ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
TEKES project 40190/05
Antti Oksanen, project leader, Tampere University of Technology
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
1
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Backgrounds
• Financing
ÆTekes
ÆKvaerner Power Oy, Andritz Oy, Vattenfall Utveckling Ab
• Budget 418 k€
• Period 2005-2006
• Participants (researchers)
ÆTUT, Institute of Energy and Process Engineering (Satu Palonen, Ville
Tossavainen)
ÆHUT, Laboratory of Applied Thermodynamics (Petri Majander)
ÆÅbo Akademi, PCC, Combustion and Materials Chemistry (Anders Brink)
ÆStanford University, Research Group of Computational Energy Sciences
(CES), USA, Prof. Heinz Pitsch
ƒ A part of Flow Physics and Computation Division, closely connected to
¾ Turbulence Research Center and
¾ Center for Integrated Turbulence Simulations
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
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ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Aim of the Research
• To give better description and understanding of the interaction
between chemistry and turbulence Î university LES (Large Eddy
Simulation) code (TUT)
• To apply for emission formation and SNCR (Selective Non-Catalytic
Reduction) process with detailed experimental techniques (TUT)
• The experiments provide validation data for LES computations (TUT)
• To study the reduction phenomenon of nitric oxide and ammonia
with LES turbulence modelling in laboratory reactor environment Î
comparison also with RANS computations (TUT)
• To model the reactor flow conditions without combustion using TKK
LES code (TKK)
• To model the flame experimentally well studied using LES and RANS
of commercial code (ÅA)
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
3
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Pilot Reactor (TUT)
• Burner
ÆOilon GP-6.20H: 60-160 kW
ÆFuel: Liquefied petroleum gas, LPG
• Dimensions of the reactor
ÆInside cross section: 400 × 400 mm2
ÆOutside cross section: 760 × 760 mm2
ÆTotal height: 2830 mm
• Air splitting
ÆPrimary/secondary air: 70 %/30 %
• Secondary air system
Æ8 pipes in both sides
Æ3 pipe diameters: 8, 10, 12 mm
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
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ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Pilot Reactor Measurements (TUT)
• LDA (Laser Doppler Anemometer)
ÆTwo velocity components
• Concentrations
Æ22 measurements points at the reaction zone
• Temperature measurements
ÆK-type thermocouples
• Flow rates
ÆPrimary and secondary air
ÆNO and NH3
ÆFuel
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
5
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
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Computational Domains of Pilot Reactor (TUT)
Pilot reactor in vertical direction
Pilot reactor in horizontal direction
RANS simulations
Secondary air pipes
LES simulations
Earlier LES
simulations
© Satu Palonen
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
• Contribution is to model reactions between nitric oxide and
ammonium (SNCR-process) using LES turbulence modelling
(Stanford code)
• Computational flow cases:
ÆCASE 1: Cold flow without reactions
ÆCASE 2: Reactive flow with substoichiometric primary air and staged
secondary air feeding
ÆCASE 3: Reactive flow with added nitric oxide (NO) and ammonium (NH3)
feedings Æ main contribution of the research
• Each case is studied with three different jet mass flow rates
(ReD = 10000, 12000 and 15000)
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
7
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
• Both traditional RANS (Reynolds Averaged Navier-Stokes) and LES
computations are performed
• RANS simulations:
ÆWhole turbulence length scale is modelled
ÆComputations made with commercial FLUENT 6.2 software
• LES simulations:
ÆLarge scales are solved and small scales modelled
ÆLES computations are performed with academic code ”CHARLES”
developed at Stanford University
ÆTurbulence-chemistry interaction is based on laminar flamelet model
ÆResults are validated against experimental data from Osbourne pilot
reactor at TUT
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
8
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
Stanford Structured LES Code ”CHARLES” [1]
• Based mainly on Charles Pierce’s PhD work
(http://www.stanford.edu/group/ctr/pdf/charles_pierce_thesis.pdf)
ÆSolves 3D (cartesian/cylinder) turbulent flow using
Large Eddy Simulation with dynamic subgrid-scale
model (Germano et al., 1991)
ÆChemistry/turbulence–interaction is modelled with
fast chemistry, steady flamelets or progressvariable/unsteady flamelet models
ÆCurrently problems to run parallel jobs using more
than two processors
Velocity iso-surface
colored by pressure
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
9
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
Stanford Structured LES Code ”CHARLES” [2]
• Wall boundary conditions were modified to
take into account secondary air inlets
ÆMultiple round inlets will be inserted with
velocity profiles
ÆCurrent velocity boundary conditions are
stationary
• Implementation of test case
ÆMain flow Reynolds number Remain = 5000
(Ujet = 2 x Umain)
Æ128 x 64 x 64 mesh (~ 2 x 1 x 1)
Æ2000 time steps ~ 30 minutes computation
on 2 CPUs
Institute of Energy and Process Engineering
Antti Oksanen
Instantaneous y-velocity iso-surface
colored by pressure
10.2.2006
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ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
RANS Computations [1]
• Several different mesh constructions were build for the reactor for comparison
• Results of hex-core (hybrid) meshes were poor
ÆUnstructured cells near walls make jets behave unphysical
Contours of x-velocity, 3rd jet from wall (d=8mm)
Institute of Energy and Process Engineering
Contours of x-velocity, 3rd jet from wall (d=12mm)
Antti Oksanen
10.2.2006
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ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
RANS Computations [2]
• Block-structured grid was build around one secondary air jet
ÆGood accuracy, but too complex for total 16 jets Î this approach was abandoned
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
12
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Numerical Simulations in Pilot Reactor (TUT)
RANS Computations [3]
• Present grid consists of several non-conformal (Chimera) meshes
which is a good compromise between grid size and accuracy
Grid interface
Closer look of non-conformal mesh near secondary jet
Non-conformal grid interfaces
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
13
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
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Multiple Opposing Jets in a Cross-Flow (TKK)
• Inert Large Eddy Simulation of Osbourne reactor flow with TKK code
• Three opposing pairs of jets included
2m
V
U
0.4 m
V
Scalar contours
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
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Multiple Opposing Jets in a Cross-Flow (TKK)
•
•
•
•
Current mesh includes 4 million control volumes
The flow possesses large range of scale Æ a challenging case
IBMSC parallel computer of CSC applied
Figure below illustrates penetration of secondary air in main flow
Secondary air pipes
Momentum flux in a
secondary air pipe
Contours of mass (50%)
coming from pipes
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Test Case: Sandia Flame D (ÅA)
Dimensions:
Main jet:
Nozzle diameter = 7.2 mm
Pilot diameter = 18.2 mm
25% CH4, 75% air
Reaction kinetics: LES&RANS
Scalar Measurements: Raman/Rayleigh/LIF
measurements of F, T, N2, O2, CH4, CO2, H2O,
H2, CO, OH, and NO were obtained with a
spatial resolution of 0.75 mm.
Velocity Measurements: Two-component LDV
measurements were carried out at the Technical
University of Darmstadt.
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
16
ADVANCED TURBULENCE MODELS FOR
EMISSION MODELLING IN GAS COMBUSTION
Test Case: Sandia Flame D (ÅA)
Conclusions:
• LES temperature predictions in better agreement with measurement
than RANS
• Both models with 4-step chemistry over-predict CO mass fraction
• LES computing time >1000 CPU hours (~0.1 s), statistics collected
for 100 CPU hours, too short!
• RANS computing time ~ 1 CPU hour
• LES only motivated for advanced application (complex chemistry,
time dependent applications)
Institute of Energy and Process Engineering
Antti Oksanen
10.2.2006
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