ansys combustion analysis solutions - overview …...ansys workbench – fluid structure interaction...

© 2011 ANSYS, Inc. September 14, 2011

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ANSYS Combustion Analysis Solutions - Overview and Update

Gilles Eggenspieler ANSYS, Inc.


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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

Agenda


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Combustion Modeling

Dispersed Phase Models

(Solid/liquid fuels)

Droplet/particle dynamics

Evaporation

Devolatilization

Heterogeneous reaction

Radiative Heat

Transfer Models

Mass

Momentum + Turbulence

Energy

Chemical Species

Governing Transport

Equations

Pollutant Models

NOx

SOx

Soot

Infinitely fast chemistry

Da >> 1

Finite rate chemistry

Da ~ 1

Reaction Models

- Eddy Dissipation model

- Premixed model

- Non-premixed model

- Partially premixed model

Reaction Models - Laminar Flamelet model - Laminar Finite rate model - EDC - Composition PDF

Turbulence models LES RANS k-epsilon k-omega RSM…..


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An ANSYS Solution for every Simulation Challenge

High Quality Fuel/Air Mixing

Liquid Fuel Injection

Complex Chemistry

Emission Predictions

Heat Transfer Computation

Configuration Optimization

Lifing

Advanced Turbulence Models (RANS, SAS, LES)

DPM tracking, Advanced Break-Up Models

Complete Array of Turbulent Chemistry Models

Post-Processing and Coupled Pollutant Models

Advanced Wall Functions and Turbulence Models

Parametric Simulation, Design Exploration

Fluid-Structure Interaction, ANSYS FEA, nCode


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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

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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

Premixed Combustion

Progress Variable Flame Speed Models - Zimont Flame Speed - Peters Flame Speed Enhanced Coherent Flame Model Compressibility Effects Non-Adiabatic Systems

R13

=

Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing

Decoupled Detailed Chemistry - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady Post-Processing

R13


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Accurate Emission Prediction: GE LM 1600

Geometry

Mesh

Temperature

NO Predictions

• 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.


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Furnaces Retrofit

Before air staging

After air staging

• Challenge

– Pollutant Control

– Stable Flame under different Load

– Minimize Wall Erosion

– Determine Optimum Air Staging

• ANSYS Solution


– Laminar Flamelet model

– SNCR Local NOx Reduction

• Results

– Downtime due to trials-and-errors was avoided

– Effect of multiple Staging Approaches was studied

– Optimal Air Staging was determined

Courtesy of Babcock Power, Inc


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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

Post-Processing Pollutant Models - NOx - SOx - Soot Steady and Unsteady Post-Processing

Decoupled Detailed Chemistry - Pollutant Finite-Rate Chemistry added on-top of the existing simulation - Pollutants and Minor Species only Steady and Unsteady Post-Processing

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Composition PDF Transport (Chemistry/Turbulence Interactions)

KEY TECHNOLOGY: CHEMISTRY ACCELERATION


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Efficient Chemistry Acceleration

From 2 to 10’s of Species

Stiff Reaction Rates

Minor Species and Radicals Challenge

Chemistry Computation Cost >> Fluid Computation Cost

Chemistry Agglomeration

In-Situ Adaptive Tabulation (ISAT)

R13

Dimension Reduction

Decoupled Detailed Chemistry

R13

R13

Solution


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Efficient Chemistry Acceleration

IN-SITU ADAPTIVE TABULATION Store Reaction Mappings in an ISAT table Retrieve Reaction rates when needed Up to 100 Speed-Up Factor

CHEMISTRY AGGLOMERATION

Agglomerate cells of similar Composition Call ISAT on Agglomerated Cells Map Reaction Step back to Original Cells

DIMENSION REDUCTION

User selects the transported Species Calculate the remaining unrepresented species using constrained chemical equilibrium Allows 50+ species in the full mechanism

DECOUPLED DETAILED CHEMISTRY

Slow chemistry (pollutants) - NO - CO Compute Chemistry (Minor Species) on a frozen (Fluid/Major Species) Field

R13

R13 R13


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Retrofitting a 820 MW Power Station

• Challenge

– Retrofit a Power Combustion System to Oxy-Fuel Combustion

– Maintain Temperature Distribution

• ANSYS Solution


– 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

“Development of Oxy-fuel Combustion Technology for Existing Power Plants”, Song Wu, et al.

Courtesy: Wu et al, Hitachi Power Systems America, Ltd

Temperature

O2 volume fraction


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Studying BioMass Combustion

Increased Flame Length w/ increased Biomass Content

(*) “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

• Challenge

– Study a BioMass Combustion Chamber

• ANSYS Solution



– Discrete Phase Injection

• Results

– Flame Length increase with the amount of BioMass Content

– Delayed Combustion for large Particles

– Validation using Freeman et al. data *


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Accurate Simulation of Gasification

Temperature

CO

H2

H2O

• Challenge

– Ensure complete Combustion

– Study different Fuels/Loads

– Accurately predict Thermal Loading

• ANSYS Solution


– Finite Rate/Eddy Dissipation Model

– Coal Calculator

• Results

– Impact of Inlet Positions was studied

– Impact of Fuel Change was studied


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Design of a T-fired Boiler

SmartBurn® OFA (Columbia Unit 2) • Beyond NOx reduction • Flue gas streamline density is evenly

distributed at the nose level • Utilization factor of the upper furnace is

increased (superheater division panels)

Industry Std. OFA (Columbia Unit 1) • NOx reduction • Flue gas streamline density is high in near

nose region • Utilization factor of the upper furnace is

low

Courtesy of SmartBurn, LLC.


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Innovative Pollutant Model: 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

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

R13 - BETA

CO formation at the

flame front

DiffusionSccsYDt

DYCOT

front

COCO

Oxidation

CO CO2


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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

CFD Prediction of Partload CO Emissions using a Two-Timescale Combustion Model - GT 2010-22241

Geometry

Accurate Boundary Conditions

Comparison with Experimental Data


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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


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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


– State of the Art Turbulence Models (LES)

– State of the Art Combustion Models (Premixed Model)

• Results


– Accurate Prediction of Velocity Fields


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Scale Resolving Methods for Combustion Dynamics: SAS Example (Siemens – Dual Fuel DLE)

Double Skin Impingement Cooled Combustor Main Burner

Pilot Burner

PreChamber

Radial Swirler

Prediction of Aerodynamic Frequencies in a Gas Turbine Combustor Using Transient CFD - GT2009-59721

• Challenge

– Simulating Combustion Processes in a Gas Turbine Combustion Chamber

– Predict the Combustion Dynamics

• ANSYS Solution


– Advanced Turbulence Models (SAS)

• Results


– Accurate Prediction of the Acoustics Behavior of the system


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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

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

Dynamic Thickening

in the reaction zone

Local Thickening Factor as

a function of the mesh size

Flame/Turbulence Interaction:

Efficiency function Accurate Flame

Representation

R13


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Newly Implemented Premixed Unsteady 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

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

G-Field: Distance from the flame (Here

burnt region where G > 0)

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PRODUCTS REACTANT

REACTANT PRODUCTS

Thin Flame


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The Full Power of ANSYS Workbench: Optimization, FSI, etc.

Equivalent elastic strain

Gas temperature

wall temperature

Total deformation 1-way coupling

ANSYS CFD

ANSYS

Mechanical

ANSYS Workbench – Fluid Structure Interaction (FSI)

– Couples CFD and Structural Simulations

– Transfer Pressure Loads, Temperature Loads, CHT data, etc.

– 1- and 2-way FSI

Design Optimization – Examples:

– Optimize a geometry

– Optimize operating conditions


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ansys combustion analysis solutions - overview …...ansys workbench – fluid structure interaction...

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