turbulent flame front keeps almost constant. This is caused by the reduced turbulence-flame interaction time. It suggests that the turbulence-flame interaction time is an factor as important as the dimensionless turbulence intensity in turbulent premixed combustion. For forced-turbulent premixed flame at elevated turbulence intensity, the "bending phenomenon" will be hidden if the outlet velocity is not taken into account, as the outlet velocity is related to the turbulence-flame interaction time. (C) 2019 Elsevier Masson SAS. All rights reserved.