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© Dacolt 2009 – 2011www.dacolt.comDacolt is a trading name of Dacolt International BV, registered under number 14082157 at the Dutch chamber of commerce.
Advanced combustion modellingwith ANSYS® FLUENT® and Tabkin®
F.A. Tap and P. Schapotschnikow
ANSYS Belgium Conference [email protected]
© Dacolt 2009 – 2011www.dacolt.com
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Contents
• Introduction
• Tabkin software for CFD look-up tables
• Dacolt PSR+PDF combustion model
• Integration with ANSYS FLUENT 12.1
• Validation study: lifted n-heptane spray flame
• Industrial application: main burner for sulphur recovery unit
• Summary and outlook
© Dacolt 2009 – 2011www.dacolt.com
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About Dacolt
Dacolt offers software and services for CFD modeling of industrial combustion applications
• Services:– CFD consultancy
– Software development
• Software:– Tabkin®
– Combustion Web Apps
• About Dacolt:– Based in Maastricht, the Netherlands
– ‘Enhanced Solutions Partner’ of Ansys, Inc.
© Dacolt 2009 – 2011www.dacolt.com
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Combustion & CFD
• Large difference in time and length scales between flow and chemistry
• CFD codes typically resolve the flow scales
• Sub-grid modeling required for:
– Combustion chemistry
– Interaction between turbulence and chemistry
• Detailed chemistry required for:
– Combustion physics: auto-ignition in Diesel engines, knock in SI engines, flash-back in gas turbines, lifted flames in industrial burners, ...
– Pollutant emissions: NOx, soot, CO, ...
• Observed trends in combustion modeling:
– Recent models use CFD look-up tables (FGM, FPI, ECFM-{3Z,CLEH}, ...)
– Increasing complexity of reaction mechanisms
Look-up tables for combustion chemistry: Detailed chemistry effects and turbulence interaction with low CPU overhead
Diesel engine simulation, courtesy of PSA Peugeot Citroën
© Dacolt 2009 – 2011www.dacolt.com
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Use of CFD look-up tables in advanced combustion models
1. Chemical reactions are computed upfront and stored in look-up table
2. Combustion look-up table is read by CFD code
3. Chemical reactions are interpolated from look-up table during CFD simulation
Computational effort for
chemistry done prior to CFD simulation
© Dacolt 2009 – 2011www.dacolt.com
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Dacolt introduces Tabkin®
• Software-as-a-Service package for generation of CFD look-up tables
• Features:
– Easy and powerful user interfaces
– Robust solvers
– Table visualisation
– Various combustion model exports
– Scalable CPU resources
Turn-key solution for CFD look-up tables for ANSYS FLUENT
© Dacolt 2009 – 2011www.dacolt.com
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Advanced combustion model using Tabkin: Dacolt PSR+PDF
• An advanced combustion model has been devised:– Using CFD look-up tables– Based on detailed chemical kinetics– Use of Tabkin in the CFD process
• Fields of application:– Steady-state: non-premixed and flameless burners– Unsteady: Diesel engines, HCCI, PCCI, SI engines knock, ...
• Features:– Progress variable / mixture fraction approach– Turbulence / chemistry interaction: presumed PDF– Complex chemistry model: homogeneous reactor
© Dacolt 2009 – 2011www.dacolt.com
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Implementation in Ansys Fluent 12.1
• Dacolt has partnered with ANSYS, Inc. to investigate the latest technologies for reactive flow CFD simulations
• Dacolt PSR+PDF offers detailed chemical kinetics at CPU cost comparable to standard equilibrium PDF model
• Efficient parallel implementation through UDFs
• Steady-state and unsteady variants
• Well-defined thermo-chemistry
© Dacolt 2009 – 2011www.dacolt.com
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Typical working cycle using Tabkin
(1) Secure login
(2) Set-up look-up table generation
(3) Look-up table generation is executed on cloud resources
(4) Download look-up table to local system and run CFD
(5) Visualise and analyse look-up table online
© Dacolt 2009 – 2011www.dacolt.com
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Lifted n-heptane spray flame from Engine Combustion Network (ECN)
• Test case (www.sandia.gov/ecn)– Constant-volume vessel, high-pressure spray injection– Diesel engine-like ambient conditions– Variation of ambient oxygen concentration
21, 15, 12, 10 or 8 vol-% O2
• CFD simulation– Turbulent, two-phase, reacting flow– 3D URANS CFD with ANSYS FLUENT 12.1– Auto-ignition, flame development
and stabilisation of a lifted flame – Dacolt PSR+PDF combustion model
• CFD look-up tables from Tabkin– n-heptane reaction mechanism– 500+ species, 2500+ reactions
• ECN video for 21% O2
108 mm
© Dacolt 2009 – 2011www.dacolt.com
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CFD results: typical ignition sequence
21 vol-% ambient oxygen concentration
t = 0.2 ms t = 0.35 ms(ignition)
t = 0.5 ms t = 1.0 ms t = 2.0 ms
Temperature contours
© Dacolt 2009 – 2011www.dacolt.com
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CFD results: flame structure
21% O2 15% O2 12% O2 10% O2 8% O2
Temperature contours after 2 ms
© Dacolt 2009 – 2011www.dacolt.com
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Industrial application
• CFD Consultancy for Duiker, the leading Dutch manufacturer of main burners for sulphur recovery units
• Dacolt PSR+PDF has been used to model key physics:
– Fast oxidation reactions and slow Claus reactions
– Flame lift-off
• 2D axi-symmetric and full 3D simulations on industrial scale
© Dacolt 2009 – 2011www.dacolt.com
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Summary
• Dacolt and Ansys have partnered for combustion model development
• An advanced combustion model named Dacolt PSR+PDF has been elaborated and implemented in ANSYS FLUENT 12.1
• Tabkin is used to generate the required CFD look-up tables for combustion chemistry
• A lifted n-heptane spray flame test case has been presented
• Key physics are captured for varying ambient O2 content:– Auto-ignition
– Flame lift-off
• Application of Dacolt PSR+PDF and Tabkin to industrial burners
© Dacolt 2009 – 2011www.dacolt.com
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Outlook
• Various test cases are under investigation at Dacolt:
– Diesel engine
– Delft Jet-in-Hot-Co-flow flameless burner
• Further integration of Tabkin with ANSYS FLUENT
• Enhancement of Tabkin with flamelet-based models
© Dacolt 2009 – 2011www.dacolt.comDacolt is a trading name of Dacolt International BV, registered under number 14082157 at the Dutch chamber of commerce.
Advanced combustion modellingwith ANSYS® FLUENT® and Tabkin®
F.A. Tap and P. Schapotschnikow
ANSYS Belgium Conference [email protected]