ANSYS Combustion Analysis Solutions - Overview and Update Gilles Eggenspieler ANSYS, Inc. 1
Agenda Overview of Combustion Analysis Solution Reduced Order Models Finite Rate Models Pollutant Models Examples and Validations Advanced Combustion Analysis Solutions Scale Resolving Models New Combustion Models Examples and Validation 2
Combustion Modeling Dispersed Phase Models (Solid/liquid fuels) Droplet/particle dynamics Evaporation Devolatilization Heterogeneous reaction Governing Transport Equations Turbulence models LES RANS k-epsilon k-omega RSM.. Infinitely fast chemistry Da >> 1 Reaction Models - Eddy Dissipation model - Premixed model - Non-premixed model - Partially premixed model Mass Momentum + Turbulence Energy Chemical Species Finite rate chemistry Da ~ 1 Reaction Models - Laminar Flamelet model - Laminar Finite rate model - EDC - Composition PDF 3 Pollutant Models NOx SOx Soot Radiative Heat Transfer Models
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 4
A complete Portfolio of Reduced Order Combustion Models Non-Premixed Combustion Mixture Fraction Chemistry Tabulation - Equilibrium Chemistry - Non-Equilibrium Flamelets Compressibility Effects Non-Adiabatic Systems + Premixed Combustion Progress Variable Flame Speed Models - Zimont Flame Speed - Peters Flame Speed Enhanced Coherent Flame Model Compressibility Effects Non-Adiabatic Systems R13 = Partially-Premixed Combustion Mixture Fraction-Progress Variable Approaches Chemistry Tabulation - Equilibrium Chemistry - Non-Equilibrium Flamelets Flame Speed Models - Zimont Flame Speed - Peters Flame Speed Compressibility Effects Non-Adiabatic Systems Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing R13 Decoupled Detailed Chemistry - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady Post-Processing 5
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 High Quality Mesh Laminar Flamelet model 22 species, 104 reactions reduced GRI- MECH 1.22 mechanism Differential diffusion included Results Accurate Prediction of the Combustion Processes Accurate Prediction of the NO (Pollutant) Emissions Courtesy of Nova Research and Technology Corp. NO Predictions Mesh Geometry Temperature 6
Furnaces Retrofit Challenge Pollutant Control Stable Flame under different Load Minimize Wall Erosion Determine Optimum Air Staging ANSYS Solution High Quality Mesh Laminar Flamelet model SNCR Local NO x Reduction Results Downtime due to trials-and-errors was avoided Effect of multiple Staging Approaches was studied Optimal Air Staging was determined Before air staging Courtesy of Babcock Power, Inc After air staging 7
Finite-Rate Chemistry Models: An Extensive Offering Laminar Finite Rate (Chemistry Only) Eddy-Dissipation (Turbulence Only) Laminar Finite Rate/Eddy-Dissipation (Chemistry/Turbulence Interactions) Eddy-Dissipation Concept (Chemistry/Turbulence Interactions) Premixed Non-Premixed Partially Premixed Composition PDF Transport (Chemistry/Turbulence Interactions) Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing R13 Decoupled Detailed Chemistry - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady Post-Processing KEY TECHNOLOGY: CHEMISTRY ACCELERATION 8
Efficient Chemistry Acceleration From 2 to 10 s of Species Minor Species and Radicals Stiff Reaction Rates Challenge Chemistry Computation Cost >> Fluid Computation Cost Solution In-Situ Adaptive Tabulation (ISAT) Chemistry Agglomeration R13 Dimension Reduction R13 Decoupled Detailed Chemistry R13 9
Efficient Chemistry Acceleration IN-SITU ADAPTIVE TABULATION CHEMISTRY AGGLOMERATION R13 Store Reaction Mappings in an ISAT table Retrieve Reaction rates when needed Up to 100 Speed-Up Factor Agglomerate cells of similar Composition Call ISAT on Agglomerated Cells Map Reaction Step back to Original Cells DIMENSION REDUCTION R13 DECOUPLED DETAILED CHEMISTRY R13 User selects the transported Species Calculate the remaining unrepresented species using constrained chemical equilibrium Allows 50+ species in the full mechanism Slow chemistry (pollutants) - NO - CO Compute Chemistry (Minor Species) on a frozen (Fluid/Major Species) Field 10
Retrofitting a 820 MW Power Station Challenge Retrofit a Power Combustion System to Oxy-Fuel Combustion Maintain Temperature Distribution ANSYS Solution High Quality Mesh Realizable k- Turbulence Model Finite Rate EDC Model Results Oxygen/Fuel Mixture is adjusted to reach the same Temperature Distribution Avoids the need for a Complex and Expensive Test Rig Temperature O2 volume fraction Development of Oxy-fuel Combustion Technology for Existing Power Plants, Song Wu, et al. Courtesy: Wu et al, Hitachi Power Systems America, Ltd 11
Challenge Studying BioMass Combustion Study a BioMass Combustion Chamber ANSYS Solution High Quality Mesh Realizable k- Turbulence Model Discrete Phase Injection Results Flame Length increase with the amount of BioMass Content Delayed Combustion for large Particles Validation using Freeman et al. data * (*) Results of Pilot-Scale Biomass Co-firing for PC Combustors, Freeman, M.C. et al. Proceedings of Advanced Coal-Based and Environmental Systems Conference, DOE/FETC, Pittsburgh, PA, July 22-24,1997 Increased Flame Length w/ increased Biomass Content 12
Accurate Simulation of Gasification CO Challenge Ensure complete Combustion Study different Fuels/Loads Accurately predict Thermal Loading ANSYS Solution Realizable k- Turbulence Model Finite Rate/Eddy Dissipation Model Coal Calculator Results Impact of Inlet Positions was studied Impact of Fuel Change was studied Temperature H 2 H 2 O 13
Design of a T-fired Boiler Industry Std. OFA (Columbia Unit 1) NO x reduction Flue gas streamline density is high in near nose region Utilization factor of the upper furnace is low SmartBurn OFA (Columbia Unit 2) Beyond NO x reduction Flue gas streamline density is evenly distributed at the nose level Utilization factor of the upper furnace is increased (superheater division panels) Courtesy of SmartBurn, LLC. 14
Innovative Pollutant Model: Time-Scale Separation for CO R13 - BETA 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 DY Dt CO Y CO formation at the flame front front CO s T c Oxidation CO CO 2 c S CO Diffusion 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 15
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) Results Fast Simulation CO Predictions are in agreement with Experimental Results Geometry Accurate Boundary Conditions CFD Prediction of Partload CO Emissions using a Two- Timescale Combustion Model - GT 2010-22241 Comparison with Experimental Data 16
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 Blow-Off or Flashback Scale Resolving Models proved to be more accurate State of the Art Scale Resolving Models in ANSYS CFD Scale Adaptive Simulation Detached-Eddy Simulation Delayed Detached-Eddy Simulation Embedded Large-Eddy Simulation Large-Eddy Simulation 17
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 18
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 Pilot Burner Main Burner Double Skin Impingement Cooled Combustor PreChamber Radial Swirler Prediction of Aerodynamic Frequencies in a Gas Turbine Combustor Using Transient CFD - GT2009-59721 19
Newly Implemented Finite-Rate Unsteady Combustion Model: Thickened Flame Model R13 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 20 Flame/Turbulence Interaction: Efficiency function Accurate Flame Representation
Newly Implemented Premixed Unsteady R13 Combustion Model: G-Equation In Unsteady Mode, typical Premixed Model can predict a dissipative thick flame surface Affect accurate prediction of flame surface/turbulence interaction Degrades quality of the results REACTANT PRODUCTS 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 21
The Full Power of ANSYS Workbench: Optimization, FSI, etc. ANSYS Mechanical Design Optimization Examples: Optimize a geometry Optimize operating conditions Gas temperature 1-way coupling Total deformation wall temperature ANSYS CFD 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 22
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