Unsteady RANS and scale adaptive simulations of a turbulent spray flame in a swirled-stabilized gas turbine model combustor using tabulated chemistry

2015 ◽  
Vol 25 (5) ◽  
pp. 1064-1088 ◽  
Author(s):  
Alain Fossi ◽  
Alain DeChamplain ◽  
Benjamin Akih-Kumgeh
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Turbulence Models ◽  
Combustion Model ◽  
Time Step ◽  
Content Type ◽  
Spray Flame ◽  
Tabulated Chemistry

Purpose – The purpose of this paper is to numerically investigate the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor using the commercial computational fluid dynamic (CFD) software ANSYS FLUENT. The first scope of the study aims to explicitly compare the predictive capabilities of two turbulence models namely Unsteady Reynolds Averaged Navier-Stokes and Scale Adaptive Simulation for a reasonable trade-off between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium(NEQ) effects caused by turbulent strain such as flame stretching. Design/methodology/approach – Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases, respectively. The computing method includes a two-way coupling in which phase properties and spray source terms are interchanging between the two phases within each coupling time step. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane+toluene) are used as jet-A1 surrogates. The combustion model is based on the mean mixture fraction and its variance, and a presumed-probability density function is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the equilibrium (EQ) assumption and thereafter, detailed NEQ calculations through the steady flamelets concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1,045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0 using a sensitivity based method, Alternate Species Elimination. Findings – Numerical results of the gas velocity, the gas temperature and the species molar fractions are compared with their experimental counterparts obtained from a steady state flame available in the literature. It is observed that, SAS coupled to the tabulated flamelet-based chemistry, predicts reasonably the main flame trends, while URANS even provided with the same combustion model and computing resources, leads to a poor prediction of the global flame trends, emphasizing the asset of a proper resolution when simulating spray flames. Research limitations/implications – The steady flamelet model even coupled with a robust turbulence model does not reproduce accurately the trend of species with slow oxidation kinetics such as CO and H2, because of the restrictiveness of the solutions space of flamelet equations and the assumption of unity Lewis for all species. Practical implications – This work is adding a contribution for spray flame modeling and can be seen as an extension to the significant efforts for the modeling of gaseous flames using robust turbulence models coupled with the tabulated flamelet-based chemistry approach to considerably reduce computing cost. The exclusive use of a commercial CFD code widely used in the industry allows a direct application of this simulation approach to industrial configurations while keeping computing cost reasonable. Originality/value – This study is useful to engineers interested in designing combustors of gas turbines and others combustion systems fed with liquid fuels.

Scale-Adaptive and Large Eddy Simulations of a Turbulent Spray Flame in a Scaled Swirl-Stabilized Gas Turbine Combustor Using Strained Flamelets

2015 ◽  
Author(s):  
Alain Fossi ◽  
Alain deChamplain ◽  
Bernard Paquet ◽  
Smail Kalla ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Gas Turbine ◽  
Computing Time ◽  
Turbulence Models ◽  
Superior Performance ◽  
Combustion Model ◽  
Published Data ◽  
Gas Turbine Combustor ◽  
Spray Flame ◽  
Large Eddy ◽  
Non Equilibrium

In this paper, the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor is numerically investigated using the commercial CFD software ANSYS FLUENT™-v14. The first scope of this study aims to explicitly compare the predictive capabilities of two turbulence models namely Scale-Adaptive Simulation (SAS) and Large Eddy Simulation (LES) for a reasonable compromise between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium effects caused by turbulent strain. Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases respectively. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane + toluene) are used as jet-A1 surrogates. The combustion model is based on the first and second moments of the mixture fraction, and a presumed-probability density function (PDF) is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the partial equilibrium assumption (PEQ) and thereafter, the detailed non-equilibrium (NEQ) calculations through the laminar flamelet concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1 045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0. Numerical results are compared with a set of published data for a steady spray flame. Firstly, it is observed that, by coupling the two turbulence models with a combustion model incorporating a representative chemistry to account for non-equilibrium effects with realistic fuel properties, the models predict reasonably well the main combustion trends, with a superior performance for LES in terms of trade-off between accuracy and computing time. Secondly, because of some assumptions with the combustion model, some discrepancies are found in the prediction of species slowly produced or consumed such as CO and H2. Finally, the study emphasizes the dominant advantage of an adequate resolution of the mixing characteristics especially with the more demanding simulation of a swirl-stabilized spray flame.

Investigation of Siemens SGT-800 Industrial Gas Turbine Combustor Using Different Combustion and Turbulence Models

2016 ◽  
Author(s):  
Daniel Lörstad ◽  
Anders Ljung ◽  
Abdallah Abou-Taouk
Keyword(s):  
Gas Turbine ◽  
Burning Velocity ◽  
Computational Cost ◽  
Turbulence Models ◽  
Combined Cycle ◽  
Combustion Model ◽  
Gas Turbine Combustor ◽  
Annular Combustor ◽  
Industrial Gas Turbine ◽  
Spurious Results

Siemens SGT-800 gas turbine is the largest industrial gas turbine within Siemens medium gas turbine size range. The power rating is 53MW at 39% electrical efficiency in open cycle (ISO) and, for its power range, world class combined-cycle performance of >56%. The SGT-800 convectively cooled annular combustor with 30 Dry Low Emissions (DLE) burners has proven, for 50–100% load range, NOx emissions below 15/25ppm for gas/liquids fuels and CO emissions below 5ppm for all fuels, as well as extensive gas fuel flexible DLE capability. In this work the focus is on the combustion modelling of one burner sector of the SGT-800 annular combustor, which includes several challenges since various different physical phenomena interacts in the process. One of the most important aspects of the combustion in a gas turbine combustor is the turbulence chemistry interaction, which is dependent on both the turbulence model and the combustion model. Some turbulence-combustion model combinations that have shown reasonable results for academic generic cases and/or industrial applications at low pressure, might fail when applied to complex geometries at industrial gas turbine conditions since the combustion regime may be different. Therefore is here evaluated the performance of Reynolds Averaged Navier-Stokes (RANS) and Scale Adaptive Simulation (SAS) turbulence models combined with different combustion models, which includes the Eddy Dissipation Model (EDM) combined with Finite Rate Chemistry (FRC) using an optimized reduced 4-step scheme and two flamelet based models; Zimont’s Burning Velocity model and Lindstedt & Vaos Fractal model. The results are compared to obtained engine data and field experience, which includes for example flame position in order to evaluate the advantages and drawbacks of each model. All models could predict the flame shape and position in reasonable agreement with available data; however, for the flamelet based methods adjusted calibration constants were required to avoid a flame too far upstream or non-sufficient burn out which is not in agreement with engine data. In addition both the flamelet based models suffer from spurious results when fresh air is mixed into fully reacted gases and BVM also from spurious results inside the fuel system. The combined EDM-FRC with a properly optimized reduced chemical kinetic scheme seems to minimize these issues without the need of any calibration, with only a slight increase in computational cost.

scholarly journals Computational Modeling of Boundary Layer Flashback in a Swirling Stratified Flame Using a LES-Based Non-Adiabatic Tabulated Chemistry Approach

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 567
Author(s):  
Xudong Jiang ◽  
Yihao Tang ◽  
Zhaohui Liu ◽  
Venkat Raman
Keyword(s):  
Boundary Layer ◽  
Heat Loss ◽  
Boundary Layers ◽  
Gas Turbines ◽  
Predictive Accuracy ◽  
Safety Issue ◽  
Combustion Model ◽  
Tabulated Chemistry ◽  
Lean Fuel ◽  
Flame Flashback

When operating under lean fuel–air conditions, flame flashback is an operational safety issue in stationary gas turbines. In particular, with the increased use of hydrogen, the propagation of the flame through the boundary layers into the mixing section becomes feasible. Typically, these mixing regions are not designed to hold a high-temperature flame and can lead to catastrophic failure of the gas turbine. Flame flashback along the boundary layers is a competition between chemical reactions in a turbulent flow, where fuel and air are incompletely mixed, and heat loss to the wall that promotes flame quenching. The focus of this work is to develop a comprehensive simulation approach to model boundary layer flashback, accounting for fuel–air stratification and wall heat loss. A large eddy simulation (LES) based framework is used, along with a tabulation-based combustion model. Different approaches to tabulation and the effect of wall heat loss are studied. An experimental flashback configuration is used to understand the predictive accuracy of the models. It is shown that diffusion-flame-based tabulation methods are better suited due to the flashback occurring in relatively low-strain and lean fuel–air mixtures. Further, the flashback is promoted by the formation of features such as flame tongues, which induce negative velocity separated boundary layer flow that promotes upstream flame motion. The wall heat loss alters the strength of these separated flows, which in turn affects the flashback propensity. Comparisons with experimental data for both non-reacting cases that quantify fuel–air mixing and reacting flashback cases are used to demonstrate predictive accuracy.

A Modular Code for Real Time Dynamic Simulation of Gas Turbines in Simulink

2002 ◽  
Vol 128 (3) ◽  
pp. 506-517 ◽  
Author(s):  
S. M. Camporeale ◽  
B. Fortunato ◽  
M. Mastrovito
Keyword(s):  
Mathematical Model ◽  
Real Time ◽  
Gas Turbine ◽  
Dynamic Behavior ◽  
Gas Turbines ◽  
Simulation Software ◽  
Computational Time ◽  
High Fidelity ◽  
Time Step ◽  
The Mathematical Model

A high-fidelity real-time simulation code based on a lumped, nonlinear representation of gas turbine components is presented. The code is a general-purpose simulation software environment useful for setting up and testing control equipments. The mathematical model and the numerical procedure are specially developed in order to efficiently solve the set of algebraic and ordinary differential equations that describe the dynamic behavior of gas turbine engines. For high-fidelity purposes, the mathematical model takes into account the actual composition of the working gases and the variation of the specific heats with the temperature, including a stage-by-stage model of the air-cooled expansion. The paper presents the model and the adopted solver procedure. The code, developed in Matlab-Simulink using an object-oriented approach, is flexible and can be easily adapted to any kind of plant configuration. Simulation tests of the transients after load rejection have been carried out for a single-shaft heavy-duty gas turbine and a double-shaft aero-derivative industrial engine. Time plots of the main variables that describe the gas turbine dynamic behavior are shown and the results regarding the computational time per time step are discussed.

scholarly journals Scale-Resolving Simulation of a Propane-Fuelled Industrial Gas Turbine Combustor Using Finite-Rate Tabulated Chemistry

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 126 ◽  
Author(s):  
Kai Zhang ◽  
Ali Ghobadian ◽  
Jamshid M. Nouri
Keyword(s):  
Gas Turbine ◽  
Chemical Reaction ◽  
Turbulent Flame ◽  
Lower Amount ◽  
Combustion Model ◽  
Gas Turbine Combustor ◽  
Finite Rate ◽  
Chemistry Method ◽  
Tabulated Chemistry ◽  
Partially Premixed

The scale-resolving simulation of a practical gas turbine combustor is performed using a partially premixed finite-rate chemistry combustion model. The combustion model assumes finite-rate chemistry by limiting the chemical reaction rate with flame speed. A comparison of the numerical results with the experimental temperature and species mole fraction clearly showed the superiority of the shear stress transport, K-omega, scale adaptive turbulence model (SSTKWSAS). The model outperforms large eddy simulation (LES) in the primary region of the combustor, probably for two reasons. First, the lower amount of mesh employed in the simulation for the industrial-size combustor does not fit the LES’s explicit mesh size dependency requirement, while it is sufficient for the SSTKWSAS simulation. Second, coupling the finite-rate chemistry method with the SSTKWSAS model provides a more reasonable rate of chemical reaction than that predicted by the fast chemistry method used in LES simulation. Other than comparing with the LES data available in the literature, the SSTKWSAS-predicted result is also compared comprehensively with that obtained from the model based on the unsteady Reynolds-averaged Navier–Stokes (URANS) simulation approach. The superiority of the SSTKWSAS model in resolving large eddies is highlighted. Overall, the present study emphasizes the effectiveness and efficiency of coupling a partially premixed combustion model with a scale-resolving simulation method in predicting a swirl-stabilized, multi-jets turbulent flame in a practical, complex gas turbine combustor configuration.

A Method to Evaluate the Sensitivity of Aerodynamic Damping to Mode Shape Perturbations

2019 ◽  
Author(s):  
Jing Li ◽  
Suryarghya Chakrabarti ◽  
Wei-Min Ren
Keyword(s):  
Mode Shape ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Assessment Process ◽  
Mode Shapes ◽  
Shape Sensitivity ◽  
Aerodynamic Damping ◽  
Damped System ◽  
Cfd Analyses

Abstract Turbomachinery blade mode shapes are routinely predicted by finite element method (FEM) programs and are then used in unsteady computational fluid dynamic (CFD) analyses to predict the aerodynamic damping. This flutter stability assessment process is critical for the last-stage blades (LSBs) of modern heavy-duty gas turbines (HDGTs) which can be particularly susceptible to flutter. Evidences suggest that actual mode shapes may deviate from the FEM predictions due to changes in the FEM boundary or loading conditions, effects of the nonlinear friction contacts, and blade-to-blade variations (mistuning), among others. This uncertainty in the mode shape is accompanied by a general lack of knowledge on the sensitivity of the aerodynamic damping to a small change in mode shape. This paper presents a method to perturb a mode shape and estimate the corresponding change in aerodynamic damping in a framework enabled by linear theories and a rigid-body, quasi-3D treatment of mode shapes. This method is of low computational cost and is suitable for use in the preliminary design cycle. The numerical validation and applications of the method are demonstrated on two LSB blades. Results suggest that the mode shape sensitivity can be substantial and may even exceed the change in aerodynamic damping of a frictionally damped system when subjected to various levels of excitation.

NOx Emissions Reduction in an Innovative Industrial Gas Turbine Combustor (GE10 Machine): A Numerical Study of the Benefits of a New Pilot-System on Flame Structure and Emissions

2005 ◽  
Author(s):  
Antonio Andreini ◽  
Bruno Facchini ◽  
Luca Mangani ◽  
Antonio Asti ◽  
Gianni Ceccherini ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Numerical Study ◽  
Flame Structure ◽  
Combustion Model ◽  
Emissions Reduction ◽  
Minimal Amount ◽  
Nox Emissions ◽  
Ambient Temperatures ◽  
Wide Range

One of the driving requirements in gas turbine design is emissions reduction. In the mature markets (especially the North America), permits to install new gas turbines are granted provided emissions meet more and more restrictive requirements, in a wide range of ambient temperatures and loads. To meet such requirements, design techniques have to take advantage also of the most recent CFD tools. As a successful example of this, this paper reports the results of a reactive 3D numerical study of a single-can combustor for the GE10 machine, recently updated by GE-Energy. This work aims to evaluate the benefits on the flame shape and on NOx emissions of a new pilot-system located on the upper part of the liner. The former GE10 combustor is equipped with fuel-injecting-holes realizing purely diffusive pilot-flames. To reduce NOx emissions from the current 25 ppmvd@15%O2 to less than 15 ppmvd@15%O2 (in the ambient temperature range from −28.9°C to +37.8°C and in the load range from 50% and 100%), the new version of the combustor is equipped with 4 swirler-burners realizing lean-premixed pilot flames; these flames in turn are stabilized by a minimal amount of lean-diffusive sub-pilot-fuel. The overall goal of this new configuration is the reduction of the fraction of fuel burnt in diffusive flames, lowering peak temperatures and therefore NOx emissions. To analyse the new flame structure and to check the emissions reduction, a reactive RANS study was performed using STAR-CD™ package. A user-defined combustion model was used, while to estimate NOx emissions a specific scheme was also developed. Three different ambient temperatures (ISO, −28.9°C and 37.8°C) were simulated. Results were then compared with experimental measurements (taken both from the engine and from the rig), resulting in reasonable agreement. Finally, an additional simulation with an advanced combustion model, based on the laminar flamelet approach, was performed. The model is based on the G-Equation scheme but was modified to study partially premixed flames. A geometric procedure to solve G-Equation was implemented as add-on in STAR-CD™.

Numerical Benchmark of Turbulence Modeling in Gas Turbine Rotor-Stator System

2010 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Luca Innocenti ◽  
Antonio Andreini ◽  
Se´bastien Poncet
Keyword(s):  
Gas Turbine ◽  
Boundary Layers ◽  
Correction Term ◽  
Computational Cost ◽  
Turbulence Models ◽  
Turbine Rotor ◽  
Operating Conditions ◽  
Curvature Effects ◽  
Low Reynolds ◽  
Secondary Air

Accurate design of the secondary air system is one of the main tasks for reliability and performance of gas turbine engines. The selection of a suitable turbulence model for the study of rotor-stator cavity flows, which remains an open issue in the literature, is here addressed for several operating conditions. A numerical benchmark of turbulence models is indeed proposed in the case of rotor-stator disk flows with and without superimposed throughflow. The predictions obtained by the means of several two equation turbulence models available within the CFD solver Ansys CFX 12.0 are compared with those previously evaluated by Poncet et al. (1; 2) through the Reynolds Stress Model (RSM) of Elena and Schiestel (3; 4) implemented in a proprietary finite volume code. The standard k-ε and k-ω SST models including high and low Reynolds approaches, have been used for all calculations presented here. Furthermore, some tests were performed using the innovative k-ω SST-CC and k-ω SST-RM models that take into account the curvature effects via the Spalart-Shur correction term (5) and the reattachement modification proposed by Menter (6) respectively. The numerical calculations have been compared to extensive velocity and pressure measurements performed on the test rig of the IRPHE’s laboratory in Marseilles (1; 2). Several configurations, covering a large range of real engine operating conditions, were considered. The influence of the typical non dimensional flow parameters (Reynolds number and flowrate coefficient) on the flow structure is studied in detail. In the case of an enclosed cavity, the flow exhibits a Batchelor-like structure with two turbulent boundary layers separated by a laminar rotating core. When an inward axial throughflow is superimposed, the flow remains of Batchelor type with a core rotating faster than the disk because of conservation of the angular momentum. In this case, turbulence intensities are mainly confined close to the stator. Turbulence models based on a low Reynolds approach provide better overall results for the mean and turbulent fields especially within the very thin boundary layers. The standard k-ω SST model offers the best trade-off between accuracy and computational cost for the parameters considered here. In the case of an outward throughflow, the k-ω SST in conjunction with a low Reynolds approach and RSM models provide similar results and predict quite well the transition from the Batchelor to the Stewartson structures.

Strongly Coupled Fluid-Structure Interactions via a New Navier-Stokes Method for Prediction of Vortex-Induced Vibrations

2005 ◽  
Author(s):  
Yannis Kallinderis ◽  
Hyung Taek Ahn
Keyword(s):  
Stokes Equations ◽  
Computational Cost ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Design Tool ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equations ◽  
Vortex Induced Vibrations ◽  
Offshore Industry

Numerical prediction of vortex-induced vibrations requires employment of the unsteady Navier-Stokes equations. Current Navier-Stokes solvers are quite expensive for three-dimensional flow-structure applications. Acceptance of Computational Fluid Dynamics as a design tool for the offshore industry requires improvements to current CFD methods in order to address the following important issues: (i) stability and computation cost of the numerical simulation process, (ii) restriction on the size of the allowable time-step due to the coupling of the flow and structure solution processes, (iii) excessive number of computational elements for 3-D applications, and (iv) accuracy and computational cost of turbulence models used for high Reynolds number flow. The above four problems are addressed via a new numerical method which employs strong coupling between the flow and the structure solutions. Special coupling is also employed between the Reynolds-averaged Navier-Stokes equations and the Spalart-Allmaras turbulence model. An element-type independent spatial discretization scheme is also presented which can handle general hybrid meshes consisting of hexahedra, prisms, pyramids, and tetrahedral.

scholarly journals Comparison of Tabulated and Complex Chemistry Turbulent-Chemistry Interaction Models With High Fidelity Large Eddy Simulations on Hydrogen Flames

2020 ◽  
Author(s):  
M. Zghal ◽  
X. Sun ◽  
P. Q. Gauthier ◽  
V. Sethi
Keyword(s):  
Gas Turbines ◽  
Diffusion Flames ◽  
Computational Cost ◽  
Numerical Approach ◽  
Civil Aviation ◽  
Combustion Model ◽  
Flammability Limits ◽  
Small Diffusion ◽  
Flamelet Generated Manifold ◽  
Complex Chemistry

Abstract Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The EU H2020 ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a crossflow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios. In order to mature the hydrogen micromix combustion technology, high quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential. In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon. The Flamelet Generated Manifold (FGM) model is a combustion model that has been used in the past decades for its predicting capabilities and its low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms. However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as Hydrogen. Therefore, it is necessary to compare the FGM model to another combustion modelling approach which uses more detailed complex chemistry. The main focus of this paper then, is to compare the flame characteristics in terms of position, thickness, length, temperature and emissions obtained from LES simulations done with the FGM model, to the results obtained with more complex chemistry models, for hydrogen micromix flames. This will be done using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx.

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