Numerical study of the characteristics of turbulent premixed flames

Turbulent premixed flames are present in a wide range of applications. The nature of these flames transitioning from initially quasi-laminar to fully turbulent results in difficulty when providing numerical predictions. The presence of obstructions in the path of the premixed flame further deforms the transient flame front and amplifies the severity of the event. Large eddy simulations (LES) techniques are applied for simulations in this study to investigate turbulent premixed combustion. The LES technique continues to evolve as a prevailing numerical tool for the modelling of unsteady flame propagation. The challenge of applying LES for predictions of turbulent premixed flames is in part due to difficulty modelling the thin transient flame front. Results presented in this thesis apply a dynamic flame surface density (DFSD) model for estimations of the filtered reaction rate. Model parameters are automatically calculated based on the resolved flame front characteristics.

The LES-DFSD model is applied to examine turbulent premixed flame propagation past consecutive solid obstructions in a lab-scale combustion chamber. Numerical results presented in this thesis focus on model predictions for hydrogen-air mixtures and obstacle configurations using multiple reported experimental test cases. Sensitivity of numerical results to parameters such as grid resolution and filter width are also inspected. The novelty of this research is within investigating hydrogen flame interaction with obstructions of varied area blockage ratios (ABRs). The numerical model is found to be successful in reproducing published experimental data. Numerical results for key combustion events such as the maximum rate of pressure rise, peak overpressure and flame speed well represent experimental data. Further, the LES-DFSD model replicates the transient flame structure observed in experimental images. The effect of obstruction ABR as well as baffle location and frequency is investigated. A brief comparison between hydrogen and propane mixtures finds that hydrogen flames generated greater overpressures at higher flame speeds when compared with propane.