Unsteady simulation of a CO/H₂/N₂/air turbulent non-premixed flame

Abstract

The Sandia/ETH-Zurich CO/H 2 /N 2 non-premixed unconfined turbulent jet flame (named 'Flame A') is numerically simulated by solving the unsteady compressible reactive NavierStokes equations in a three-dimensional axisymmetric formulation, hence, in a formally twodimensional domain. The turbulent combustion closure model adopted is the Fractal Model, FM, developed as a subgrid scale model for Large Eddy Simulation. The fuel is injected from a straight circular tube and the corresponding Reynolds number is 16 700, while the air coflows. Since the thickness of the nozzle is 0.88 mm, and the injection velocity high, ∼104 m s −1 , capturing the stabilization mechanism of the actual flame requires high spatial resolution close to the injector. Results are first obtained on a coarse grid assuming a fast-chemistry approach for hydrogen oxidation and a single step mechanism for carbon monoxide oxidation. With this approach the flame is inevitably anchored. Then, to understand the actual flame stabilization a more complex chemical mechanism, including main radical species, is adopted. Since using this chemistry and the coarse grid of previous simulation the flame blows off numerically, attention is focused on understanding the actual flame stabilization mechanism by simulating a small spatial region close to the injection with a very fine grid. Then, analysing these results, an artificial anchoring mechanism is developed to be used in simulations of the whole flame with a coarse grid. Unsteady characteristics are shown and some averaged radial profiles for temperature and species are compared with experimental data.

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H2Combustion

“…The SLF model (with a steady flamelet library of 20 different flamelets and different strain rates up to 1000 s −1 ) overpredicted the axial temperature profile, especially in the post-flame zone. Giacomazzi et al (2008) also performed axisymmetric simulations (of flame A) but using large eddy simulation (LES). They adopted the fractal model (FM) as a subgrid scale model.…”

Investigation of flame surface density modeling for large eddy simulation of turbulent premixed flames by comparison with a prescribed reference solution

“…Equations (13 -14) are now closed requiring solutions given by known expressions. We assume that the flame behave as a fractal surface at all stages of its development [23,28,49,[54][55][56][57][58][59][60][61][62][63][64][65]:…”

“…In the following, we assume that the flame behaves as a fractal surface at all stages of its development, as suggested by various models and analysis [23,28,49,[54][55][56][57][58][59][60][61][62][63][64][65]. Once derived the balance equations describing the evolution of a statistically one-dimensional flame evolving in an homogenous and isotropic frozen turbulence (Section 2), exact closures are proposed to fit this requirement (Section 3) while the influence of two sub-grid scale models, a simple algebraic model and its dynamic version, on resolved and total flame surfaces, and then on the overall turbulent flame speed, as well as the unsteady flame response, are discussed in Section 4, including model parameter uncertainties.…”

Large Eddy Simulation of a Syngas Jet Flame: Effects of Preferential Diffusion and Turbulence–Chemistry Interaction

“…Conversely, some previous studies have noted the influence of nonunity Lewis numbers. Giacomazzi et al , simulated a turbulent syngas jet flame considering nonunity Lewis numbers and reported that preferential mass diffusion of H 2 controlled flame stabilization near the nozzle. Meier et al also suggested that preferential mass diffusion played an important role, especially near the nozzle.…”