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Reacting Flow Modeling in STAR-CCM+
Rajesh Rawat
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Latest Additions (v 7.02/v 7.04)
Eulerian Multi-phase Reaction Model
Soot Model – Moment Methods
PPDF Flamelet
– Multi-stream model
Complex Chemistry Model (DARS-CFD)
– EDC (additional modifications)
– Dynamic Load Balancing
– ISAT
Further enhancements and testing for LES
Best Practices for LES
Misc – Non-transported Passive Scalars
– Permeable fixed flux or fixed species Boundary Conditions
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Lagrangian Multiphase Capabilites
Particle radiation
Multi-component droplet evaporation
General Particle Reactions
erosion models
Injector Models
– Part, Point, Hollow Cone and Surface Injectors
Primary Atomization Model
– Pressure Swirl Injector (Lisa model)
Secondary Breakup Model
– KHRT
– Reitz-Diwakar
– TAB
Inner Angle
Outer Angle
Origin
Axis
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Particle Reaction Model
Particle Reaction Model is available through Lagrangian Multiphase
framework of STAR-CCM+
Two Reaction Models are available: Particle Devolatilization and Particle
Combustion
Can simulate
– Particle Devolatilization, Sublimation, Melting
– Particle Combustion, Oxidation, Pyrolysis
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Particle Combustion
In particle combustion modeling, a solid particle reacts with a gas-phase
species to form solid and/or gas-phase products
Three different methods are available for specifying the reaction rates:
– First Order Combined Rate
– Half Order Combined Rate
– User-Defined Rate
The combined rate considers gas-species diffusion to the particle. The
Diffusion Coefficient can be specified by the user as scalar profile.
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Example Reactions
Particle Devolatilization Model
-- CaCO3 CaO + CO2
Particle Combustion Model
-- 2Ca (s) + O2 (g) 2CaO (s)
-- NaOH (s) + HF (g) NaF (s) + H2O (g)
-- Fe2O3 (s) + 3H2 (g) 2Fe (s) + 3H2O
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7
LES
•All Yplus treatment
•Second order implicit time differencing
•Both CD and BCD
•Non-reflecting boundary condition
•Synthetic turbulence for inflow BC
•Reacting Flow
• Thickened Flame Model
• Algebraic Variance and SDR
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Sandia D Flame
Mesh count: 4.1 M
Polyhedrals in the vicinity of inlet
Extruded Polyhedrals elsewhere
Volumetric control in the flame region
Approximately 0.18 mm of mesh size in radial direction
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Temperature – Instantaneous & Mean
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Movie - Temperature
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Comparison with Experiment – Centerline Axial
Velocity
RMS Axial Vel
Mean Axial Vel
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Comparison with Experiment – Centerline Mixture Fr
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LES Best Practices
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Library Based Models
STAR-CCM+
Transport Equations
H298 Source Term
Premixed Flame (CFM)
Properties
Emissions source terms (Nox/soot)
PVM/Flamelet Library
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The progress variable model
15
• A precomputed table is used to store the effects of detailed chemistry on combustion: selected species, source term to chemical enthalpy, mixture NASA polynomials, and molecular weight
• The combustion state is described using a progress variable based on chemical enthalpy
• h298 is the chemical enthalpy for the mixture, while h298|c=0 and h298|c=1 are the chemical enthalpies at the initial conditions and equilibrium state, respectively.
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Premixed Gas Turbine
PVM
DARS-CFD with GRI-Mech
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Temperature Comparison
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Soot Model Validation
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Centerline Temperature Profile
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Centerline Soot Profile
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Radial Profiles for Soot (x = 0.347)
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Soot Distributions
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Multi-Stream PPDF
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Temperature & Lagrangian Tracking
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Complex Chemistry
• Can read Chemkin format and no limit on number of species
• Online tabulation using ISAT is available
– Factor of 2-5 speedup is commonly observed
• Dynamic load balancing is available to achieve scalability for chemistry
calculation with large number of processors.
• DARS-Basic provides tool to reduce the chemistry that can be imported in
STAR-CCM+ for further speedup for complex chemistry calculations.
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Dynamic Load Balancing
0
20
40
60
80
100
120
140
Dynamic balancing
Tim
e (h
ou
rs)
Transient run
Transient run with load balancing
8p
16p
32p
Same non-premixed flame but with more detailed mechanism with 53 species tested for transient run
Presented: complex chemistry CPU time after 200 iterations
130 Hrs
60 Hrs
25 Hrs
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The EDC model
27
• The total space is divided into two zones
Fine structures
All the chemical reactions takes place
Represents the smallest turbulence scales
Bulk structure
No reactions occur
• The sub-grid chemistry scales don't need to be resolved at a cell level.
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Fine structures
28
• Governing equations for the species and enthalpy
*: quantities in the fine structure
<>: the cell mean values.
• The residence time: how long the species remain in the fine structures
• Mass fraction of fine structures in the cell:
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Temperature Profiles
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CH4 Profiles
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SCR
• Flow Direction is from left to right
• Solid Cone Spray with 70o, not much
turbulent dispersion
• Thermolysis consumes Urea quite rapidly
• Conversion Efficiency & Uniformity Index of
NH3 and H2O can be deduced from this
analysis.
• This can help optimize injection strategy for
UWS upstream of SCR system.
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Results – NOx Reduction Comparison
Two-Step Model
Detailed Surface Chemistry
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Conclusions
Eulerian Multi-Phase with Reactions
LES effective but expensive
Finite-rate kinetics
– Library-based
– Direct chemistry coupling
Speedup
– Load balancing
– Clustering
– ISAT