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Exploring STAR-CCM+ Capabilities, Enhancements and Practices for Aerospace Combustion Niveditha Krishnamoorthy CD-adapco

Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

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Page 1: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Exploring STAR-CCM+ Capabilities, Enhancements and Practices for

Aerospace Combustion

Niveditha Krishnamoorthy

CD-adapco

Page 2: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Overview of modeling capability

Applications, Practices and Enhancements

– Gas Turbines

– Rocket Nozzles

– Scramjets

Summary

Outline

Page 3: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Density – and Pressure- based flow

solvers

Incompressible through hypersonic flow

regimes

Full range of turbulence models

– RANS, LES and DES

Multi-physics

– Combustion

– CHT

– Fluid-Structure Interaction

– Aeroacoustics

Overview – (1)

Page 4: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Combustion and Emissions Modeling

– Models for different flame types: Premixed,

non-premixed and partially premixed

– Multi-component liquids, solids and gases

– Homogeneous and Heterogeneous

chemistry

– Global, tabulated chemistry,

reduced/detailed chemistry

– Emission models for Soot, and Nox

• Soot

– Two –equation semi-empirical model

– Method of moments

• Nox

– Fuel

– Prompt

– Thermal

Overview – (2)

Mass Fraction of CO (LES run)

Page 5: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Participating Media Radiation Model

Overview –(3)

• Radiative Transport Equation (RTE) solved using the Discrete Ordinates Method (DOM)

• S2 to S16 Quadratures available

Properties of the medium:

• Gray Thermal Radiation

• User defined

• Weighted Sum of Gray Gases

• Multiband Thermal Radiation

• Properties in wavelength bands

• Particle Radiation

• Scattering: isotropic, gray

• Absorption: gray

Page 6: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Application, Practices and Enhancements

Gas Turbine Combustors

Page 7: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Gas Turbine Combustor

Emissions Fuel Flexibility,Flame Stability

Thermo-acoustic Instability

Mechanical Durability Cost

• UHC• Soot• Nox• CO

• Flame shape• Flame location• Flash-back/ blow-off• Gaseous/liquid Fuels

• Liner temperature• Component temperature

System Level

Combustion Chemistry Heat TransferFluid Dynamics

Unit Level

• Flow and mixing• Swirlers• Bluff bodies

• Fuel formulation• Operating conditions• Chemical kinetics• Thermodynamics

• Conduction• Convection• Radiation

Page 8: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Liquid Droplet Combustion

– Droplet Evaporation• Quasi-steady• User defined

– Droplet Break-up• Primary atomization

– Linear Instability Sheet Atomization (LISA)

• Secondary break-up– Kelvin Helmholtz-Rayleigh Taylor (KHRT)– Taylor Analogy (TAB)– Stochastic Break-up (SSD)

– Droplet Wall-impingement• Bai-Gosman• Satoh

– Collision Detection Model• No Time Counter (NTC)• O’Rourke

– Two-way Coupling

– Turbulence Dispersion• Random Walk Technique

Combustion Chemistry: Models

Page 9: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Global Chemistry– Global multi-step reactions can be calibrated for specific operating conditions

– Calibration carried out using HEEDs and DARS-Basic

[ Freely propagating Flame]

Gas Phase Combustion Modeling

𝜔 = 𝑨𝑒−𝐸𝐴/𝑅𝑇 𝐶 𝒏 𝐷 𝒎

𝐶 + 𝐷 → 𝐸 + 𝐹Sample Reaction:

Reaction Rate:

Variables we can vary

• A : Pre-exponential Factor

• n, m : FORD (forward reaction rate exponents)

Calibration to match flame speed

Blue = Literature

Red = uncalibrated

Green = Calibrated

Purple = Hand Calibrated

5 Step Mechanism

Page 10: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Tabulated Chemistry

– Presumed Probability Distribution Models (PPDF Flamelet)

• Update PPDF Species once per time step without affecting results

• Can delete species not needed for post-processing: affects table size and look-up

times

• Vectorial table retrieval and more efficient table interpolation

– Flamelet Generated Manifold (FGM)

• Flexible definition of progress variable

• Transports progress variable and its variance. Better representation of state-space

than the traditional progress variable model

• Inclusion of heat loss effects in the table always ensures species and enthalpy are

consistent

Gas Phase Combustion enhancements

Page 11: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Performance Improvements: Large Cases (LES)

• Flow Solver improvements in v9.04

Case 1 Case 2

Case 1 Case 2

•Combustion solver improvements in

v9.02 (40-50% speedup)

•Flow and Lagrangian solver

improvements in v9.04

(20-25% speedup from v9.02)

Page 12: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Accurate temperature distributions are required for emission predictions and to assess component life

Heat transfer in solid components requires adequate description of

– Conduction

– Convection

– Radiation

Liners can either be modelled as shells (1-D heat conduction) or with 3-D heat conduction

Heat Transfer

Page 13: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Import CAD

– Single or multiple injectors

– Liners can have all details like dilution holes, effusion holes

– All solid components can be included: splash plate, dome etc.

Repair the CAD to get a closed geometry

Extract fluid domain and all the solid components from the closed CAD

Refine prism layer mesher for CHT components such that Y+ is close to

1

General Meshing Procedure for CHT

Page 14: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Need to ensure there are no

intersecting parts or gaps

between components

Fully conformal mesh possible

Quality of mesh can be checked

by running mesh diagnostic

report

Checks for:

– Face Validity

– Cell quality

– Volume change statistics

– Cell and boundary skewness

angle

Meshing

1:1 matching

Conformal mesh

Page 15: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Lagrangian update can be done once every time-step

Dynamic load balancing for Lagrangian spray helps with speed up

Update species and radiation once per time-step (for LES runs)

Other useful settings

Page 16: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Application, Practices and Enhancements

Rocket Nozzles

Page 17: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Combustion Chamber

– Multicomponent Droplet combustion

– Real Gas Equation of State

– Equilibrium and finite rate chemistry models

Nozzle Flow/Plume Study

– Coupled Solver

– Equilibrium or finite rate chemistry

Heat Transfer (CHT)

– Base heating

– Film Cooling

Application Areas

Page 18: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Combustion with Real Gas Model

Fuel: Methane at 275.8 K

Oxidizer: Oxygen at 105.9 K

Solver:

3D, Steady, k-omega SST

Redlick Kwong EOS,

Coupled Implicit with solution driver

and convergence accelerator (CCA)

Non-premixed, non-adiabatic PPDF

Page 19: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Coupled Implicit, Axisymmetric

Steady, SST K-Omega turbulence

Detailed chemistry: 11 species

DARS-CFD Approximation options:

– In-situ Adaptive Tabulation

• Populates source terms as the

simulation progresses for

subsequent look-up

• Speeds computational time once the

table is populated

– Equilibrium Time-Scale

• Quick approximate solution for

detailed chemistry calculations

• Assumes chemical composition

relaxes to local equilibrium

composition at time-scale

determined by flow and chemistry

Reacting Nozzle Flow

Page 20: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

One stream or part of one-stream is

inert, its reactivity neglected

Sole effect of inert stream is to dilute

reacting products

Transport equation solved for

corresponding mixture fractions

Species mass fractions computed as

linear combination from inert stream

and reacting streams

Faster table generation and

interpolation. Smaller table size

Inert Stream model for PPDF Combustion

Yi=Zinert*Yi_inert+(1-Zinert)*Yi_reaction

Page 21: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Application, Practices and Enhancements

Scramjets

Page 22: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Density-based Solver

– Coupled, implicit formulation with

AMG acceleration

– TVD reconstruction

• AUSM+ or Roe inviscid flux schemes

• MUSCL + Venkata limiter

– Advanced initialization and

convergence control

– Real gas models

• Redlich Kwong

• Soave-Redlich Kwong

• Modified Soave-Redlich Kwong

• Peng Robinson

• EBU, PPDF combustion models

High Speed Reacting Flows

Page 23: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Advanced Initialization

– Grid sequencing option

– Fully implicit newton-type solution algorithm

– Controllable number of coarse levels

Continuity Convergence Accelerator (CCA)

– Used for high speed flows where convergence for mass flow is slow

– Solves pressure correction equation using density based Riemann Flux

discretization

– Overall and individual cell mass imbalances are minimized at each iteration

– Option available for Coupled Implicit Solver.

Advanced Initialization and Convergence Control

Page 24: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Supersonic Combustion

• H2 Fueled NASA SCHOLA direct-connect Scramjet engine

• Validate against experiment and NASA VULCAN code

Mesh:

1.4M Hex-dominant

10 Prism Layers

Solver:

Density based solver

Steady,k-w SST, AUSM+FVS

Non-adiabatic PPDF

Page 25: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Supersonic Combustion (2)

Page 26: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Global Chemistry

– Single or multi-step

– Variants of eddy break-up model

• Standard

• Hybrid

• Combined time-scale

• Kinetics only

Tabulated Chemistry

– PPDF Equilibrium

Detailed Chemistry

– DARS-CFD stiff chemistry solver

– Use Equilibrium Time-Scale

approximation for initial guess

– Then switch to finite rate chemistry

• Laminar flame concept

• Eddy dissipation concept

Combustion Modeling in Scramjets

Dual Mode Scramjet

Page 27: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Meshing

– Utilize extruded (directed) mesh as much as possible in long, non-complex,

ductwork (isolator, combustor, etc.)

– Use directional reordering of mesh in streamwise direction

Coupled Flow and Energy

– Coupled inviscid flux scheme: AUSM+

– Coupled Energy: Enable Enthalpy Formulation

Boundary Conditions

– Specify fuel inlets as mass flow. Ramp flow rate over 1000 iterations

– Pressure outlets can have a small area of extrusion w/ free slip wall

General Tips for Scramjets

Page 28: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Solver Settings for Scramjets

Coupled Implicit– CFL = 5.0

– Ramp CFL from 0.1 over first 300 iterations

AMG Linear Solver– Max Cycles = 10

– V-Cycle:

• Pre-Sweeps = 1

• Post-Sweeps = 3

• Max. Levels = 50

Grid Sequencing Initialization– 10 Levels, 150-250 iter./level, Tolerance = 0.005, CFL = 5.0

Expert Driver– CFL Ramp:End Iteration = 250

– Min. Explicit Relaxation = 0.35

– Max. Explicit Relaxation = 0.75

– Target AMG Cycles = 6

Continuity Convergence Accelerator– URF = 0.6 (Ramp from 0.03 over first 100 iterations)

– Enhanced Mass-Imbalance Calculations Enabled

– AMG Solver Convergence Tolerance = 0.05, V-Cycle: 1 Pre-Sweep, 1 Post-Sweep, Max levels = 50

Page 29: Exploring STAR-CCM+ Capabilities, Enhancements … · Exploring STAR-CCM+ Capabilities, Enhancements and Practices for ... Redlick Kwong EOS, ... • Soave-Redlich Kwong

Multi-physics simulations involving high speed flows, reactions and heat

transfer possible using STAR-CCM+

Continued efforts on making the code faster for complex flows

Best practices established for:

– Meshing

– Physics set-up

– Solver settings

– Initial and boundary condition specifications

In each area of application across industry sectors

Summary