Experimental and numerical study of the tip vortex …SHF Conference on Cavitation, Hydraulic...

SHF Conference on Cavitation, Hydraulic Machines. Air in Water Pipes.

June 5-6th, 2013, Grenoble, France

Experimental and numerical study of the tip vortex (Application to Kaplan Turbine)

J.Decaix, (HEVS) M. Dreyer, (LMH-EPFL) C. Münch-Alligné, (HEVS) M. Farhat, (LMH-EPFL)

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OVERVIEW OF THE PRESENTATION

1.Hydronet 2 Project 2.Experimental Part 3.Numerical Part 4.Experiment vs Numerical 5.Conclusion

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Hydronet 2 Project

Multidisciplinary consortium

Simulation of sand erosion

Tip vortex cavitation

Instability of pump-turbine

HydroPower design

Plant monitoring

To improve the Design, Manufacturing and Operation of HydroPower Plants

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TIP VORTEX CAVITATION (TVC)

Problematic: • Tip vortex cavitation → severe erosion in axial turbines • Origin: vortex roll up in the gap at the tip of the blades • Remedy (anti-cavitation lip): inefficient • Influence of gap width? • Scale up rules? (actual model tests not reliable)

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TIP VORTEX CAVITATION (TVC)

Goals : Experimental and numerical investigations of TVC for a better understanding of the physical phenomena Case study: Naca0009 hydrofoil with variable gap width

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EXPERIMENTAL PART

Tools : • Stereo PIV (Particle Image Velocimetry)

Goals : Measure the tip vortex velocity field for various operating conditions:

• Inlet velocity: 5 m/s → 20 m/s • Incidence angle: 3° → 12° • Gap width: 0 mm → 20 mm

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EXPERIMENTAL PART Stereo PIV setup:

• LMH cavitation tunnel

• Hydrofoil: Naca0009

• Variable gap width

• 200 mJ YAG laser

• Seeding particles: 20 µm hollow glass spheres

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EXPERIMENTAL PART

PIV working principle:

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EXPERIMENTAL PART Stereo PIV principle:

Need of a proper optical calibration!

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EXPERIMENTAL PART Stereo PIV setup:

Combining the left and right velocity field: 3D velocity field

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EXPERIMENTAL PART Velocity field processing:

• Correction of vortex wandering • Mean velocity and vorticity field calculation

Instantaneous Vortex center

Realignment of velocity field before averaging!

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NUMERICAL PART

Goals : To perform the numerical simulations of the experimental cases

Tools : • Ansys CFX 14.0 commercial solver • OpenFoam 2.1.0 open source solver

Modelling : Reynolds Average Navier-Stokes computations coupling with standard two-equations turbulence models : k-ε or k-ω SST

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FIRST COMPUTATIONS Configurations :

• Incidence angle : α = 10° • Inlet velocity : Uinlet = 5.4 m/s or 10.2 m/s Regap ≈ 105

• Gap value : 5 mm, 10 mm and 15 mm

Mesh : 2.9 millions of points with 30 points in the gap

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COMPARISON BETWEEN SOLVERS Position of the tip vortex measured from the maximum of the Q-criterion

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Configuration: U = 10.2 m/s , α = 10°, gap = 10 mm



Q-Criterion

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z

y

Definition

Q = 1/2 (||Ω||2 −||S||2)

With: • Ω: Rotation rate tensor • S: Strain rate tensor



COMPARISON BETWEEN SOLVERS

Vertical position of the tip vortex downstream the Naca

Configuration : • Uinlet = 10.2 m/s • α = 10°

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COMPARISON BETWEEN SOLVERS

Spanwise position of the tip vortex downstream the Naca

Configuration : • Uinlet = 10.2 m/s • α = 10°

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COMPARISON BETWEEN COMPUTATIONS AND EXPERIMENT

Comparisons : • Done on a plan located 35 mm downstream the

trailing edge x = 85 mm

• Focus on the velocity and vorticity fields

• Position of the vortex core determined from the axial

vorticity

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AXIAL VORTICITY

Experiment Computation (OpenFoam)

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Configuration: U = 10.2 m/s , α = 10°, gap = 10 mm



VORTEX POSITION Configuration: α = 10° ; U = 10.2 m/s ; Gap = 10 mm



CONCLUSION AND OUTLOOK

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Experimental Part PIV set up with correction of the wandering motion Acquisition of data for several flow configurations Analysis of the velocity and vorticity fields evolution with

tip vortex confinement

Numerical Part Comparison between CFX 14.0 and OpenFoam 2.1.0 for

different flow configurations Comparison between solver results and experimental data

for different flow configurations

FUTURE A deeper investigation of the tip vortex in cavitating and non-cavitating configurations

Experimental and numerical study of the tip vortex …SHF Conference on Cavitation, Hydraulic...

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