Numerical investigation of the swirling flow and the...

University of Stuttgart

Institute of Fluid Mechanics and Hydraulic Machinery

Numerical investigation of the swirling flow

and the vortex control in a straight diffuser

Ivana Buntic-Ogor

Timo Krappel

Oliver Kirschner

Albert Ruprecht



Buntic-Ogor I. et al., Numerical investigation of the swirling flow and the vortex control in a straight diffuser

5th OpenFOAM Workshop, Chalmers University of Technology, 21-24.06.2010



• Introduction / Motivation

• Test rig and swirl generator

• Available measurements

• Numerical setup

• Numerical results and comparison

• Conclusion

Contents





Introduction / Motivation

• In hydro power industrial praxis swirling flow appears mostly in the

Francis turbines as a consequence of the part or over load

operation

• Appearance of the vortex rope

• High power losses

• Vortex rope causes strong pressure

pulsations which can lead to resonance

• Prediction of vortex rope of the industrial importance





Test rig





Swirl generator

80 mm

130 mm

2 x 8,6°





Swirl generator and straight cone





Available measurements

• Numerous measurements for different operational points have been

carried out. Varied were:

• blade angle (15°-30° opening)

• total discharge (30-45 m3/h)

• discharge of axial jet (0-1m3/h)











• Measurements type:

• visualization












• visualization

• pressure fluctuations (30 mm before and after the cone)












• visualization

• pressure fluctuations (directly before and after the cone)

• LDA (47,5 mm downstream the blade – axial and circumferential

velocity profiles)

LDA












• visualization


• LDA (downstream the blade axis)

• PIV (in the cone)












• visualization


• LDA (downstream the blade axis)

• PIV (in the cone)

• Aim:

• to obtain different velocity profiles / swirl distributions

• test the idea to control vortex rope with axial water jet

• to use the data for further research





Numerical setup

• Computational domain

• with swirl generator

• only downstream the swirl generator

• Mesh

• not exaggerate with mesh size → different meshes up to 2Mil. (for

case with swirl generator)

• the same was used as in the previous studies with in-house code

• software – ICEM (hexa)





• boundary conditions

• numerics (see Dellenback Abrupt Expansion OpenFOAM case study)

• Turbulence models: standard k-ε, kOmegaSST, kOmegaSSTF (filtered

kOmegaSSTF), wall function

• unsteady calculations with transientSimpleFoam (initialized with steady

ones)

Variable Inlet Walls Outlet

U profile1DfixedValues fixedValue(0 0 0)

zeroGradient

p zeroGradient zeroGradient fixedMeanValue

k 1,5(Ua*0,05)^2 zeroGradient zeroGradient

ε k^1,5/lt(lt=0,1R)

zeroGradient zeroGradient

ω k^0,5/(0,09lt) zeroGradient zeroGradient

νt/ν 35,6

Numerical setup





Numerical results• Case with swirl generator

• position 1






• position 2






• reason for discrepancy – extensive zone of separation

• will be more investigated





Numerical results

• Case without swirl generator

• averaged LDA measurements as inlet profile

• blades 30° opening

• Q = 25 and 40 m3/h

• no jet

• modified inlet profile from the complete simulation (previous

study with in-house code)

• blades 30° opening

• Q = 45 m3/h

• no jet





Numerical results

• Q = 25 m3/h

k-ε SST SSTF





Numerical results

• Q = 40 m3/h

k-ε SST SSTF





Numerical results

• Q = 40 m3/h

k-ε

SST SSTF





Comparison

Discharge [m3/h]

Frequency [Hz]

Amplitude [bar]

Simulation Experiment Simulation Experiment

sst sstf sst sstf

25 9,39 10,99 8,54 0,0022 0,0016 0,002

40 14,39 14,55 13,49 0,0067 0,0071 0,007

Discharge [m3/h]

Strouhal nr.[-]

Simulation Experiment

sst sstf

25 0,54 0,63 0,495

40 0,52 0,52 0,488





Numerical results

• Q = 45 m3/h, modified inlet profile

LRR

RSMLaunder-Gibson

RSM





Conclusion

• Presentation of IHS test rig – measurements can be

used for further research / test case

• Test rig and swirl generator

• Different operational points numerically simulated

• Investigation of turbulence models

(kOmegaSST, kOmegaSSTF)

• Comparison with experiments → good agreement





Acknowledgements

• To our colleagues, guest researchers, guest students and students

who has been doing the measurements

• All OpenFOAM community





Thank you for your attention !



Numerical investigation of the swirling flow and the...

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