Upload
others
View
9
Download
0
Embed Size (px)
Citation preview
Reacting Flow Modeling in STAR-CCM+
Rajesh Rawat
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
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
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
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.
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
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
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
Temperature – Instantaneous & Mean
Movie - Temperature
Comparison with Experiment – Centerline Axial
Velocity
RMS Axial Vel
Mean Axial Vel
Comparison with Experiment – Centerline Mixture Fr
LES Best Practices
Library Based Models
STAR-CCM+
Transport Equations
H298 Source Term
Premixed Flame (CFM)
Properties
Emissions source terms (Nox/soot)
PVM/Flamelet Library
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.
Premixed Gas Turbine
PVM
DARS-CFD with GRI-Mech
Temperature Comparison
Soot Model Validation
Centerline Temperature Profile
Centerline Soot Profile
Radial Profiles for Soot (x = 0.347)
Soot Distributions
Multi-Stream PPDF
Temperature & Lagrangian Tracking
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.
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
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.
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:
Temperature Profiles
CH4 Profiles
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.
Results – NOx Reduction Comparison
Two-Step Model
Detailed Surface Chemistry
Conclusions
Eulerian Multi-Phase with Reactions
LES effective but expensive
Finite-rate kinetics
– Library-based
– Direct chemistry coupling
Speedup
– Load balancing
– Clustering
– ISAT