LES of an axially excited non-circular bluff-body flame

This study focuses on multi-scale mixing processes in turbulent non-premixed hydrogen flames stabilised by conical non-circular (square, star) bluff-bodies. The research is carried out applying the large-eddy simulations (LES) with the help of commercial ANSYS software and an in-house code SAILOR based on a high-order compact difference algorithm for low Mach number reactive flows. First, we concentrate on the differences between non-circular bluff-body flames and the classical one stabilised by a circular bluff-body. In the latter case, the impact of a flat and corrugated wall on the flame dynamics is also considered. Downstream the non-circular bluff-bodies the mechanisms intensifying the mixing process are found to rely on the interaction of the variable scale vortices generated at their edges. Additionally, we concentrate on the flame dynamics when a low energetic axial excitation (forcing) introduced by a sinusoidal variation of an oxidiser stream with a different frequency is applied. It causes a sudden change in the axial temperature distribution and leads to a shortening of the flame. It turns out that the forcing effect is more pronounced in the configurations with the non-circular bluff-bodies. The temperature maximum along the centreline is reduced by approximately 120 K and its localisation is shifted upstream by 60% of the bluff-body equivalent diameter.