A dominant factor in determining the burning rate of a premixed turbulent flame is the degree to which the flame front is wrinkled by turbulence. Higher turbulent intensities lead to greater wrinkling of the flame front and an increase in the turbulent burning rate. This picture of turbulent flame dynamics must be modified, however, to accommodate the affects of variations in the local propagation speed of the flame front. Classical flame analysis characterizes these local variations in propagation speed by the Markstein number which represents the response of the flame front to curvature and strain. In this paper, we consider lean premixed flames for three different fuels having widely varying fuel Lewis numbers corresponding to widely varying Markstein numbers. In particular, we present numerical simulations of premixed turbulent flames for lean hydrogen, propane and methane mixtures in two dimensions. Each simulation is performed at turbulence conditions similar to those found in laboratory-scale experiments and is performed using detailed chemical kinetics and transport properties. We discuss the effect of Lewis number on the overall flame morphology and explore the dependence of local flame propagation speed on flame curvature. We also explore the relationship between local flame speed and experimentally accessible variables such as OH concentration. Finally, we focus on the low Lewis number case, hydrogen, in which the flame front is broken indicating local extinction.
We present a three-dimensional, time-dependent simulation of a laboratory-scale rod-stabilized premixed turbulent V-flame. The experimental parameters correspond to a turbulent Reynolds number, Re t ؍ 40, and to a Damkö hler number, Da ؍ 6. The simulations are performed using an adaptive time-dependent low-Machnumber model with detailed chemical kinetics and a mixture model for differential species diffusion. The algorithm is based on a second-order projection formulation and does not require an explicit subgrid model for turbulence or turbulence͞chemistry interaction. Adaptive mesh refinement is used to dynamically resolve the flame and turbulent structures. Here, we briefly discuss the numerical procedure and present detailed comparisons with experimental measurements showing that the computation is able to accurately capture the basic flame morphology and associated mean velocity field. Finally, we discuss key issues that arise in performing these types of simulations and the implications of these issues for using computation to form a bridge between turbulent flame experiments and basic combustion chemistry. (6)] have made substantial progress in understanding basic flame physics and developing models that can be used for engineering design. However, the inability of theory to deal with the complexity of realistic chemical kinetics in a turbulent flowfield, and the present limitations in experimental diagnostics to resolve 3D flame properties, represent major obstacles to continued progress.Numerical simulation offers the potential to augment theory and experiment and overcome the limitations of standard approaches in analyzing laboratory-scale flames. The excessive computational costs of incorporating detailed transport and chemical kinetics have necessitated compromises in the fidelity or scope of simulations for premixed turbulent combustion. Simulation of laboratory-scale systems typically involves models for subgrid-scale turbulent fluctuations. Approaches based on large eddy simulation or Reynolds-averaged Navier-Stokes fall into this class. In addition to the turbulence model, these approaches require a model for the speed of flame propagation in a turbulent field or some other model for turbulencechemistry interaction.The goal of the present work is to simulate a laboratory-scale flame, Ϸ10-12 cm in length, without a turbulence model, a burning velocity model, or the introduction of some other type of turbulence closure hypothesis. Standard computational tools for this type of simulation are based on high-order (more than four) explicit integration methods for the compressible NavierStokes equations and are typically referred to as direct numerical simulations. The computational requirements of direct numerical simulations have limited most simulations to small-scale 2D models. Recent work by Vervisch et al. (7) presents the simulation of a laboratory-scale ''turbulent'' premixed V-flame in two dimensions and represents the current state-of-the-art in 2D direct numerical simulations. Tanahashi e...
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