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

Outli line Overvie view of mode deling ing capabi bility lity Ap Applications ations, , Practice tices s and En Enhan hance ceme ments nts – Gas Turbines – Rocket Nozzles – Scramjets Sum umma mary

Overvie view w – (1) 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

Overvie view w – (2) Combus ustion tion and nd Emissions ons Modeling ing – 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 Mass Fraction of CO (LES run) – Emission models for Soot, and Nox • Soot – Two – equation semi-empirical model – Method of moments • Nox – Fuel – Prompt Thermal –

Overvie view w – (3) Par Particip cipati ting ng Medi dia a Radiat ation ion Model del • 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

Applicati ication, on, Practices ctices and Enhanceme ncements nts Ga Gas Tur urbin bine Combu mbust stor ors

Gas Turbine Combustor System Level Fuel Flexibility, Thermo-acoustic Cost Emissions Mechanical Durability Flame Stability Instability • • • UHC Flame shape Liner temperature • • • Soot Flame location Component temperature • • Nox Flash-back/ blow-off • • CO Gaseous/liquid Fuels Unit Level Fluid Dynamics Combustion Chemistry Heat Transfer • • Fuel formulation Conduction • Flow and mixing • • Operating conditions Convection • Swirlers • • Chemical kinetics Radiation • Bluff bodies • Thermodynamics

Combustion Chemistry: Models 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

Gas Phase se Comb mbustion ustion Modelin ling Global al Chemistr try – Global multi-step reactions can be calibrated for specific operating conditions – Calibration carried out using HEEDs and DARS-Basic [ Freely propagating Flame] 5 Step Mechanism chanism Calibration to match flame speed Sample mple Reac action: ion: 𝐷 + 𝐸 → 𝐹 + 𝐺 𝜕 = 𝑩𝑓 −𝐹 𝐵 /𝑆𝑈 𝐷 𝒐 𝐸 𝒏 Reac acti tion on Rate: e: Variables we can vary • A : Pre-exponential Factor • n, m : FORD (forward reaction rate exponents) Blue = Literature Red = uncalibrated Green = Calibrated Purple = Hand Calibrated

Gas Phase se Comb mbust ustion ion enhancem emen ents ts Tabul ulat ated ed Chem emist stry – 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

Performanc ormance e Improvem ement nts: s: Large rge Cases ses (LES ES) • Flow Solver improvements in v9.04 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) Case 1 Case 2

Heat Transfer Accura urate temperatu perature re distr tribu ibuti tions ons are requi uire red d for emiss ssion ion predic dicti tions ons and to assess ess com ompone ponent nt life Heat t transf nsfer er in solid id compone ponents nts requi uire res adequate e desc scription ription of – Conduction – Convection – Radiation Liner ners s can eith ther er be mode delled led as shells lls (1-D (1 D heat at conduct nduction) ion) or with h 3-D heat at conduc nducti tion on

Genera eral l Meshing hing Procedure edure for CHT Impor mport t CAD AD – 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 ir the e CAD AD to get et a closed sed geom ometr try Ex Extract act flui uid d doma main in and all the e so solid d compon ponents ents from om the e closed ed CAD AD Refine ine prism m layer r mesh esher er for CHT compon ponen ents ts suc uch that t Y+ is close se to 1

Meshing ing Need to ensure there are no intersecting parts or gaps between components 1:1 matching Conformal mesh 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

Other er useful ful sett ettings ings Lagrang rangia ian up update e can be done ne once ce ever ery y time me-st step Dynami amic c load d balanc ncing ing for Lagrangi angian an spray y helps lps with th speed eed up up Update Up e species cies and radiat ation ion once ce per time me-st step ep (for or LES ES run uns) s)

Applicati ication, on, Practices ctices and Enhanceme ncements nts Rocket t No Nozz zzles les

Applica icati tion on Areas as Comb mbusti ustion on Chamb mber er – Multicomponent Droplet combustion – Real Gas Equation of State – Equilibrium and finite rate chemistry models Nozzl zzle e Flow/P w/Plu lume me Study udy – Coupled Solver – Equilibrium or finite rate chemistry Heat t Transf nsfer er (CHT) T) – Base heating – Film Cooling

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

Reacti cting ng Nozz zzle le Flow 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

Inert t Stream ream model el for PPDF DF Combust mbustion 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 Yi=Zinert*Yi_inert+(1-Zinert)*Yi_reaction Faster table generation and interpolation. Smaller table size

Applicati ication, on, Practices ctices and Enhanceme ncements nts Scramj amjets ts

High Speed Reacting Flows Densi nsity ty-bas based ed Solver er – 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

Advanced Initialization and Convergence Control Advanc nced ed Initi tializ lizat ation ion – Grid sequencing option – Fully implicit newton-type solution algorithm – Controllable number of coarse levels Continuity ntinuity Convergence ergence Accel elera erator or (CCA) A) – 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.

Supersonic Combustion • H 2 Fue ueled led NAS ASA A SCHOLA OLA direct ect-co connect nnect Scramj amjet t engine gine • Valida date agains nst t experime eriment nt and NAS ASA A VULCAN CAN code de Mesh: h: 1.4M Hex-dominant 10 Prism Layers Solver: er: Density based solver Steady,k-w SST, AUSM+FVS Non-adiabatic PPDF

Supersonic Combustion (2)