ANSYS Advanced Solutions for Gas Turbine Combustion Gilles Eggenspieler ANSYS, Inc. 1
Agenda Steady State: New and Existing Capabilities Reduced Order Combustion Models Finite-Rate Chemistry Models Chemistry Acceleration Methods Scale Resolving Simulation (SRS) Simulation LES and Scale Adaptive Embedded and Zonal LES 2 Innovative Combustion and Pollutant Models Thickened Flame Model G-Equation Model 2011 ANSYS, Inc. CO Pollutant Modeling
An ANSYS Solution for every Simulation Challenge High Quality Fuel/Air Mixing Advanced Turbulence Models (RANS, SAS, LES) Liquid Fuel Injection DPM tracking, Advanced Break-Up Models Complex Chemistry Complete Array of Turbulent Chemistry Models Emission Predictions Post-Processing and Coupled Pollutant Models Heat Transfer Computation Advanced Wall Functions and Turbulence Models Configuration Optimization Parametric Simulation, Design Exploration Lifing Fluid-Structure Interaction, ANSYS FEA, ncode 3
A complete Portfolio of Reduced Order Combustion Models Partially-Premixed Non-Premixed Combustion Premixed Combustion Combustion Progress Variable Mixture Fraction Chemistry Tabulation - Equilibrium Chemistry - Non-Equilibrium Flamelets Compressibility Effects Non-Adiabatic Systems + Flame Speed Models - Zimont Flame Speed - Peters Flame Speed Enhanced Coherent Flame Model Compressibility Effects Non-Adiabatic Systems Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing 4 = Mixture FractionProgress Variable Approaches Chemistry Tabulation - Equilibrium Chemistry - Non-Equilibrium Flamelets Flame Speed Models - Zimont Flame Speed - Peters Flame Speed Compressibility Effects Non-Adiabatic Systems Decoupled Detailed Chemistry - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady PostProcessing
Finite-Rate Chemistry Models: An Extensive Offering Laminar Finite Rate (Chemistry Only) Eddy-Dissipation (Turbulence Only) Premixed Laminar Finite Rate/Eddy-Dissipation (Chemistry/Turbulence Interactions) Non-Premixed Eddy-Dissipation Concept (Chemistry/Turbulence Interactions) Partially Premixed Composition PDF Transport (Chemistry/Turbulence Interactions) Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing R1 Decoupled Detailed Chemistry 3 - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady PostProcessing KEY TECHNOLOGY: CHEMISTRY ACCELERATION 5
Efficient Chemistry Acceleration Solution From 2 to 10 s of Species Minor Species and Radicals Challenge Chemistry Computation Cost >> Fluid Computation Cost Stiff Reaction Rates In-Situ Adaptive Tabulation (ISAT) Chemistry Agglomeration Dimension Reduction Decoupled Detailed Chemistry 6
Efficient Chemistry Acceleration IN-SITU ADAPTIVE TABULATION CHEMISTRY AGGLOMERATION Store Reaction Mappings in an ISAT table Agglomerate cells of similar Composition Retrieve Reaction rates when needed Call ISAT on Agglomerated Cells Up to 100 Speed-Up Factor DIMENSION REDUCTION User selects the transported Species Calculate the remaining unrepresented species using constrained chemical equilibrium Allows 50+ species in the full 7 2011 ANSYS, Inc. mechanism Map Reaction Step back to Original Cells DECOUPLED DETAILED CHEMISTRY Slow chemistry (pollutants) - NO - CO Compute Chemistry (Minor Species) on a frozen (Fluid/Major Species) Field
Accurate Emission Prediction: GE LM 1600 Challenge GE LM-1600 Non-Premixed/Air-natural Gas Prediction of NO Emission Annular combustion chamber 18 nozzles ANSYS Solution Geometry Mesh High Quality Mesh Laminar Flamelet model 22 species, 104 reactions reduced GRI-MECH 1.22 mechanism Differential diffusion included Temperature Results Accurate Prediction of the Combustion Processes Accurate Prediction of the NO (Pollutant) Emissions Courtesy of Nova Research and Technology Corp. 8 NO Predictions
Innovative Particle BreakUp Model - BETA New Advanced Droplet Models for Fuel Combustion - Accurate prediction of secondary droplet break-up - Particles characteristics and locations are essential for accurate simulation on of the combustion processes STOCHASTIC SECONDARY DROPLET (SSD) Break-Up - Valid for High Weber number particles - Break-Up modeled as a discrete random event - Break-Up Distribution of Diameter over a Range ASSUMPTIONS - The probability of break-up is independent of the parent droplet size - Secondary droplet size is sampled from an analytical solution of the Fokker-Planck equation for the probability distribution - Parameters for the size distribution are based on local conditions 9...
SSD: Accurate Break-Up Prediction Challenge Simulate accurate Jet Penetration Hiroyasu tests Accurate Droplet Break Up is Required ANSYS Solution Large-Eddy Simulation SSD Break-Up Model Results Accurate Prediction of the Jet Penetration at different operating Conditions 10 Visualization of the Droplets Jet Jet Penetration Results
The Need for Scale Resolving Models Next generation Combustion Simulations requires to capture unsteady Phenomena Prediction of Combustion Dynamics Prediction of Flame instabilities which can lead to catastrophic phenomena like BlowOff or Flashback Scale Resolving Models proved to be more accurate State of the Art Scale Resolving Models in ANSYS CFD 11 Scale Adaptive Simulation Detached-Eddy Simulation Delayed Detached-Eddy Simulation Embedded Large-Eddy Simulation Large-Eddy Simulation
State of the Art Scale Resoling Models U-RANS (Unsteady RANS) URANS gives unphysical single mode unsteady behavior LES (Large Eddy Simulation) Adequate only for non wall-bounded flows Too expensive for most industrial flows due to high resolution requirements in boundary layers U-RANS DES (Detached Eddy Simulation) First industrial-strength model for high-re with LES-content Increased complexity (grid sensitivity) due to explicit mix of two modeling concepts SAS (Scale-Adaptive Simulation) Extends URANS to many technical flows Provides LES -content in unsteady regions A preferred solution for Scale Resolving Simulations of Engineering applications 12 SAS
A fully Flexible Scale-Resolving Methods Portfolio Scale Resolving Simulations are computationally expensive To capture all relevant turbulent structures, the mesh resolution is finer than typical RANS meshes To capture all relevant turbulent structures, the time step is smaller than typical U-RANS time steps ANSYS Solution: Domain Based Scale Resolving Use 13 Use Scale Resolving Methods only in Area of interest Use typical U-RANS methods in area where the resolution of unsteady turbulent structure is not needed Zonal LES for ANSYS CFX Embedded LES for ANSYS FLUENT
Efficient Scale Resolving Simulation: Sydney Flame Example Challenge Simulating the J&R Flame using an Scale Resolving Method Reduce the computational costs of the Scale Resolving Simulation LES ANSYS Solution Use the Embedded LES Method Use LES in the area of interest: combustion region Use U-RANS in regions where LES cannot be used (swirler) Use U-RANS in regions where the LES cost is not justified (inflow pipe and outflow region) Results Results as accurate as a full LES Reduced Computational cost when compared to a full LES Simulation 14 U-RANS LES U-RANS
Scale Resolving Methods for Combustion Simulations: LES Example (GE LM6000) Challenge Simulating Combustion Processes in the GE LM6000 Gas Turbine Combustion Chamber Predict the Flame location and velocity fields ANSYS Solution High Quality Mesh State of the Art Turbulence Models (LES) State of the Art Combustion Models (Premixed Model) Results Accurate Prediction of the Combustion Processes Accurate Prediction of Velocity Fields 15
Scale Resolving Methods for Combustion Dynamics: SAS Example (Siemens Dual Fuel DLE) Challenge Simulating Combustion Processes in a Gas Turbine Combustion Chamber Predict the Combustion Dynamics ANSYS Solution High Quality Mesh Advanced Turbulence Models (SAS) Results Accurate Prediction of the Combustion Processes Accurate Prediction of the Acoustics Behavior of the system Prediction of Aerodynamic Frequencies in a Gas Turbine Combustor Using Transient CFD - 2011 GT2009-59721 16 ANSYS, Inc. Double Skin Impingement Main Burner Cooled Combustor Pilot Burner PreChamber Radial Swirler
Newly Implemented Finite-Rate Unsteady Combustion Model: Thickened Flame Model In Unsteady Mode, the flame structure cannot be resolved on the computational mesh When using Finite Rate Chemistry, numerical issues (temperature spikes) can appear because of lack of Flame resolution When not resolving flame, flame speed is wrong Dynamic Thickening in the reaction zone Local Thickening Factor as a function of the mesh size ANSYS Solution: Thickened Flame Model The flame is dynamically thickened to to limit thickening to flame zone only An Efficiency Function takes into account the chemistry/turbulence Interactions 17 Flame/Turbulence Interaction: Accurate Flame Efficiency function Representation
Newly Implemented Premixed Unsteady Combustion Model: GEquation In Unsteady Mode, typical Premixed Model can predict a dissipative thick flame surface REACTANT PRODUCTS Affect accurate prediction of flame surface/turbulence interaction Degrades quality of the results G-Field: Distance from the flame (Here burnt region where G > 0) ANSYS Solution: G-Equation (Level Set) The distance from the flame front (G) is tracked the G-field is re-initialized at every iteration to ensure that in the entire domain it equals the (singed) distance to the flame front REACTANT PRODUCTS Thin Flame 18
Innovative Pollutant Model: - BETA Time-Scale Separation for CO For typical Lean and Premixed or Partially Premixed Gas Turbine Combustion Chambers: Highly non-monotonous evolution of CO Fast formation of CO at the flame front Sharp CO peak in the reaction zone Relatively slow post-flame oxidation 0.15 Y(CH4) Y(CO) Y(CO2) 0.10 Y, 0.05 CO formation at the flame front 0.00 0.000 0.005 x, m 0.010 Oxidation CO CO2 DYCO front ρ = ρyco st c + c S CO + Diffusion Dt Time-Scale Separation Solution Separates Flame Front Formation from Post-Flame Oxidation Data extracted from PDF Chemistry Tables Peak CO at the Flame Front Post-Flame CO Oxidation Rates 19 0.015
Demonstration of the CO SST Capabilities Challenge Simulating CO formation and Oxidation in a Typical Gas Turbine Combustion Chamber ANSYS Solution High Quality Mesh (2.5 M nodes) Advanced Turbulence Model (SST) Advanced CO Models (TST) Geometry Results Fast Simulation CO Predictions are in agreement with Experimental Results CFD Prediction of Partload CO Emissions using a Two-Timescale Combustion Model - GT 2010-22241 20 2011 ANSYS, Inc. Accurate Boundary Conditions Comparison with Experimental Data
The Full Power of ANSYS Workbench: Optimization, FSI, etc. ANSYS Mechanical Gas temperature 1-way coupling wall temperature ANSYS CFD Design Optimization Examples: Total deformation Equivalent elastic strain ANSYS Workbench Fluid Structure Interaction (FSI) Couples CFD and Structural Simulations Transfer Pressure Loads, Temperature Loads, CHT data, etc. 1- and 2-way FSI 21 Optimize a geometry Optimize operating conditions
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