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Draft Tube calculations using OpenFOAM-1.5dev and validation with FLINDT data

C. Devals, Y. Zhang and F.GuibaultÉcole Polytechnique de Montréal, Canada

T. Vu and B. NennemannAndritz Hydro, Pointe-Claire, Canada

6th OpenFOAM Workshop, June 13-16 2011, PennState University, USA

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Viscous flow simulations for hydraulic turbo-machinery design

Runner

Draft-tube

Spiral

casing

Context

Distributor

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� Previous work:� 25th IAHR Symposium on Hydraulic Machinery and Systems

September 20-24, 2010, Timisoara, Romania� Steady and unsteady flow computation in an elbow draft tube with

experimental validationT.C. Vu, C. Devals, Y. Zhang, B. Nennemann and F. GuibaultInternational Journal of Fluid Machinery and SystemsVol 4, No 1, January-March 2011

Context

Lt=0.5%DthLt=1%Dth Lt=0.25%Dth

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� Understand why the recovery coefficient for Phi=0.368 shows an important decrease for Lt=0.5%Dth.

� Validate OpenFOAM RANS simulations for draft tube on hexahedral meshes

� Compare recovery coefficient χ prediction with experimental data

Objectives

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Model draft tube test: FLINDT� FLINDT is for FLow INvestigation in Draft Tubes Project (LMH-EPFL Switzerland)� Throat diameter: Dth = 0.4 m� Rotational speed: N=1000 RPM

� Angular velocity: ϖ=104.66 Hz

� Flow coefficient ϕ: 0.340, 0.360, 0.368, 0.380, 0.390 and 0.410

� corresponding swirl: 0.332, 0.242, 0.214, 0.198, 0.149 and 0.076

� Recovery coefficient

�∆pstat static pressure difference between inlet and outlet

� Aref reference section area Aref=0.17538m2

Test Case Description

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thR

Q

πϖϕ =

2

2

1

∆=

ref

stat

A

Q

P

ρ

χ

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� Steady state Reynolds averaged Navier-Stokes equations

�Newtonian fluid

� turbulence model

126

1

10.89257.0

kg.m997

−−

−

==

=

smlamρ

µν

ρ

ε−k

turblam

T

U

UUIp

UU

ννν

νρ

+=

=⋅∇

∇+∇+−⋅∇=⊗⋅∇

0

))(()(

r

rrrr

Physical Properties and Models

ρε

ρ

µν

2kCmu

turbturb ==

lam

turbrel

µ

µµ =

7

Boundary Conditions

Inlet

pressure

type zeroGradient

U, k

type profile1DfixedValue

fileName "profil-rr.csv"

epsilon

type turbulentMixingLengthDissipationRateInlet

mixingLength 0.0003285

U profile k profile

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Boundary Conditions

Outlet

pressure

type fixedMeanValue

meanValue 0

value uniform 0

U, k and epsilon

type zeroGradient

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Boundary Conditions

pier

U

type fixedValue

value uniform (0 0 0)

p, k and epsilon

type zeroGradient

No slip Wall condition

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Boundary Conditions

main

U

type fixedValue

value uniform (0 0 0)

p, k and epsilon

type zeroGradient

No slip Wall condition

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Boundary Conditions

ext

U

type fixedValue

value uniform (0 0 0)

p, k and epsilon

type zeroGradient

No slip Wall condition

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� Steady state (RANS) calculations (10000 iterations)� Solver: SimpleFOAM� Convection term discretization: normalized variable diagram (NVD)

scheme GammaV (between 0 and 1)� Linear solver: PBiCG for all variables except P,

GAMG for P� Turbulence model: k-epsilon� Velocity inlet BC : axi-symmetrically averaged velocity measures� Turbulence inlet BC: axi-symmetrically averaged k measures

4 turbulence length scales tested (epsilon)� Convergence: tolerance of 1.e-6, relTol of 0.01 for all variables

� Monitoring variable: pressure recovery factor

Numerical Model

2

2

1

∆=

ref

stat

A

Q

P

ρ

χ

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�Mesh investigation

�Scheme GammaV investigation: ψ=0, ψ=0.5 and ψ=1GammaV is the improved version of the NVD gamma scheme(ψ=0 best accuracy and ψ=1 more robust)

�Mixing length investigation: Lt=0.25%Dth, 0.5%Dth, 1.0%Dth and 5%Dth

�Initial conditions investigation

Test Cases

# nodes # elements

CRS 288744 276560

STD 782283 757968

FINE 1875470 1830884

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�Mesh investigation

�Scheme GammaV investigation

�Mixing length investigation

�Initial conditions investigation

Test Cases

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Mesh investigation – GammaV 1

Standard mesh Fine meshCoarse mesh

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Mesh investigation – GammaV 1

Standard meshCoarse mesh Fine mesh

Phi=0.368

X=-0.25

Phi=0.380

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Mesh investigation – GammaV 1 – Phi=0.380

Static Pressure

AxialComponent

RadialComponent

Energy

TangentialComponent

CFDExperimental Data

Steady probe CFDExperimental Data

Steady probe

Fine meshCoarse mesh

202

207203

205

209

208

213

211 214

ct2ct1

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�Mesh investigation

�Scheme GammaV investigation

�Mixing length investigation

�Initial conditions investigation

Test Cases

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GAMMAV 0.5 GAMMAV 1.0GAMMAV 0.0

Scheme investigation – GammaV – Coarse mesh

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�Mesh investigation

�Scheme GammaV investigation

�Mixing length investigation

�Initial conditions investigation

Test Cases

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Mixing length investigation – Standard mesh – GammaV 1

Lt=0.25%Dth Lt=0.50%Dth Lt=1.00%Dth Lt=5.00%Dth

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Relative Viscosity – Lt=0.50%Dth Relative Viscosity – Lt=5.00%Dth

X=0.25

X=-0.20

X=-0.25

X=0.20

X=0.25

X=-0.20

X=-0.25

X=0.20

X=0.00 X=0.00

Mixing length investigation – Standard mesh – GammaV 1

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�Mesh investigation

�Scheme GammaV investigation

�Mixing length investigation

�Initial conditions investigation

Test Cases

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Initial condition investigation – Std mesh – GammaV 1 – Lt=0.25%Dth

Initial conditions

from no previous calculation

Initial conditions

from previous calculation

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Conclusions

� Results are quite good compared to experimental data� Results are not so sensitive to mesh resolution except for Phi=0.368� Results are sensitive to scheme� Results are sensitive to initialization

Perspectives

� Validation and comparison with OpenFOAM-1.6ext� Runner and Draft-Tube calculations� Unsteady cases� Wall function investigation

Conclusions and Perspectives

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Thank you for your listening

Any questions?