Assessment of Finite Rate Chemistry Large Eddy Simulation Combustion Models

E Fedina,C Fureby,G Bulat,W Meier

doi:10.1007/s10494-017-9823-0

Abstract

Large Eddy Simulations (LES) of a swirl-stabilized natural gas-air flame in a laboratory gas turbine combustor is performed using six different LES combustion models to provide a head-to-head comparative study. More specifically, six finite rate chemistry models, including the thickened flame model, the partially stirred reactor model, the approximate deconvolution model and the stochastic fields model have been studied. The LES predictions are compared against experimental data including velocity, temperature and major species concentrations measured using Particle Image Velocimetry (PIV), OH Planar Laser-Induced Fluorescence (OH-PLIF), OH chemiluminescence imaging and one-dimensional laser Raman scattering. Based on previous results a skeletal methane-air reaction mechanism based on the well-known Smooke and Giovangigli mechanism was used in this work. Two computational grids of about 7 and 56 million cells, respectively, are used to quantify the influence of grid resolution. The overall flow and flame structures appear similar for all LES combustion models studied and agree well with experimental still and video images. Takeno flame index and chemical explosives mode analysis suggest that the flame is premixed and resides within the thin reaction zone. The LES results show good agreement with the experimental data for the axial velocity, temperature and major species, but differences due to the choice of LES combustion model are observed and discussed. Furthermore, the intrinsic flame structure and the flame dynamics are similarly predicted by all LES combustion models examined. Within this range of models, there is no strong case for deciding which model performs the best.

Highlights

Introduction and BackgroundDuring the last three decades the use of Large Eddy Simulation (LES) in turbulent combustion research and engineering has increased considerably as evident from statistics of open literature journal publications
We report on an investigation of a lean premixed natural gas-air swirl flame in an industrial gas turbine combustor, [49,50,51], that has been performed aiming at comparing different finite rate chemistry LES combustion models based on the 35-step skeletal Smooke and Giovangigli reaction mechanism, [76]
The finite rate chemistry LES combustion models studied include the Thickened Flame Model (TFM), [55], the Eddy Dissipation Concept (EDC) approach, [39], the Partially Stirred Reactor (PaSR) model, [41], the Fractal Model (FM), [40], the Approximate Deconvolution Model (ADM), [42], and the Stochastic Fields (SF) model, [44, 64]. These models are all implemented in an in-house developed solver based on OpenFOAM, [67], and the equations are solved using a high-order monotonicity preserving convective recostruction algorithm, central differencing and Crank-Nicholson time-integration, [68], combined with a Strang-type, Rosenbrock, operator-splitting scheme, [69], for integrating the combustion chemistry

Summary

Introduction and Background

During the last three decades the use of Large Eddy Simulation (LES) in turbulent combustion research and engineering has increased considerably as evident from statistics of open literature journal publications. Combustion LES is based on the reactive Navier-Stokes Equations (NSE) and employs low-pass filtering, [12], to eliminate the small-scale flow physics not resolved on the computational grid. Besides the subgrid flow modeling and the modeling of the combustion chemistry, the ability to resolve and/or model the turbulent reaction front is the other major challenge in combustion LES This is manifested by the filtered reaction rates in the species transport equations, which are directly related to the underlying (detailed, skeletal or global) reaction mechanisms. The particular configuration selected has previously been experimentally examined in a series of papers, [49,50,51], resulting in a rather comprehensive experimental database including velocity, temperature and major species data This set-up has previously been successfully simulated with LES using different codes and different finite rate chemistry LES combustion models, e.g. The temperature was deduced from the total number density via the ideal

LES Models and Numerical Methods

Chemical Kinetics

Results and Discussion

Concluding Remarks