The turbulent reacting flow in an industrial gas turbine combustor operating at 3 bar is computed using LES paradigm. The subgrid scale (SGS) combustion is modelled using a collection of unstrained premixed flamelets including mixture stratification.The non-premixed combustion mode is also included using a simple closure involving the scalar dissipation rate of the mixture fraction. A close attention is paid to maintain physical consistencies among sub-closure models for combustion and these consistencies are discussed on a physical basis. The importance of non-premixed mode and SGS mixture fraction fluctuations are investigated systematically. The results show that the SGS mixture fraction variance plays an important role and comparisons to measurements improve when contributions from the premixed and non-premixed modes are included. These numerical results and observations are discussed on a physical basis along with potential avenues for further improvements. a Research Associate, il246@cam.ac.uk b Research Associate, zc252@cam.ac.uk c Professor, ns341@cam.ac.uk d Engineer, suresh.sadasivuni@siemens.com 4 combustors. Thus, the ability of reacting flow CFD (Computational Fluid Dynamics) to capture these phenomena is crucial for their use in the design of next-generation combustors [2].Past studies have demonstrated that Large Eddy Simulation (LES) is suitable to capture aerodynamics of swirling flows, and the continuous increase of computing power allows application of LES-based models to practical burners [3][4][5][6][7]. Combustion requires modelling as it is a subgrid phenomenon in LES. Closures developed for the subgrid scale (SGS) reaction rate include: dynamic thickened flame model [8,9], linear eddy model [10], fractal flame-wrinkling model [11], partiallystirred reactor model [12], and Eulerian stochastic fields [13]. Another recently developed flamelet model for LES uses Scalar Dissipation Rate (SDR) closure [14,15], which is shown to be successful in RANS studies of industrial gas turbine combustors [16,17], but this approach has not been tested for LES of reacting flows in these combustors. This provides the motivation for this work.Due to large costs for experiments at realistic operating conditions of gas turbines (i.e. with optical access, high pressure, and preheated air), high quality validation data is rare [18]. One widely studied database is the set of laser-diagnostics obtained for Siemens SGT-100 combustor at 3 bar [19]. Analyses of these measurements and past LES results suggest that the combustion has flamelet-like properties despite the highly turbulent flow [5-7, 20, 21]. Flamelet models assume that the combustion time scale, τ c = s L /δ is shorter than the smallest turbulent scales (this also applies for length scales) implying that the flamelet structure is undisturbed by the turbulence. Thus, the SGS reaction rate can be calculated a priori using laminar flamelets. Hence, this methodology is also known as tabulated chemistry approach.Turbulent eddies can penetrate the flame-front di...

Hydrogen is receiving increasing attention as a versatile energy vector to help accelerate the transition to a decarbonised energy future. Gas turbines will continue to play a critical role in providing grid stability and resilience in future low-carbon power systems; however, it is recognised that this role is contingent upon achieving increased thermal efficiencies and the ability to operate on carbon-neutral fuels such as hydrogen. An important consideration in the development of gas turbine combustors capable of operating with pure hydrogen or hydrogen-enriched natural gas are the significant changes in thermoacoustic instability characteristics associated with burning these fuels. This article provides a review of the effects of burning hydrogen on combustion dynamics with focus on swirl-stabilised lean-premixed combustors. Experimental and numerical evidence suggests hydrogen can have either a stabilising or destabilising impact on the dynamic state of a combustor through its influence particularly on flame structure and flame position. Other operational considerations such as the effect of elevated pressure and piloting on combustion dynamics as well as recent developments in micromix burner technology for 100% hydrogen combustion have also been discussed. The insights provided in this review will aid the development of instability mitigation strategies for high hydrogen combustion.

A methodology is discussed to automatically determine the parameters of closed budget equations for chemical species mass fractions and energy, in order to simulate spatially filtered flames as required in Large Eddy Simulation (LES). The method accounts for the effects of LES filtering on chemistry and transport by simultaneously optimizing, for a reduced number of species, the Arrhenius reaction rates and a correction to mixture-averaged molecular diffusion coefficients. The objective is to match, for a given filter size, spatially filtered canonical oneDownloaded by [New York University] at 04:32 02 August 2015 A c c e p t e d M a n u s c r i p t 2 dimensional flames simulated with detailed chemistry solutions. This approach is designed for quite well-resolved LES, in which most of the unresolved fluctuations result from flame thickening due to spatial filtering, thus featuring weak levels of sub-grid scale flame wrinkling. Methane-air partially premixed combustion is addressed. A 4-step reduced reaction mechanism involving seven species is developed along with mass and heat molecular transport properties. The optimization is performed at atmospheric pressure and at 3 bar, for ranges of fresh gas temperatures [300 K-650 K] and equivalence ratios [0.4-1.2]. Comparisons with the filtered detailed chemistry solution of a planar propagating front show that the laminar flame speed, the adiabatic flame temperature, the species profiles in the reaction zone and the flow chemical composition and temperature at equilibrium are adequately predicted. The new sub-grid scale modeling approach is then applied to three-dimensional LES of an industrial gas turbine burner. Good agreement is found between the quantities predicted with LES and experimental data, in terms of flow and flame dynamics, axial velocities, averaged temperatures and some major species concentrations. Results are also improved compared to previous simulations of the same burner.

This paper presents the results of Computational Fluid Dynamics (CFD) analyses obtained for the experimental version of the SGT-100 Dry Low Emission (DLE) gas turbine burner provided by Siemens Industrial Turbomachinery Ltd (SIT). A testing and measurement campaign for this burner was previously carried out at the DLR Institute of Combustion Technology, Stuttgart, Germany, for various operating pressure conditions. The present work shows the successful validation of the CFD model in terms of time-averaged temperature and velocity data within measurement errors at an operating pressure of 3 bar. Several well known global mechanisms are tested in this work, namely the Westbrook Dryer 2-step (WD) scheme, the Jones and Lindstedt 4-step (JL4) scheme, the Meredith et al. 3-step (M3) scheme and a recently developed in-house 4-step scheme (M4) for methane-air mixtures. The M4 scheme is optimized by matching the detailed GRI-Mech 3.0 mechanism in terms of 1D laminar flame speed, using the CHEMKIN software for a wide range of pressures (1 to 6 bar), unburned gas temperatures (295 to 650 K) and equivalence ratios range (0.4 to 1.6). CFD simulations are performed using the Eddy Dissipation Model (EDM)/Finite Rate Chemistry (FRC) non-premixed turbulence chemistry interaction model. Both steady-state Reynolds Averaged Navier Stokes (RANS) and hybrid Unsteady Reynolds Averaged Navier Stokes /Large Eddy Simulation (URANS/LES) turbulence models are used. The LES Wall Adaptive Large Eddy-Viscosity (WALE) model with finite rate chemistry is also tested for validation. Velocity profiles, flame temperatures and major species are compared with experiments for different global reaction mechanisms used with different turbulence models. A reasonable agreement is found with the M4 global reaction mechanism in predicting mixing, temperatures and major species. RANS simulations are observed to underpredict the temperature profiles downstream and overpredict in the upstream region, while the velocity profiles are found to be in close agreement with experiments. The SAS-SST turbulence model predicts the velocity profiles in good agreement with experimental data and slightly better than the RANS model. Both the transient simulations slightly overpredict the temperature profiles. The LES-WALE model gives too high and unrealistic temperatures.