LES of the Cambridge Stratified Swirl Burner using a Sub-grid pdf Approach

Abstract

The sub-grid scale probability density function equation is rearranged in order to separate the resolved and sub-grid-scale (sgs) contributions to the sgs mixing term. This allows modelling that is consistent with the limiting case of negligible sub-grid scale variations, a property required for applications to laboratory premixed flames. The new method is applied to the Cambridge Stratified Swirl Burner for 6 operating conditions, 2 isothermal and 4 burning, with varying degrees of swirl and mixture stratification. The simulations are performed with the Large Eddy Simulation (LES) code BOFFIN in which the modelled pdf transport equation is solved using the Eulerian stochastic field method. Eight stochastic fields are used to account for the influence of the sub-grid fluctuations and the chemistry is modelled with a reduced version of the GRI 3.0 mechanism for methane involving 19 species and 15 reaction steps. The simulated velocities for both the isothermal and burning cases show good agreement with the experimental data. The measured temperature and major species profiles are also reproduced to a good accuracy.

Comparison of VLES and LES Turbulence Modeling for Swirling Turbulent Flow

“…Thus the mesh with 3.2 million cells is finally selected. The computational grids are comparable to those in previous LES studies (Brauner, et al 2016) of the same swirling case.…”

Assessing the Effect of Differential Diffusion for Stratified Lean Premixed Turbulent Flames with the Use of LES-PDF Framework

“…This pdf can be used to describe the behaviour of scalars on the sub-filter level by essentially describing the probability of φ = ψ arising inside a filter volume, thus providing the information necessary to evaluate the filtered chemical source term. Following the approach of [36,27] the resolved part of the sub-grid 'mixing' term is subtracted from both sides of the equation and so that the resulting pdf evolution equation can be written:…”

Large Eddy Simulation of Premixed Stratified Swirling Flame Using the Finite Rate Chemistry Approach

“…In the present work, the 2-step global mechanism for methane oxidation is selected to handle the combustion and the chemical reactions are formulated as equations (15) and (16). Two sets of Arrhenius parameters are adopted to describe the chemical kinetics, one for the 2sCM2 scheme [37] (referred to as Mech I) and the other for the Arrhenius parameter-optimized 2-step scheme (referred to as Mech II) reduced based on the GRI 3.0.…”

“…The mesh is refined near the bluff body and shear layers, which generates a corresponding minimal mesh space of 0.4 mm and overall cell number of about 1.6 million. The minimum grid spacing in the vicinity of the burner exit is considered a reasonable size to resolve the turbulence in the reacting zone [15]. The OpenFOAM reacting-Foam solver is employed in the large eddy simulation of reaction cases, which is an unsteady reactive flow solver, and the thermophysical model for reacting mixture is based on compressibility ψ = RT −1 .…”

“…Proch and Kempf [14] simulated three stratified nonswirling cases using the artificial thickened flame (ATF) approach in combination with flamelet-generated manifold (FGM) lookup tables, and the process of stratified combustion was characterized and investigated from simulation results. Brauner et al [15] simulated six SwB cases with varying degrees of swirl and mixture stratification by using the LES-PDF method with the Eulerian stochastic field solution method. Velocity and major species profiles showed good agreement with experimental data, whilst local temperature profiles had slight discrepancies in the central regions for swirling cases.…”