The Eulerian Stochastic Fields Method Applied to Large Eddy Simulations of a Piloted Flame with Inhomogeneous Inlet

Abstract

Large Eddy Simulations of the Sydney mixed-mode flame with inhomogeneous inlet (FJ200-5GP-Lr75-57) are performed using the Eulerian Stochastic Fields (ESF) transported probability functions method to account for the sub-grid scale turbulence–chemistry interaction, to demonstrate the suitability of the ESF method for mixed-mode combustion. An analytically reduced 19-species methane mechanism is used for the description of the chemical reactions. Prior to the reactive case, simulation results of the non-reactive setup with cold and hot pilot stream are presented, which show differences in the jet breakup and radial species mass fluxes. The reactive case simulations are compared to experimental data and a recently conducted model free quasi-DNS (qDNS), showing very good agreement with the qDNS in terms of scatter data and radial mean values of temperature and species distribution, as well as mixture fraction conditional statistics. Further analysis is dedicated to sub-grid scale statistics, showing that mixture fraction and reaction progress variable are strongly correlated in this flame. The impact of the number of stochastic fields on the filtered temperature and species distribution is investigated; it reveals that the ESF method in conjunction with finite-rate chemistry is very insensitive to the number of employed fields to obtain highly accurate simulation results.

Identification of Flame Regimes in Partially Premixed Combustion from a Quasi-DNS Dataset

“…Luo et al (2020) applied a dynamic second-order moment closure model to LES and found that the premixed flame is dominant upstream, causing 70 % of the heat release, which then decreases to about 40 % downstream, with an overall good agreement with measurements. Hansinger et al (2020) performed LES with the Eulerian Stochastic Fields Method and assessed the influence of the number of stochastic fields on the quality of the simulation results. Shrotriya et al (2020) conducted LES with reaction diffusion manifolds (REDIM) because it is mostly independent of the combustion regime.…”

Validation of an Eulerian Stochastic Fields Solver Coupled with Reaction–Diffusion Manifolds on LES of Methane/Air Non-premixed Flames

“…Increasing the number of stochastic fields has the benefit of shifting the profiles towards the experimental values in the fuel core. However, further increasing N to 16 or 64 does not seem to improve the accuracy significantly, as observed by Hansinger et al (2020). While a single field (N = 1) might be the preferred option when using the ESF with finite rate chemistry (Breda et al 2020;Hansinger et al 2020), the use of N = 8 in this investigation does not increase significantly the computational cost, since the ESF are coupled with tabulated chemistry.…”

“…On the RHS of the equation, the scalar conditioned velocity fluctuations on the sub-grid level have been modelled using the gradient flux hypothesis. The Schmidt numbers Sc, Sc sgs have been assigned equal to 0.7 according to previous investigations (Breda et al 2020;Hansinger et al 2020). Equal diffusivities have been assumed, using unity Lewis numbers.…”

“…The number of stochastic fields N used in the ESF-REDIM solver was varied between 1, 2, 4 and 8 on mesh R. The calculation with one stochastic field is achieved by zeroing the Wiener term. A maximum of 8 fields was selected, as this number was seen to be sufficient to capture the sub-grid scalar fluctuations when applied to LES of non-premixed flames (Hansinger et al 2020;Jones and Prasad 2010;Mustata et al 2006). All meshes used in this work (SC, C and R) satisfy the Pope criterion requiring the resolution of at least 80 % of the turbulent kinetic energy (Pope 2006), as reported by Breda et al (2020).…”

“…An ESF solver was previously implemented in the in-house OpenFOAM code, based on detailed chemistry (Müller 2016). It was further validated for non-premixed (Müller 2016;Zips et al 2019) and partially premixed flames (Hansinger et al 2020). Since the target of this investigation is further reducing the computational cost required by the transport of the ESF based on a full chemistry state, the ESF transport equations were coupled with a reduced chemistry model.…”