Description of twoPhaseEulerFoam Project in the course CFD with - - PowerPoint PPT Presentation

Introduction Case set-up Theory Post-processing

Description of twoPhaseEulerFoam Project in the course ’CFD with OpenSource Software’

Sandra Busch 2014-12-01

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Introduction Case set-up Theory Post-processing

Contents

Introduction Case set-up Theory Post-processing

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Introduction Case set-up Theory Post-processing

twoPhaseEulerFoam

Application twoPhaseEulerFoam Description Solver for a system of 2 compressible fluid phases with one phase dispersed, e.g. gas bubbles in a liquid including heat-transfer.

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Copy tutorial

Two tutorials available for the twoPhaseEulerFoam treating fluidized beds: laminar and RAS. Start by copying the directory in the run directory: cp -r $FOAM_TUTORIALS/multiphase/twoPhaseEulerFoam/ RAS/fluidisedBed $FOAM_RUN cd $FOAM_RUN/fluidisedBed

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Mesh

Adapt mesh to the new geometry and run BlockMesh

vertices ( (0 0 0) (0.28 0 0) (0.28 1 0) (0 1 0) (0 0 0.025) (0.28 0 0.025) (0.28 1 0.025) (0 1 0.025) ); blocks ( hex (0 1 2 3 4 5 6 7) (28 100 1) simpleGrading (1 1 1) );

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Definition of static bed height

Defined in system/setFieldsDict

defaultFieldValues ( volScalarFieldValue alpha.air 1 volScalarFieldValue alpha.particles 0 ); regions ( boxToCell { box ( 0 0 0 ) ( 0.28 0.4 0.025 ); fieldValues ( volScalarFieldValue alpha.air 0.60 volScalarFieldValue alpha.particles 0.40 ); } );

define static height of the bed default volume fraction of air αair = 1 solids volume fraction in bed αparticles = 0.4%

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Set fields

Before running setFields, 0/alpha.air.org and 0/alpha.particles.org have to be copied since they are backup files: cp 0/alpha.air.org 0/alpha.air cp 0/alpha.particles.org 0/alpha.particles Now setFields can be run from the case directory.

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Boundary conditions

The inlet velocity can be set in 0/U.air, the outlet will be defined as pressure outlet.

dimensions [0 1 -1 0 0 0 0]; internalField uniform (0 0.46 0); boundaryField { inlet { type interstitialInletVelocity; inletVelocity uniform (0 0.46 0); alpha alpha.air; value $internalField; } }

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Phase properties

Particle diameter defined in constant/phaseProperties

phases (particles air); particles { diameterModel constant; constantCoeffs { d 275e-6; } alphaMax 0.62; } blending { default { type none; continuousPhase air; } }

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Introduction Case set-up Theory Post-processing

Drag models

Drag model also defined in constant/phaseProperties

drag ( (particles in air) { type WenYu; residualAlpha 1e-6; residualRe 1e-3; swarmCorrection { type none; } } );

• ther models that can be set:

added mass heat transfer lift wall lubrication turbulent dispersion

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Drag models

Available drag models for twoPhaseEulerFoam:

Ergun Gibilaro GidaspowErgunWenYu GidaspowSchillerNaumann Lain SchillerNaumann SyamlalOBrien TomiyamaAnalytic TomiyamaCorrelated WenYu segregated

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Turbulence

Turbulence modelling can be set in constant/turbulenceProperties.air and constant/turbulenceProperties.particles .

RAS { RASModel kineticTheory; turbulence

• n;

printCoeffs

• n;

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Other properties

Define direction and value of the gravity in constant/g:

dimensions [0 1 -2 0 0 0 0]; value ( 0 -9.81 0 );

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ControlDict

application twoPhaseEulerFoam; startFrom startTime; startTime 0; stopAt endTime; endTime 2; deltaT 0.0002;

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Run solver

Run the solver : twoPhaseEulerFoam >& log &

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Multiphase solver

Some changes from earlier OpenFOAM versions: Phase property naming: alpha.<phase_name> denotes phase fraction of phase <phase_name> <property>.<phase name> denotes property <property> of phase <phase_name> Turbulence modeling for multiphase systems (different from single phase due to volume fraction) Different models for twoPhaseEulerFoam (drag, added mass, lift, heat transfer, turbulent dispersion and wall lubrication models)

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Multiphase equations (Eulerian-Eulerian)

Continuity equation

∂ ∂tαkρk + ∂ ∂xi αkρkUk,i = 0

Momentum equation

αkρk ∂ ∂tUk,i + Uk,j ∂ ∂xi Uk,i

• = αkρkgi − αk

∂Pl ∂xi − ∂τk,ij ∂xj + Ik,i

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Syamlal-O’Brien drag model

Drag force: FD = 1 2ρ2ACD|Vr|Vr

$FOAM_APP/solvers/multiphase/twoPhaseEulerFoam/ interfacialModels/dragModels/SyamlalOBrien

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Syamlal-O’Brien drag model

Foam::tmp<Foam::volScalarField> Foam::dragModels::SyamlalOBrien::CdRe() const { volScalarField alpha2(max(scalar(1) - pair_.dispersed(), residualAlpha_)); volScalarField A(pow(alpha2, 4.14)); volScalarField B ( neg(alpha2 - 0.85)*(0.8*pow(alpha2, 1.28)) + pos(alpha2 - 0.85)*(pow(alpha2, 2.65)) ); volScalarField Re(pair_.Re());

A = α4.14

2

B = 0.8α1.28

2

if α2 ≤ 0.85 B = α2.65

2

if α2 > 0.85

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Syamlal-O’Brien Drag model

volScalarField Vr ( 0.5 *( A - 0.06*Re + sqrt(sqr(0.06*Re) + 0.12*Re*(2.0*B - A) + sqr(A)) ) ); volScalarField CdsRe(sqr(0.63*sqrt(Re) + 4.8*sqrt(Vr))); return CdsRe *max(pair_.continuous(), residualAlpha_) /sqr(Vr); }

Vr = 0.5

• A − 0.06 Re +
• (0.06 Re)2 + 0.12 Re (2B − A) + A2
• CD

=  0.63 + 4.8

• Re

Vr

 

2

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paraFoam

The case can be opened in paraFoam: paraFoam

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paraFoam

Bed after 2.4 seconds of simulation showing symmetric behaviour:

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paraFoam

Bed after 20 sec of simulation time showing the volume fraction of the solids phase:

Syamlal-O’Brien Schiller-Naumann Wen-Yu Sandra Busch twoPhaseEulerFoam 2014-12-01 23 / 25

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paraFoam

Plot of the averaged volume fraction of the solids phase at different y-positions

Syamlal-O’Brien Schiller-Naumann Sandra Busch twoPhaseEulerFoam 2014-12-01 24 / 25

Introduction Case set-up Theory Post-processing

The end

Thank you for your attention!

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