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

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• 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

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• 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

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• 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