Combustion and Flame 153 (2008) 442–464 www.elsevier.com/locate/combustflame A 2-D DNS investigation of extinction and reignition dynamics in nonpremixed flame–vortex interactions Rishikesh Venugopal, John Abraham ∗ Maurice J. Zucrow Laboratories, School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907-2088, USA Received 31 May 2007; received in revised form 15 October 2007; accepted 26 October 2007 Available online 16 January 2008 Abstract Two-dimensional (2-D) DNS investigations of extinction and reignition dynamics during interactions of laminar nonpremixed flames with counterrotating vortex pairs are performed. The length and velocity scales chosen for the vortices are representative of those in the near fields of high-Reynolds-number jets such as those occurring in Diesel engines. The governing equations are solved with sixth-order spatial discretization and fourth-order time integration. Chemistry is modeled as an irreversible single-step reaction. Local extinction along the symmetry axis, followed by reignition, is observed. The extinction is characterized by strong unsteady effects, which are captured well by 1-D transient diffusion flamelet libraries, provided the time-history of the instantaneous scalar dissipation rate is taken into account. On the other hand, reignition is essentially a 2-D phenomenon involving flame–flame interactions, which are favored for smaller vortices and increasing flame curvature. The effects of unsteadiness and curvature on extinction and reignition are carefully assessed through parametric studies involving a range of vortex and flame characteristics. The interaction outcomes are summarized on Reynolds–Damköhler number (Re–Da) diagrams, which show the combined effects of unsteadiness and curvature on extinction and reignition. The implications of the observed interaction outcomes for turbulent combustion modeling in the near fields of jet diffusion flames are discussed.  2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Flame–vortex interactions; Extinction; Reignition; Unsteadiness; Curvature 1. Introduction Nonpremixed turbulent flames are characterized by interactions between fluid mechanics and chem- istry. An important manifestation of these interactions is the coupling between the scalar dissipation rates and reaction rates [1]. If the local value of scalar dis- * Corresponding author. Fax: +1 (765) 494 5660. E-mail address: jabraham@ecn.purdue.edu (J. Abraham). sipation rate χ exceeds a certain critical value χ e , ex- tinction occurs. The extinguished regions can reignite through one or more mechanisms such as the propa- gation of edge-flames [2–5] and engulfment by a hot neighborhood [2,6]. Since χ is a highly fluctuating variable in turbulent nonpremixed flames [7], we may encounter repeated extinction and reignition events, which could significantly impact flame stability and pollutant emissions. In fact, recent direct numerical simulation (DNS) studies of turbulent jet diffusion flames [3,8] have shown that extinction and reignition are prevalent in the near field of the jet. 0010-2180/$ – see front matter  2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.combustflame.2007.10.021