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© Dacolt 2009 2011 www.dacolt.com Dacolt is a trading name of Dacolt International BV, registered under number 14082157 at the Dutch chamber of commerce. Advanced combustion modelling with ANSYS ® FLUENT ® and Tabkin ® F.A. Tap and P. Schapotschnikow ANSYS Belgium Conference 2011 [email protected]

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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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Set-up look-up table calculation

© Dacolt 2009 – 2011www.dacolt.com

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Analyse look-up table

© Dacolt 2009 – 2011www.dacolt.com

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Download look-up table and run CFD

© 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

15

CFD results: auto-ignition delay

© Dacolt 2009 – 2011www.dacolt.com

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CFD results: flame lift-off

© Dacolt 2009 – 2011www.dacolt.com

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CFD results: heat release modes

© 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]