Numerical analysis of influence of various bluff-body shapes on diffusion flame dynamics

Abstract

Abstract In this paper, various bluff-body shapes (cylindrical, square, star) and two different surface topologies (smooth, wavy) are applied as passive tools for controlling a non-premixed hydrogen flame in a combustion chamber. We focus on the dynamics of the flame and its time-averaged characteristics in the close vicinity of an injection system within formed recirculation zones and also in a far-field. The research is performed with the help of large-eddy simulations (LES) method using the ANSYS Fluent software and a high-order academic code SAILOR. Flame behaviour is found to be strongly dependent on the geometry of the bluff-body whereas its wall topology affects the flame characteristics only slightly. In the cases with the square and star bluff-body, small vortical structures originating at the corners deform large vortical structures created by the Kelvin-Helmholtz instability mechanism. This intensifies the mixing and combustion process and, in the configuration with the square shape bluff-body, translates to the shortening of the recirculation zone by 15% of the equivalent bluff-body diameter and the flame, which in the axis develops closer to the bluff-body. The star shape leads to the most uniform flame at the radial border or the recirculation zone.