@article{echekki_kolera-gokula_2007, title={A regime diagram for premixed flame kernel-vortex interactions}, volume={19}, ISSN={["1089-7666"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34248171898&partnerID=MN8TOARS}, DOI={10.1063/1.2720595}, abstractNote={Direct numerical simulations of flame kernel-vortex interactions are implemented in an axisymmetric configuration using a two-step global mechanism to study the different combustion regimes of the interactions. Four combustion regimes have been identified. They include: (1) the “laminar kernel” regime, (2) the “wrinkled kernel” regime, (3) the “breakthrough” regime, and (4) the “global extinction” regime. Transitions from different regimes are achieved through variations of the vortex strength, and operation in each regime is governed by two key parameters, the ratio of the vortex translational velocity to the laminar flame speed and the ratio of the kernel size to the vortex size at the onset of the interactions. Qualitative and quantitative comparisons between the flame responses in the different regimes are presented. A regime diagram is constructed based on the key parameters that control transition between the different regimes. The diagram bears some similarities with other diagrams based on planar flame-vortex interactions. However, it also offers additional features that constitute refinements to the existing diagrams of which the role of interaction of a vortex with an already curved flame is important.}, number={4}, journal={PHYSICS OF FLUIDS}, author={Echekki, Tarek and Kolera-Gokula, Hemanth}, year={2007}, month={Apr} }
 @article{kolera-gokula_echekki_2007, title={The mechanism of unsteady downstream interactions of premixed hydrogen-air flames}, volume={179}, ISSN={["1563-521X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34848833545&partnerID=MN8TOARS}, DOI={10.1080/00102200701484191}, abstractNote={Abstract The process of flame annihilation resulting from downstream interactions of premixed hydrogen-air flames is studied using Direct Numerical Simulations (DNS). The process is investigated during unsteady interaction between a vortex pair and a premixed flame kernel in 2D. The annihilation process results from the interactions of the premixed flames on their products' side. The simulations show that the mechanism of extinction during downstream interaction is different from an upstream interaction, which is governed by the sequence of the interactions of the different preheat and reaction layers on both processes and the diffusive transport of heat and mass. In contrast to observations related to upstream interactions, downstream interactions lead to a shift in the equivalence ratio towards the richer conditions with a steady decrease in chemical activity and no radical pool build-up during the stages of extinction. The effect of vortex sizes is qualitatively the same between the different cases considered.}, number={11}, journal={COMBUSTION SCIENCE AND TECHNOLOGY}, author={Kolera-Gokula, Hemanth and Echekki, Tarek}, year={2007}, pages={2309–2334} }
 @article{kolera-gokula_echekki_2006, title={Direct numerical simulation of premixed flame kernel-vortex interactions in hydrogen-air mixtures}, volume={146}, ISSN={["1556-2921"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33745213127&partnerID=MN8TOARS}, DOI={10.1016/j.combustflame.2006.04.002}, abstractNote={Abstract The unsteady interaction between a vortex pair and a premixed flame kernel in 2D is investigated numerically using direct numerical simulations with a detailed reaction mechanism for hydrogen chemistry. The simulations are based on variations of the vortex size and strength with respect to a base case and in comparison with an unperturbed premixed flame kernel. The simulations result in two different regimes for flame kernel–vortex interactions, which, based on the parameter range considered, are consistent with experimental observations. The first regime, the global extinction regime, is characterized by an interaction that is initiated when the kernel is still small compared to the vortex pair core size. The second regime corresponds to an interaction later in time when the kernel size is larger than the vortex pair core size, which results primarily in a wrinkling effect on the flame kernel. Computations of different global quantities show that the vortex-pair causes an enhancement in the flame surface area and the volumetric fuel consumption rate in the break through regime. However, there is a reduction in the global consumption speed during the interaction associated with the effect of stretch on flame structure. A rescaling of the time scale, taking into consideration the vortex-pair translational velocity, is derived, which represents the main effect of the vortex-induced stretch on the flame surface area. Moreover, a new parameter is derived to evaluate the fraction of mutually interacting flames. Downstream interactions, which correspond to the proximity of flames from their burned gas side, are the dominant contribution to flame–flame interactions.}, number={1-2}, journal={COMBUSTION AND FLAME}, author={Kolera-Gokula, Hemanth and Echekki, Tarek}, year={2006}, month={Jul}, pages={155–167} }