Numerical prediction of the flow around a marine...

IntroductionPropeller in Uniform Flow

Cavitation ModellingConclusions

Numerical prediction of the flow around amarine propeller

Mitja Morgut

Department of Naval Architecture,Ocean and Environmental Engineering, DINMA

University of TriesteTrieste, Italy

September 14, 2009

NUMAP-FOAM 2009 Zagreb, 14 September



Outline

1 IntroductionRoad Map

2 Propeller in Uniform FlowNumerical MethodComputational DomainsResultssimpleSRFFoam

3 Cavitation ModellingMyRASinterPhaseChangeFoamFull Cavitation Model

4 Conclusions




Road Map

Introduction




Road Map

Road Map




Numerical MethodComputational DomainsResultssimpleSRFFoam

Propeller in Uniform Flow





Numerical Method

The developed CFD procedure:

considers only one passage bladeemploys a MFR (Multiple Frame of Reference) approachmeshes are generated using ANSYS ICEM CFD 11calculations are performed with MRFSimpleFOAMturbulence is modelled using SpalartAllmaras model





Computational DomainsIn this case simulations were performed using two different computational domains:

DOMAIN ARotating Fixed

Hmid 0.17DLmid 0.76D

L1 1.5DL2 5DH2 1.38D

DOMAIN BRotating Fixed

Hmid 0.17DLmid 0.76D

L1 1.5DL2 5DH2 4.3D

D = Diameter of the Propeller

Lmid = Length of part Rotating





Propeller E779a

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.5

1.0

J

KT

, 10K

Q

KT

10KQ

Exp. DataMRF Domain AMRF Domain B

ε(KT )% =KT ,NUM−KT ,EXP

KT ,EXP· 100

ε(KQ )% =KQ,NUM−KQ,EXP

KQ,EXP· 100

Domain A Domain BJ εKT (%) εKQ (%) εKT (%) ε(KQ )(%)

0.249 14.30 10.82 -4.95 -1.410.498 13.40 10.33 -3.87 1.210.596 12.00 7.46 -3.12 1.350.695 13.12 5.45 -3.71 1.760.845 4.55 -3.90 4.55 1.260.946 -4.67 -10.93 -9.96 2.14

The INSEAN E779A Propeller Dataset,INSEAN Propulsion and Cavitation Laboratory, 2006





SimpleSRFFoam

Simulation on Domain A

Suction Side Pressure Side

Comment: Pressure distribution completely wrong. (J=0.695)

Simulation on Domain BUnder Investigation




MyRASinterPhaseChangeFoamFull Cavitation Model

Cavitation Modelling





MyRASinterPhaseChangeFoamIn momentum equation, subgrid viscosity (µS) replaced by turbulent viscosity (µt )

interPhaseChangeFoam MyRASinterPhaseChangeFoam

surfaceScalarField muf =twoPhaseProperties->muf()+ fvc::interpolate(rho*turbulence->nuSgs());

surfaceScalarField muEff =(muEff,twoPhaseProperties->muf()+ fvc::interpolate(rho*turbulence->nut()));

fvVectorMatrix UEqn(fvm::ddt(rho, U)+ fvm::div(rhoPhi, U)- fvm::Sp(fvc::ddt(rho) + fvc::div(rhoPhi), U)- fvm::laplacian(muf, U)- (fvc::grad(U) & fvc::grad(muf)));

fvVectorMatrix UEqn(fvm::ddt(rho, U)+ fvm::div(rhoPhi, U)- fvm::Sp(fvc::ddt(rho) + fvc::div(rhoPhi), U)- fvm::laplacian(muEff, U)- (fvc::grad(U) & fvc::grad(muEff)));





Full Cavitation Model, TheoryThe momentum conservation equation for the mixture is:

∂

∂t(ρm−→v m) +∇ · (ρm

−→vm−→v m) = −∇p +∇ · [µm(∇−→v m +∇−→v T

m)] + ρm−→g +

−→F (1)

The mass conservation equation for the mixture

∂

∂t(ρm) +∇ · (ρm

−→v m) = 0 (2)

The ρm − fv (Mixture density - vapour mass fraction) relationship

1ρm

=fvρv

+1− fvρl

(3)

The vapour phase (αv ) volume fraction

αv = fvρm

ρv= 0 (4)





Full Cavitation Model, Theory

The trasport equation for the vapour mass fraction fv

∂

∂t(ρmfv ) +∇ · (ρm

−→v mfv ) = ∇ · (Γ∇fv ) + Re − Rc (5)

The source terms:8>>><>>>:Re = Ce

Vchγρlρv

q23

pv−pρl

(1− fv ), when p < pv

Rc = CcVchγρlρl

q23

p−pvρl

fv ,when p > pv(6)

Vch =√

k , Ce = 0.02, Cc = 0.01 (7)

Singhal, A.K., et. al., 2002, Mathematical Basis and Validation of the Full CavitationModel, J. Fluids Eng., 124, pp. 617-623





Full Cavitation Model, Implementation, MyFCM

In the solver interFoam, the GammaEqn.H was replaced by the trasport equation forthe vapour mass fraction, (Eqn. (2)). The mixture density is computed using Eqn. (3).

fvScalarMatrix fEqn(fvm::ddt(rho, f)+ fvm::div(rhoPhi, f)- fvm::laplacian(muEff, f)+ fvm::Sp(SpCoeff,f)- ScCoeff

);

solve(

fEqn);

rho=scalar(1)/((f/rho2)+((1-f)/rho1));rhoPhi=phi*fvc::interpolate(rho);





Venturi Type Section

Ventury-type section1

σ = 2.4,

Vref = 7.2m/s

MyRASinterPhaseChangeFoam

MyFCM

[1] Coutier-Delgosha, O., et. al, 2003, Evaluation of the Turbulence Model Influence on the Numerical Simulations of

Unsteady Cavitation, J. Fluids Eng., 125, pp. 38-45





Naca 0015

Contours of the Vapour Volume Fraction

MyRASinterPhaseChangeFoam MyFCM

Vin = 6m/sα = 8o

Re = 3 · 105

σ = 1.2




Conclusions




Conclusions

What I have achieved:Procedure for the prediction of the flow around a marine propeller working in

uniform flow and non cavitating conditions

What I am planning to do:Investigate the influence of the turbulent model on the prediction of theperformances of the propeller working in uniform flow

Validate the cavitating flow solver MyRASinterPhaseChangeFoam

Improve the cavitating flow solver MyFCM

Develop a procedure for the prediction of the flow around a marine propeller

working in uniform flow and cavitating conditions


Numerical prediction of the flow around a marine...

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