Modelling of flammable fuels in small and large scale turbulent environments

Abstract

This paper presents a mathematical modelling analysis of two propagating flames inside small and large enclosures of different geometrical configurations via computational fluid dynamics. Fuels considered are hydrogen and methane respectively. As the reactivity of the two fuels vary, time histories of over-pressure and flame position vary accordingly. The level of turbulence produced due to impinging the propagating flame with obstructions drives the location of flow amongst the combustion regime diagram and thus controls the validity of combustion models used. In the present study, the large eddy simulation (LES) technique as fitted in ANSYS Fluent is employed. The turbulent flame speed closure (TFC) is selected with revisiting the validity of its standard formulation. As the interaction of the propagating flame with obstructing walls is considered to be a key feature on determining the turbulence levels attained, it was sought to compare two models, namely the Dynamic Smagorinsky-Lilly and WALE models. Despite the fact that small scale experimental facilities are more adequate for producing detailed diagnostics of the deflagration scenario experimentally as well as allowing LES analysis with a reasonable mesh size within computational economy, it was recognized that the terminal objective is to evaluate the level of performance when dealing with large scale cases. The agreement between the predictions and set of experimental measurements used suggests a reasonable level of qualitative agreement for all different cases, providing a better understanding of models used to simulate the phenomena involved with discrepancies spotting light on areas of potential future improvements.