LES Prediction of Combustor Emissions From a Practical Industrial Fuel Injector

2003 ◽  
Author(s):  
Steven M. Cannon ◽  
Baifang Zuo ◽  
Clifford E. Smith
Keyword(s):  
Equivalence Ratio ◽  
Chemical Species ◽  
Experimental Tests ◽  
Fuel Injector ◽  
Time Resolved ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Large Eddy ◽  
General Transport ◽  
Flow Boundaries

An axial-swirl, lean premixed fuel injector typical of stationary gas turbine combustors has been analyzed using Large Eddy Simulation (LES). The objective of the study was to evaluate the LES modeling approach for predicting emissions of CO and NOx at practical engine conditions (P = 13.6 atm, Tin = 734 K = 861°F) and over a range of natural gas-air equivalence ratios (0.42 to 0.58). Experimental data from a recent UTRC/DOE-NETL program was used to evaluate the model. The experimental tests found NOx emissions decreased significantly with a decrease in equivalence ratio while CO emissions decreased initially, but then increased at the leanest conditions. LES calculations were performed using a parallel (domain decomposition), pressure-based, unstructured-grid flow solver within the CFD-ACE+ commercial software. The LES software solves the general transport equations for mass, momentum, energy, and chemical species without assumption at the grid- and time-resolved scales of the flow, and models the turbulent mixing and chemistry below the locally resolved grid/time-scales. The Localized Dynamic subgrid Kinetic energy Model (LDKM) was used to model the unresolved turbulence and a 2-step assumed PDF method, with decoupled NOx, was used to model the unresolved turbulence-chemistry interactions. Parallel calculations on a cluster of 22 Linux-based PCs were carried out. It was shown that LES was able to accurately predict the CO and NOx at an equivalence ratio of 0.58, and at leaner equivalence ratios the model was able to give qualitative agreement with the measurements. Some inadequacies in the NOx chemistry at ultra lean conditions and the near-wall flow boundaries were observed.

scholarly journals Large-Eddy Simulation of Wind Turbine Flows: A New Evaluation of Actuator Disk Models

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3745
Author(s):  
Tristan Revaz ◽  
Fernando Porté-Agel
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Wind Turbine ◽  
Wake Flow ◽  
Test Case ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Flow ◽  
Advanced Model

Large-eddy simulation (LES) with actuator models has become the state-of-the-art numerical tool to study the complex interaction between the atmospheric boundary layer (ABL) and wind turbines. In this paper, a new evaluation of actuator disk models (ADMs) for LES of wind turbine flows is presented. Several details of the implementation of such models are evaluated based on a test case studied experimentally. In contrast to other test cases used in previous similar studies, the present test case consists of a wind turbine immersed in a realistic turbulent boundary-layer flow, for which accurate data for the turbine, the flow, the thrust and the power are available. It is found that the projection of the forces generated by the turbine into the flow solver grid is crucial for rotor predictions, especially for the power, and less important for the wake flow prediction. In this context, the projection of the forces into the flow solver grid should be as accurate as possible, in order to conserve the consistency between the computed axial velocity and the projected axial force. Also, the projection of the force is found to be much more important in the rotor plane directions than in the streamwise direction. It is found that for the case of a wind turbine immersed in a realistic turbulent boundary-layer flow, the potential spurious numerical oscillations originating from sharp force projections are not harmful to the results. By comparing an advanced model which computes the non-uniform distribution of the turbine forces over the rotor with a simple model which assumes uniform effects of the turbine forces, it is found that both can lead to accurate results for the far wake flow and the thrust and power predictions. However, the comparison shows that the advanced model leads to better results for the near wake flow. In addition, it is found that the simple model overestimates the rotor velocity prediction in comparison to the advanced model. These elements are explained by the lack of local feedback between the axial velocity and the axial force in the simple model. By comparing simulations with and without including the effects of the nacelle and tower, it is found that the consideration of the nacelle and tower is relatively important both for the near wake and the power prediction, due to the shadow effects. The grid resolution is not found to be critical once a reasonable resolution is used, i.e. in the order of 10 grid points along each direction across the rotor. The comparison with the experimental data shows that an accurate prediction of the flow, thrust, and power is possible with a very reasonable computational cost. Overall, the results give important guidelines for the implementation of ADMs for LES.

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

scholarly journals Non-steady wind turbine response to daytime atmospheric turbulence

2017 ◽  
Vol 375 (2091) ◽  
pp. 20160103 ◽  
Author(s):  
Tarak N. Nandi ◽  
Andreas Herrig ◽  
James G. Brasseur
Keyword(s):  
Field Experiment ◽  
Wind Turbine ◽  
Atmospheric Turbulence ◽  
Time Scales ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Atmospheric Conditions ◽  
Time Resolved ◽  
Eddy Simulation ◽  
Large Eddy

Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25–50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions. This article is part of the themed issue ‘Wind energy in complex terrains’.

scholarly journals Mixing in Turbulent Flows: An Overview of Physics and Modelling

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1379
Author(s):  
Jacek Pozorski ◽  
Marta Wacławczyk
Keyword(s):  
Density Function ◽  
Turbulent Flows ◽  
Chemical Species ◽  
Scalar Fields ◽  
Industrial Applications ◽  
Mixing Models ◽  
Computing Technology ◽  
Filtered Density Function ◽  
Eddy Simulation ◽  
Large Eddy

Turbulent flows featuring additional scalar fields, such as chemical species or temperature, are common in environmental and industrial applications. Their physics is complex because of a broad range of scales involved; hence, efficient computational approaches remain a challenge. In this paper, we present an overview of such flows (with no particular emphasis on combustion, however) and we recall the major types of micro-mixing models developed within the statistical approaches to turbulence (the probability density function approach) as well as in the large-eddy simulation context (the filtered density function). We also report on some trends in algorithm development with respect to the recent progress in computing technology.

The Effects of Forcing Direction on the Flame Transfer Function of a Lean-Burn Spray Flame

2021 ◽  
Author(s):  
Nicholas C. W. Treleaven ◽  
André Fischer ◽  
Claus Lahiri ◽  
Max Staufer ◽  
Andrew Garmory ◽  
...  
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Fuel Injector ◽  
Lean Burn ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Reproduction ◽  
Small Change

Abstract The flame transfer function (FTF) of an industrial lean-burn fuel injector has been computed using large eddy simulation (LES) and compared to experimental measurements using the multi-microphone technique and OH* measurements. The flame transfer function relates the fluctuations of heat release in the combustion chamber to fluctuations of airflow through the fuel injector and is a critical part of thermoacoustic analysis of combustion systems. The multi-microphone method derives the FTF by forcing the flame acoustically, alternating from the upstream and downstream side. Simulations emulating this methodology have been completed using compressible large eddy simulations (LES). These simulations are also used to derive an FTF by measuring the fluctuations of mass flow rate and heat release rate directly which reduces the number of simulations per frequency to one, significantly reducing the simulation cost. Simulations acoustically forced from downstream are shown to result in a lower value of the FTF gain than simulations forced from upstream with a small change in phase, this is shown to be consistent with theory. Through using a slightly different definition of the FTF, this is also shown to be consistent with measurements of the heat release rate using OH* chemiluminescence however these results are inconsistent with the multi-microphone method result. The discrepancy comes from not having an accurate measurement of the acoustic impedance at the exit plane of the injector and from certain convective phenomena that alter the downstream velocity and pressure field with respect to the purely acoustic signal. All simulations show a lower gain in the FTF than the experiments but with good reproduction of phase. Previous work suggests this error is likely due to fluctuations of the fuel spray atomisation process due to the acoustic forcing which is not modelled in this study.

Application of Large Eddy Simulation for HA_Class Combustion System Design to Mitigate Combustion Instabilities (Frequency, and Amplitude)

2021 ◽  
Author(s):  
Azardokht Hajiloo ◽  
Venkat Narra ◽  
Erin Krumenacker ◽  
Hasan Karim ◽  
Lee Shunn ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Combustion Dynamics ◽  
Flow Solver ◽  
Turbine Engine ◽  
Eddy Simulation ◽  
Design Changes ◽  
Large Eddy ◽  
Fuel Staging ◽  
Increasing Demand ◽  
Engine Testing

Abstract Enabled by national commercialization of massive shale resources, Gas Turbines continue to be the backbone of power generation in the US. With the ever-increasing demand on efficiency, GT combustion sections have evolved to include shorter combustion lengths and multiple axial staging of the fuel, while at the same time operating at ever increasing temperatures. This paper presents the results of very detailed Large Eddy Simulations of one (or two) combustor can(s) for a 7HA GE Gas Turbine Engine over a range of operating parameters. The model of the simulated combustor can(s) includes (include) all the details of the combustor from compressor diffuser to the end of the stationary part of the first stage of the turbine. It includes the geometries of multiple pre-mixers within the combustion can(s) and the complete design features for axial fuel staging. All simulations in this work are performed using the CharLES flow solver developed by Cascade Technologies. CharLES is a suite of massively parallel CFD tools designed specifically for multiphysics LES in high-fidelity engineering applications. Thermo acoustic results from LES were validated first in the physical GE lab and then in full-engine testing. Both the trend as well as the predicted amplitudes for the excited axial dominant combustion mode matched the data produced in the lab and in the engine. The simulations also revealed insight into the ingestion of hot gases by different hardware pieces that may occur when machine operates under medium to high combustion dynamics amplitudes. This insight then informed the subsequent design changes which were made to the existing hardware to mitigate the problems encountered.

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