Sensitivity to the Presence of the Combustion Submodel for Large Eddy Simulation of Transient Premixed Flame–Vortex Interactions

Abstract

In this paper, the sensitivity of large eddy simulation (LES) to the presence of the combustion submodel was investigated for transient interactions between premixed flame fronts and toroidal vortex structures generated at the wake of a circular orifice. To this end, LES computations were run, with and without the combustion submodel, for two orifice diameters: 40 mm and 20 mm. Nonuniform unstructured grids with a cell characteristic length varying in the range of 0.5À1 mm were used. In going from the 40-mm orifice to the 20-mm orifice, both the size and velocity of the vortex increase, leading to a different regime of interaction with the flame: the vortex only wrinkles the flame front in the 40-mm case (wrinkled regime) and also disrupts the continuity of the front, giving rise to the formation of separate reaction zones (i.e., flame pockets that leave the main front), in the 20-mm case (breakthrough regime). It has been found that the impact of the combustion submodel on LES predictions is strongly dependent on the regime of interaction. Results for the 40-mm orifice are substantially the same, regardless of the presence of the combustion submodel. Conversely, at the wake of the 20-mm orifice, the intensity of the flameÀvortex interaction is such that the combustion submodel is strictly needed to reproduce both the qualitative (evolution of the pockets formed and their interaction with the main front) and quantitative (flame speed) characteristics of the flame propagation correctly.

Time-Resolved Particle Image Velocimetry of dynamic interactions between hydrogen-enriched methane/air premixed flames and toroidal vortex structures

“…As demonstrated for pure methane flames [21][22][23][24], such simple and controllable vortex structures provide different benefits over truly turbulent fields when fundamental investigation into flameturbulence interactions is performed.…”

Flame acceleration in pipes containing bends of different angles

“…This is mainly due to the difference of calculation method of flame speed.Similar results have been observed in pipes with installed obstacles. The flame speed demonstrated the same trend with the steps of the flame acceleration past the orifice, deceleration (due to the flame expansion) and re-acceleration (due to the flame interaction with the combustion-generated turbulent flow field) (DiSarli et al, 2010;Di Sarli et al, 2012a;Di Sarli and Di Benedetto, 2011). The bend can also lead to flame expansion and turbulent flow.…”

“…Many researchers have studied accelerating flames in pipelines, tubes, ducts and other industrial processes (Bauwens et al, 2007;Ciccarell and Dorofeev, 2008;Di Sarli et al, 2012a;Di Sarli et al, 2012b;Di Sarli and Di Benedetto, 2011;Jr. Zipf et al, 2013;Jr.…”

Different combustion modes caused by flame-shock interactions in a confined chamber with a perforated plate

“…The present result is in line with the Bychkov theory [25] on flame acceleration mechanism over obstacles. Moreover, Benedetto et al [28][29][30] used time-resolved particle image velocimetry (TRPIV) and large eddy simulation (LES) to investigate the unsteady flame propagation around toroidal vortices generated at the wake of a circular orifice. Their simulation results showed the trend of flame propagation.…”

“…In fact, the flame acceleration and propagation are also the most important stages in the interaction between the flame and shock wave for understanding pressure oscillations. A great deal of effort [25,[28][29][30][31][32] has been spent on studying the turbulent flame acceleration mechanism in channels equipped with and without obstacles in past decades. These studies are focused on the stage of flame acceleration governed by flame-shock interaction which is an efficient way of increasing the flame energy release rate to form the detonation.…”