Large-eddy simulation of a reacting swirling flow in a model combustion chamber

We perform Large-eddy simulations of a non-premixed swirling flame in a model of a combustion chamber with a swirling air bulk flow at Re = 15000 and a central pilot low-velocity jet with methane using the Flamelet-generated manifold model. The unsteady behaviour of this regime is well reproduced based on the flame dynamics. The distribution of turbulent kinetic energy suggests the presence of intensive vortical structures typical of high-swirl flows similar to the precessing vortex core.

Numerical Steady and Transient Evaluation of a Confined Swirl Stabilized Burner

Lean premixed combustion technology became state of the art in recent heavy-duty gas turbines and aeroengines. In combustion chambers operating under fuel-lean conditions, unsteady heat release can augment pressure amplitudes, resulting in component engine damages. In order to achieve deeper knowledge concerning combustion instabilities, it is necessary to analyze in detail combustion processes. The current study supports this by conducting a numerical investigation of combustion in a premixed swirl-stabilized methane burner with operating conditions taken from experimental data that were recently published. It is a follow-up of a previous paper from Farisco et al., 2019 where a different combustion configuration was studied. The commercial code ANSYS Fluent has been used with the aim to perform steady and transient calculations via Large Eddy Simulation (LES) of the current confined methane combustor. A validation of the numerical data has been performed against the available experiments. In this study, the numerical temperature profiles have been compared with the measurements. The heat release parameter has been experimentally and numerically estimated in order to point out the position of the main reaction zone. Several turbulence and combustion models have been investigated with the aim to come into accord with the experiments. The outcome showed that the combustion model Flamelet Generated Manifold (FGM) with the k-ω turbulence model was able to correctly simulate flame lift-off.

The effects of swirl number on the combustion characteristics in an internally-staged combustor

The three-dimensional turbulent swirling flame in an internally-staged combustor is numerically investigated. Four cases over a range of swirl intensities are explored by the Flamelet Generated Manifold model in this paper. Special attention is paid to analyzing the variation of the flow field, temperature, major species concentrations and emissions. The results clearly show the effects of swirl number on the size of the center recirculation zone, fuel distribution and combustion characteristics. When the third premixed stage swirl number increases from 0.6 to 1.2, the axial length of the center recirculation zone decreases by 3.7%, while the radial length increases by 6.9%. The characteristics of the flow field play an important role in the spatial distribution of the fuel, which further affects the temperature distribution in the combustor. The backflow effect is enhanced, resulting in a greater concentration of fuel at the outlet of the swirler. After the maximum temperature is reached at the exit position of the pilot stage, the temperature decreases compared to the peak temperature downstream as the proportion of premixed combustion mode increases. This creates a high concentration region of OH at the outlet of the pilot stage injector and the heat release region is squeezed upstream. At the same time, the volume of the high-temperature region downstream of the pilot stage is reduced. In addition, as the swirl number of the third premixed stage increases from 0.6 to 1.2, the emissions of NO and CO decrease by 28.7% and 75%, respectively.

Flamelet Versus Detailed Chemistry LES for a Liquid Fueled Gas-Turbine Combustor: A Comparison of Accuracy and Computational Cost

A Honeywell liquid-fueled gas turbine test combustor, at idle conditions is numerically investigated in Simcenter STAR-CCM+. This work presents Large Eddy Simulation (LES) results using both the Flamelet Generated Manifold (FGM) and Complex Chemistry (CC) combustion models. Both take advantage of a hybrid chemical mechanism (HyChem) which has previously demonstrated very good accuracy for real fuels such as Jet-A with only 47 species. The objective of this work is to investigate the ability of FGM and CC to capture pollutant formation in an aero-engine. Comparisons for NOx, CO, Unburned Hydrocarbons, and Soot are made, along with the radial temperature pro?le. Computational costs are assessed by comparing the performance and scalability of the simulations with each of the combustion models. It is found that the CC case with clustering can reproduce nearly identical results to that without acceleration if CO is added as a clustering variable. With the Lagrangian model settings chosen for this study, the CC results compared more favorably with the experimental data than FGM, however there is uncertainty in the secondary breakup parameters. Sensitivity of the results to a key parameter in the spray breakup model are provided for both FGM and CC. By varying this breakup rate, the FGM case can predict CO, NOx, and Unburned Hydrocarbons equally well. The smoke number, however, is predicted most accurately by CC. The cost for running CC with clustering is found to be about 4 times that of FGM for this combustor and chemical mechanism.

Co Emission Modeling in a Heavy Duty Annular Combustor Operating with Natural Gas

The present paper summarizes the development of a Large-Eddy Simulation (LES) based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the Extended Turbulent Flame Speed Closure (ETFSC) of the standard Flamelet Generated Manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to de-couple the in-flame CO production region from the post-flame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

Flamelet Versus Detailed Chemistry LES for a Liquid Fueled Gas-Turbine Combustor: A Comparison of Accuracy and Computational Cost

A Honeywell liquid-fueled gas turbine test combustor, at idle conditions is numerically investigated in Simcenter STAR-CCM+ version 2020.3. This work presents Large Eddy Simulation (LES) results using both the Flamelet Generated Manifold (FGM) and detailed chemistry combustion models. Both take advantage of a hybrid chemical mechanism (HyChem) which has previously demonstrated very good accuracy for real fuels such as Jet-A with only 47 species. The objective of this work is to investigate the ability of FGM and detailed chemistry modeling to capture pollutant formation in an aero-engine combustor. Comparisons for NOx, CO, Unburned Hydrocarbons, and Soot are made, along with the radial temperature profile. To fully capture potential emissions, a soot moment model, and Zeldovich NOx model are employed along with radiation. A comparison of results with and without chemistry acceleration techniques for detailed chemistry is included. Then, computational costs are assessed by comparing the performance and scalability of the simulations with each of the combustion models. It is found that the detailed chemistry case with clustering can reproduce nearly identical results to detailed chemistry without any acceleration if CO is added as a clustering variable. With the Lagrangian model settings chosen for this study, the detailed chemistry results compared more favorably with the experimental data than FGM, however there is uncertainty in the secondary breakup parameters. Sensitivity of the results to a key parameter in the spray breakup model are provided for both FGM and Complex Chemistry (CC). By varying this breakup rate, the FGM case can predict CO, NOx, and Unburned Hydrocarbons equally well. The smoke number, however, is predicted most accurately by CC. The cost for running detailed chemistry with clustering is found to be about 4 times that of FGM for this combustor and chemical mechanism.