Numerical Control of 3D Turbulent Premixed Flame Simulations

One of the well-known properties of turbulent, premixed flames is that their speed of propagtion is correlated to the intensity of the turbulence they encounter. A simple consequence is that these types of flames are inherently unstable. Given a source of turbulence, if the flame is propagating faster than the mean flow, it will drift upstream and encounter increased turbulent intensities that further accelerate the flame in the upstream direction. There will be an analogous deceleration if the flame speed is slower than the mean flow. To address this instability, experimental studies of premixed flames impose mean flow conditions faster than the turbulent flame speed and introduce some type of geometric or aerodynamic stabilization. Examples of these types of stabilized flames are V-flames, bluff-body flames, Bunsen flames, stagnation flames and swirl-stabilized flames. These types of flames are all the subject of active research in the experimental community (see the 29 Proceedings of the Combustion Institute). Each of these configurations introduces its own particular features. For example, in stagnation flames there is a strong mean strain, in a bluff-body flame there is a larger recirculation zone, etc. The impact of the stabilization on flame properties introduces an additional complexity into the study of premixed turbulent combustion. The inherent instability of turbulent, premixed flames also introduces problems for computational studies. One possibility is to attempt to include the flame stabilization mechanism in an overall reacting flow simulation. Thus approach has been pursued by Bell et al. [3] but the associated computational costs make this prohibitive for performing detailed parametric studies. A popular alternative configuration employed in direct numerical simulations (DNS) involves a doubly-periodic box domain with inlet and outflow boundaries in the direction of the mean flow. A 1D steady solution is used to initialize a flame and turbulent fluctuations are superimposed on the inlet flow. Such three-dimensional configurations were first studied by Trouvé and Poinsot [7] and by Zhang and Rutland [8] for simplified chemistry. More recently Tanahashi et al. [5, 6] have performed simulations of this type for turbulent, premixed hydrogen flames with detailed hydrogen chemistry. Bell et al. [1] performed a similar study for a turbulent methane flame. Unfortunately, due to the turbulent flame instabilities discussed above, the resulting flames are either accelerating or decelerating, and therefore encountering a time-varying turbulent intensity. Bell et al. [2] introduce a feedback control algorithm for two-dimensional flows that automatically stabilizes a 2D ”turbulent” flame in a configuration analogous to the DNS setting described above by dynamically adjusting the mean inflow velocity condition. This algorithm produces a statistically stationary, stable configuration where turbulence properties