Best Practices for Modeling Multi Phase Flows in Automotive Industry

Best Practices for Modeling Multiphase Flows in Automotive Industry

Tiberiu Barbat

June 10, 2004

Content

Introduction, Definitions and SpecificsMultiphase Models in FLUENT 6.1Ten Important Items for Multiphase Modeling with FLUENTBest Practices for using Multiphase Models in FLUENT 6.1 in Automotive Applications (I)

Transient VOF ModelSteady-State VOF Model

User PresentationBest Practices for using Multiphase Models in FLUENT 6.1 in Automotive Applications (I)

Mixture Multiphase ModelEulerian Multiphase ModelCavitation Model

FLUENT 6.2 - New Features for Modeling Multiphase FlowsConclusions

Introduction, Definitions and Specifics in Multiphase Flows

Phases = homogeneous parts of a heterogeneous system (Gas, Liquid, Solid)Phase boundaries = surfaces of discontinuity for macroscopic system properties (density, viscosity, etc.)

Shape and position of phase boundaries to be determined with the solution !Phase Interaction

Mass Transfer (Phase Change)Momentum Transfer (Drag, Lift, Virtual Mass)Surface TensionWall AdhesionHeat Transfer

gas phase=air+fuel vapors(two species)

interface gas-liquid

liquid phase (one species)

Introduction, Definitions and Specifics in Multiphase Flows

Phase Volume Fraction (α) = scalar field to capture phases distribution in Eulerian frameworkLarge number of CFD Multiphase models are solving transport equations for α

VVi

Vi δδα

δ 0lim

→≡

)()()(

cellVcellVcell i≡α 1=∑

iiα

δV2 δV

δV1

Alternatively, Lagrangian approach using Discrete Phase Model (DPM)Practical only if α < 10%

Multiphase Flow Regimes

Bubbly / Droplet / Particle-laden flow = Discrete secondary phase structures (bubbles, droplets, solid particles) in a continuous primary phaseSlug flow = Large bubbles in a continuous liquidAnnular flow = Continuous liquid along walls, gas in coreStratified / Free-surface flow = Immiscible fluids separated by a clearly-defined interfaceJet flow = thin liquid core surrounded by bulk gas phaseFilm flow = thin liquid layer flowing along wall boundaries

Bubbly flow / Droplet flow / Particle-laden flow

Slug flow

Annular flow

Jet flowFilm flow

Free-surface flow

Multiphase Models in FLUENT 6.1

Volume-of-Fluid (VOF) ModelFree surface / stratified flows; annular and slug flows; jet and film flowsMesh is resolving all primary and secondary phases flow fieldPhase interfaces are captured in the limit of the mesh resolutionOne set of continuity, momentum and energy equations (α-averaged)Transport for secondary phase(s) volume fractionSeveral formulations available – differ through the method of solving for α


Mixture Multiphase ModelBubbly / droplet / particle-laden flows with small particle relaxation timeInterpenetrating phases; phase boundaries are not resolvedMesh is resolving flow field of a “mixture” fluid, α-averaged local propertiesSecondary phases form structures (bubbles, droplets, solid particles) which are not resolved by the mesh; their size is input for the drag forcesModel Phase Interaction through constitutive equation for slip velocity and drag forces between phasesOne set of momentum and energy equations


Eulerian Multiphase ModelBubbly / droplet / particle-laden flows; granular physics option for solid phasesInterpenetrating phases; phase boundaries are not capturedMesh is resolving phase average flow and energy fields for all primary and secondary phasesSecondary phases form structures (bubbles / droplets / particles – granules) not resolved by the mesh; size of the structures are input for drag / virtual mass / lift / collisional forces on the particlesMomentum and energy equations for each phase


Cavitation ModelPhase change when local pressure becomes lower than vaporizationpressure; mechanical work is main cause, no significant heat transferFLUENT 6.1 introduced a new cavitation model, more robust and with more physics includedPrimary phase – the liquidSecondary phase – the vapor and a specified amount of non-condensable gas


Cavitation ModelPhase change captured in both directions (cavitation and condensation) through model for mass transfer rate between phases included in vapor phase volume fraction transport equationPhase boundary - is not resolvedWas implemented within the frame of the Mixture Multiphase model

one set of momentum and energy equations; bubble size input refers to drag forces onlyhomogeneous or flow with slip between the phases

Variable density allowed for phases

Ten Important Items for Multiphase Modeling with FLUENT

1. Analyze physical problem for Multiphase flow regime(s) and driving forces2. Identify the appropriate Multiphase model(s) available in FLUENT3. Establish any need for customization and additional models through UDF’s4. Formulate specific meshing requirements for Multiphase problems5. Choose Model options and specific settings6. Identify the right numerical procedures and solver settings7. Set the time step for efficient and stable runs in transient Multiphase problems8. Input appropriate Boundary Conditions for the Multiphase problem9. Input Initial Conditions for the Multiphase simulation10. Identify variables, images, and other appropriate information to be monitored and

saved during the run for testing convergence and postprocessing

Best Practices for using VOF Model for Transient Problems

1. Analyze physical problem for Multiphase flow regime(s) and driving forces

Free Surface FlowFilling Problems – Gravity and Inlet flow

Fuel TankTransmission Fluid

Drainage Problems - GravityRain water management in HVAC system cowlCondensation water from air-side of the evaporator

Sloshing Problems – Gravity and InertiaFuel TankOil PanPower Steering Reservoir

Jet & Film Flow – Gravity, Inlet Flow and InertiaCooling and Lubrification

Piston HeadFuel injector

Annular Flow / Slug Flow – Inlet Flow and GravityTwo-Phase Heat Exchangers - Evaporator


2. Identify the appropriate Multiphase model(s) available in FLUENTVolume-of-Fluid (VOF) – 4 formulations available grouped in two categories based on how the fluxes are computed in the Volume Fraction (α) equation

(a) Solve α equation with Interface ReconstructionGeo-Reconstruct VOF

Explicit time marching solution for αMost accurate for shape of the interface (linear slope)

Donor-Acceptor VOFExplicit time marching solution for αLess accurate for interface shapeAble to handle highly skewed cellsWorks only on quad / hexa mesh

(b) Solve α equation as any other transport equationEuler Explicit VOF

Explicit time marching solution for αInterface is diffused, not sharp; needs high order discretizationLast resort solution

Implicit VOFImplicit solution for αAllows larger time stepsDiffused interface, needs high order discretization


Implicit with 2nd order upwind Geo-Reconstruct

Donor - Acceptor

With Interface ReconstructionRegular Discretization Methods,No Interface Reconstruction


3. Establish any need for customization and additional models through UDF’s(a) Phase Change

Fuel Tank FillingEvaporation – Compute and Prescribe Evaporation RateSpecies Diffusion – through User Defined Scalars (UDS)

Two-Phase Flow in EvaporatorsBoiling / Condensation – Compute and Prescribe Mass Transfer Rate

(b) Boundary ConditionsHydrostatic Pressure at Pressure Inlets and Outlets

(c) Initial ConditionsInterface shape and flow field at t=0

(d) PostprocessingInterface shape and center of gravityMass / Volume of liquid / gas in the domain


4. Formulate specific meshing requirements for Multiphase problemsFree surface details are captured in the limit of mesh resolution

Phase boundaries are not postprocessed directly - only the volume fraction field values determine the interface shape and locationDroplets / bubbles smaller than mesh size will not be correctly described by the volume fraction solutionAt least 4 - 9 cells are required to capture a droplet / bubble through values of volume fraction field


4. Formulate specific meshing requirements for Multiphase problemsDonor-Acceptor VOF is available ONLY for Quad / Hexa meshGeo-Reconstruct VOF works with any type of mesh (tri / quad / tet / hex / hybrid), but keep in mind that

General requirements (cell skewness, size change, aspect ratio) for FLUENT meshes should be strictly enforced

Maximum cell skewness 0.95Maximum aspect ratio 5Smooth size change between adjacent cells

Time step size for the explicit α equation is internally determined by the solver on interface cells; if interface is passing quickly through regions with unnecessary fine mesh, the required time step for stable runs will be very small (See Item 7 – Set the time step ..)


5. Formulate specific meshing requirements for Multiphase problemsIf Geo-Reconstruct VOF or Donor-Acceptor VOF are used, slit all the double-sided wall boundaries before running the simulation (TUI command)

/grid/modify-zones/slit-face-zoneIf Surface Tension or Wall Adhesion Phase Interaction effects are to be captured

Use Quad / Hexa meshesMesh should be generated as uniform and isotropic as possible

DO NOT use Hexcore meshes for VOF Cases in FLUENT 6.1

Slit Baffles (Double-sided walls) when using Geo-Reconstruct VOF !


5. Choose Model options and specific settingsImplicit Body Force formulation

Should be turned ON for all transient VOF problems in Automotiveapplications driven by Gravity and Inertia Forces

Solve VOF Every IterationShould be kept OFF (Default)

Courant NumberShould be kept at 0.25 (Default)

Operating ConditionsGravity componentsSpecified Operating Density

Should be turned ONSpecify the density of the lighter phase

Reference Pressure LocationSpecify a location where the lighter phase is found


6. Identify the right numerical procedures and solver settingsGradient Option in Define>Models>Solver

Node-Based is preferredPressure Discretization schemes: ONLY

PRESTO!Body Force Weighted

Pressure-Velocity CouplingPISO

Skewness Correction decreased to 0Neighbor Correction kept to 1Skewness-Neighbor Coupling turned ON


7. Set the time step for efficient and stable runs in transient Multiphase problemsTwo time scales in the transient VOF problems using Interface Reconstruction

Physical time step (user specified) ∆tVOF sub-time step (internally computed by FLUENT) ∆τ

Momentum, turbulence, energy, and other scalar equations are solved with the ∆tspecified by the user in Solve>IterateVolume fraction α equation is solved explicitely with ∆τ Simulation is stable and efficient when

VOF sub-time step Varies during the simulation Represents minimum time to move secondary phase(s) out of an interface cell at that instantDepends on

Mesh resolution in the interface cellsFluxes in the interface cellsCourant number user input (default 0.25)

2010K≤∆∆τt


7. Set the time step for efficient and stable runs in transient Multiphase problemsHow to find out ∆τ in order to determine a good ∆t ?

FLUENT has this information computed at each time stepSolution 871 on www.fluentusers.com explains in detail the following procedureStart the simulation with a small time step ∆t1 allowing good convergence within 20 iterations per time stepRun a number of time steps to get the flow goingSave converged data fileSpecify a very large time step ∆T (at least 6 orders of magnitude larger than originally)FLUENT will pass an error message detailing the number (N) of VOF sub-time steps needed to cover the specified ∆T Now the VOF sub-time step can be computed simply as

Now user can continue the simulation with a physical time step ∆t2 within the limit of 10-20 VOF sub-time steps

NT∆

=∆τ


8. Input appropriate Boundary Conditions for the Multiphase problemSpecify volume fraction for secondary phases at velocity-inlet and pressure-inlet boundariesSpecify realistic backflow volume fraction for secondary phases at pressure-outlet boundaries depending on gravity direction and boundary orientationSpecify mass flow rates for each phase at mass-flow-inlet boundariesDo not use outflow boundaries in transient VOF cases

g

ωV / p

p

ax


9. Input Initial Conditions for the Multiphase simulationPatch volume fraction for secondary phase(s) to match initial phase distribution in the problem

On predefined cell zonesBetter interface control

On registers of cells created with Adapt menu toolsMore versatile, suitable for parametric studies

Use custom field variables Use UDF for initialization


10. Identify variables, images, and other appropriate information to be monitored and saved during the run for testing convergence and postprocessing

Free surface flows with bulk phasesDefine free surface through an Iso-Surface of constant volume fraction of 0.5 (named for example “vf05”) created from the entire domain

Surface>Iso-Surface>Phases>Volume Fraction of the phase of interest, no surface picked in the selection list

“vf05”


Create a surface for all fluid zonesSurface>Zone, create surfaces for each fluid zoneSurface>Manage, group these surfaces in “fluid-all”

Define the areas of the boundary zones wetted by the phase of interest through an Iso-Clip surface of volume fraction between 0.5 and 1 (named for example “clipf”, clipped out of all fluid zones

Surface>Iso-Clip>Phases>Volume Fraction, select “fluid-all”Display>Grid only Faces on the “vf05” and “clipf”, color them differently in Display>Scene

“clipf”


•Display>Grid only Faces on the “vf05” and “clipf”


•Use these surfaces for transient interface shape, by simply re-displaying them with the new data



Jet / Film FlowsThe postprocessing is more delicate, one of the phases (say the liquid for example) occupies a much smaller / narrow group of cells in the domain than the bulk phase (gas)Using the previous method from Free Surface Flows may lead to wrong conclusions about the extent and continuity of the liquid jet or film

Cells with volume fraction less than 0.5 would not be includedUse instead Velocity Vectors colored by the phase of interest, between a specified range of 0.01 and 1, to capture the direction of the flow and extent of the liquid jet / film

Display>Velocity Vectors>Colored by Phase>Volume Fraction, Clip to Range 0.01-1

Use Contours of Volume Fraction on sections through the model



Velocity Vectors colored by the phase of interest, between a specified range of 0.01 and 1

Best Practices for using Implicit VOF for Steady State Solutions

1. Analyze physical problem for Multiphase flow regime(s)Jet Flow – Fuel InjectorFlow driven by high pressure at the fuel inlet

2. Identify the appropriate Multiphase model(s) available in FLUENTTwo phases – liquid fuel and gaseous air – clearly separatedInterface shape is of importance – determine cone angleVOF Model for the portion of the domain up to the liquid sheet breakupSeparate inflows for the two phases – liquid fuel and airSteady state implicit VOF can be used if no transient boundary conditions and initial jet development stage is not of interestTransient Geo-Reconstruct is expensive and not needed

3. Establish any need for customization and additional models through UDF’s


4. Formulate specific meshing requirements for Multiphase problemsCan use either hexa / hybrid / tetra mesh (hexa preferred)Good mesh resolution in the area of the jet / liquid sheet

5. Choose Model options and specific settingsImplicit Body Force formulation ON

6. Identify the right numerical procedures and solver settingsPressure Discretization – Only these two schemes should be used

Body Force WeightedPRESTO!

Momentum, Turbulence, Volume Fraction DiscretizationQUICK on Hexahedral MeshesSecond Order on Hybrid / Tetra meshes

Under-Relaxation FactorsPressure 0.2 - 0.3Momentum 0.5 –0.7Volume Fraction 0.2 –0.5

7. Set the time step for efficient and stable runs in transient Multiphase problems


8. Input appropriate Boundary Conditions for the Multiphase problemUse a domain large enough to minimize reversed flow areasSpecify backflow volume fraction 0 for liquid

9. Input Initial Conditions for the Multiphase simulationSolve first without Volume Fraction equation, then solve all equations


Identify the interface shape – cone angleVolume Fraction contour plots on sectionsVelocity Vectors colored by Volume Fraction of liquid within 0.01-1 range


Velocity Vectors colored by the phase of interest, between a specified range of 0.01 and 1


Best Practices for using Mixture Model

1. Analyze physical problem for Multiphase flow regime(s) and driving forcesPhase Separation Problems

Droplet Flow - Inertia (centrifugal) forces and GravityOil Separator for Automotive HVAC

2. Identify the appropriate Multiphase model(s) available in FLUENTEstimate average Volume Fraction of secondary phaseIf below 10%, consider using DPMCompute time scale characteristic for primary phase flow TAssume a diameter for secondary phase structures dCompute relaxation time for secondary phase structures tCompute Stokes number St =t/TMixture Model is applicable if St <<1

3. Establish any need for customization and additional models through UDF’sDrag customizationDroplet diameter distributionInitialization

4. Formulate specific meshing requirements for Multiphase problemsAny mesh type (hexa, tetra, hybrid) of good qualityNo need for boundary layers here


5. Choose Model options and specific settingsSlip Velocity ONImplicit Body Force formulation ONTurbulence Model

RNG k-e with Swirl Flow optionRSM

6. Identify the right numerical procedures and solver settingsPressure discretization

Body Force WeightedPRESTO!

First Order for starting the problem, Second Order for accurate solution for rest of equationsSolve in steps

Flow and Turbulence (primary phase flow)Flow, Turbulence and Volume Fraction (homogeneous multiphase flow)Flow, Turbulence, Volume Fraction and Slip Velocity (multiphase with slip)

7. Set the time step for efficient and stable runs in transient Multiphase problemsLower Under-Relaxation Factors than Defaults

Pressure 0.1-0.3Turbulence 0.2-0.4Volume Fraction 0.1-0.5Slip Velocity 0.001-0.1

Run the problem as transient to steady-state


8. Input appropriate Boundary Conditions for the Multiphase problemVelocity field can be different at velocity inletsBackflow value for volume fraction of secondary phase to be realistic

9. Input Initial Conditions for the Multiphase simulationUse Solve>Patch to patch volume fraction fields which are closer to solution


Volume Fraction fieldsMass flow rates per phasePressure fieldSlip velocity

Best Practices for using Eulerian Multiphase Model

1. Analyze physical problem for Multiphase flow regime(s)

Oil separator in HVAC systemDroplet flowDriving forces – inlet flow, inertia (centrifugal) and gravity

2. Identify the appropriate Multiphase model(s) available in FLUENT

Droplet sizes are largeParticle relaxation time is large relative to characteristic time scale of flowStokes number St >1

3. Establish any need for customization and additional models through UDF’s

Drag customizationsDroplet diameter distributionInitialization

4. Formulate specific meshing requirements for Multiphase problems

Any mesh type (hexa / tetra / hybrid) of good quality; hexa mesh preferredBoundary layers elements to capture flow separation


5. Choose Model options and specific settingsImplicit Body Force formulation ONMultiphase turbulence option

Dispersed to start with (more robust)Per-phase for final solution

Virtual Mass OFFLift Forces OFFDrag model – Schiller & NaumannInterphase Heat Transfer – Ranz-Marshall correlation

6. Identify the right numerical procedures and solver settingsSolve in steps

Flow and Turbulence (primary phase flow)Flow, Turbulence and Volume Fraction (multiphase flow)

Adjust properties of second phases in stepsStart with similar properties for all phasesAdjust density and viscosity of secondary phases to real values in steps

Adjust boundary conditions for volume fraction in steps


7. Set the time step for efficient and stable runs in transient Multiphase problemsUse lower URF’s than regular

Pressure 0.1-0.3Turbulence 0.1-0.4Volume Fraction 0.1-0.5

Run the problem as transient to steady-state8. Input appropriate Boundary Conditions for the Multiphase problem

Pressure value is the only common inputTemperature per phaseTurbulence per-phase requires turbulence boundary conditions for each phase

9. Input Initial Conditions for the Multiphase simulationUse a Mixture model solution for a modified problem (St<<1) to initialize the problemUse Patch with custom field functions and UDF’s


Best Practices for using Cavitation Model

1. Analyze physical problem for Multiphase flow regime(s)Liquid fuel under high pressure differences in a fuel injectorDriving forces – pressure gradient and phase changeVapor phase develops in regions of high velocity, where p<pvaporization

2. Identify the appropriate Multiphase model(s) available in FLUENTCavitation Model – within framework of Mixture Model in FLUENT 6.1

3. Establish any need for customization and additional models through UDF’sDrag customization

4. Formulate specific meshing requirements for Multiphase problemsHexa mesh is preferred

Dynamic Mesh and Cavitation only hexa meshFine mesh in cavitating areas


5. Choose Model options and specific settingsMixture Model

Liquid primary phaseVapor secondary phase

Mass Transfer – Cavitation ONLiquid properties

Vaporization pressureSurface Tension

Mass Fraction of Non-Condensable gas (e.g., air)Constant (no de-gassing effects)Non-zero, stabilizing numerical effect

Slip Velocity OFFImplicit Body Force formulation OFF

6. Identify the right numerical procedures and solver settingsPressure Discretization

Body Force WeightedPRESTO

Momentum, Turbulence, and Volume FractionSecond OrderQUICK

Reduce the pressure-correction under-relaxation (hidden URF, default is 0.7)Scheme command (rpsetvar ‘pressure-correction/relax 0.4)Do not reduce it below 0.4


7. Set the time step for efficient and stable runs in transient Multiphase problemsVery low URF’s relative to Default, except Pressure

Pressure 0.4-0.6Momentum 0.1-0.3Volume Fraction 0.1-0.5Vaporization Mass 1e-6 – 0.1

8. Input appropriate Boundary Conditions for the Multiphase problem9. Input Initial Conditions for the Multiphase simulation

Obtain initial condition as solution of a modified (milder) problemStart with high pressure at pressure-outlet, no cavitationDecrease back-pressure to initiate cavitation and adjust it in stepsAdjust vaporization pressure in steps



Vapor phase volume fraction includes the amount of non-condensable gas

New Features in FLUENT 6.2 useful for Multiphase Modeling

1. VOF ModelSpeed Improvements

Optimized Iterative PISO Pressure-VelocitySpeed Increase by a factor of 2 versus FLUENT 6.1

Non-Iterative Time Advancement (NITA)New Transient algorithms with one iteration per time stepVery efficient compared with Iterative PISOGood accuracy compared with Iterative PISO as benchmarkSpeed Increase by a factor of 9 versus FLUENT 6.1

Variable Time Stepping for VOFUser specified controls

New Features in FLUENT 6.2 useful for Multiphase Modeling1. Transient VOF Geo-Reconstruct for Tank Sloshing with Non-Iterative Time Advancing

(NITA) Algorithms

FLUENT 6.1PISO CPU=29,591

FLUENT 6.2ITERATIVE PISO CPU=15,794

FLUENT 6.2NITA –Fractional Step CPU=4,043

FLUENT 6.2NITA – PISO CPU=3,450


1. VOF ModelSpeed Improvements

Modified High Resolution Interface Capture (HRIC)Better resolution than QUICK or Second Order, but more diffuse than Geo-ReconstructVery efficient for Steady-State and Transient problems where getting faster to final interface shape is more important than accurate interface shape historySpeed Increase by a factor of 100 versus Geo-Reconstruct

Fuel InjectorHydroplaningSealing Problems


Swirl Fuel Injector FLUENT6.1 First Order


Swirl Fuel Injector FLUENT6.1 Second Order


Swirl Fuel Injector FLUENT 6.2 Modified High Resolution Interface Capture (HRIC)


1. VOF ModelNew Physics

Species Transport and Chemical ReactionsMass Transfer across phase boundaries must be specified through UDFEvaporation at Free Surface

Inviscid FlowsShip Hydrodynamics

New Boundary ConditionsOpen Channel Boundary Condition

Mitigate the reflection of free surface waves at flow boundariesSurface Tension Force implementation has improved

Larger time steps allowedFaster convergence


2. Mixture ModelNew Physics

Granular option for solid phase particle-particle interactionSpecies Transport and Chemical Reactions

Mass Transfer Rate across phase boundaries specified through UDFNucleate Boiling

3. Eulerian Multiphase ModelNew Physics

Species Transport and Chemical ReactionsMass Transfer Rate across phase boundaries specified through UDF

Nucleate BoilingRSM Turbulence model for dilute Eulerian Multiphase Flows

Mixture-basedVery dilute flowsPhases have similar properties

Dispersed-basedDilute flows

Additional granular optionsPDE for granular temperature


2. Cavitation ModelLiquid and vapor phase compressibilityVaporization pressure can be specified as a function of temperatureEnhanced robustness and speed

Less sensitivity to initial conditions and under-relaxationFuel injectors with large pressure differencesRotating machinery

Water pumpsBearings

Conclusions

Multiphase Flow and Heat Transfer Problems require several different Multiphase Models in order to deal with different situations

Multiphase Flow RegimesTransient or Steady State Flow Dilute or Dense FlowsNeed for accurate capture of free surface shape

FLUENT6.1 has Multiphase Models able to tackle all the Multiphase Flow Regimes and problems encountered in Automotive Industry applications

Volume-of-Fluid (VOF)Geo-Reconstruct for accurate shape, transient problemsImplicit for steady-state problems and transient with larger time-steps

Mixture ModelBubbly / Droplet flow with small relaxation time (small droplets)

Eulerian ModelBubbly / Droplet flowGranular options

Cavitation ModelMixture Model approach to phase change in areas with pressure lower than the vaporization pressure of a liquid

All Multiphase Models in FLUENT6.1 allow for Heat Transfer computationsPhase Change modeling requires in general UDF implementation (except Cavitation)

Conclusions

Running a Multiphase Flow & Heat Transfer Problem in FLUENT6.1 requires the userBe proactive in mesh quality and resolution issues

Skewness and aspect ratio limitsTime step and grid resolution are linked for Geo-Reconstruct explicit VOF formulation

Change some settings for numerical discretization and other specific inputsUse only Body Force Weighted or PRESTO Pressure discretizationPISO pressure-velocity coupling for transientUnder-relaxation factors schedules

Patch initial conditions or start from a solution of a modified problemSelect equations in steps

FLUENT 6.2 brings in new features and improvements to all Multiphase ModelsSpecies and Chemical Reactions with all Multiphase ModelsTransient efficiency improvements for VOF – Non-Iterative Time Advancement algorithms (NITA)Variable Time Stepping for Transient VOFNew method of capturing the interface with implicit VOF – High Resolution Interface Capture (HRIC) schemeMore physics in Mixture Model (granular option)More physics in Cavitation Model

Vaporization pressure varies with temperatureLiquid and vapor phase compressibility

Documents

Best Practices for Modeling Multi Phase Flows in Automotive Industry