Keun Woo Shin, Rasmus Møller Bering - Siemens · Keun Woo Shin, Rasmus Møller Bering . MAN Diesel & Turbo . Frederikshavn, Denmark . Unsteady cavitation simulation on Kappel propeller

17.03.2014 © MAN Diesel & Turbo Unsteady cavitation simulation on Kappel propeller with a hull wake field < 1 >

Unsteady cavitation simulation on Kappel propeller with a hull wake field

Keun Woo Shin, Rasmus Møller Bering MAN Diesel & Turbo Frederikshavn, Denmark

17.03.2014 © MAN Diesel & Turbo Unsteady cavitation simulation on Kappel propeller with a hull wake field

Innovative tip-modified propeller

Tip smoothly curved towards the suction side of blade - Tip swept along the vortex shedding

Non-planar lifting surface - Lifting surface is curved by orthogonal lifting line - Nose-tail line is vertically inclined

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Introduction- Kappel propeller


Reduction of tip vortex loss in the same principle as airplane winglet → Higher propulsive efficiency

Reduction of pressure pulse on hull structure ← Tip bending blocks radial propagation

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Kappel propeller in EU project ’Kapriccio’ is handled Andersen P., Friesch J., Lundegaard L., Patience G., Development of a marine propeller with nonplanar lifting surfaces, Marine Technology, Vol.42, No.3, 2005 - Self-propulsion tests and cavitation tests for conventional & Kappel propeller s on a container ship and a tanker - Sea trial and cavitation observation of full-scale conventional & Kappel propellers

CFD simulation of a fully wetted flow on Kappel propeller has been made with a hull wake field Shin K.W., Andersen P., Bering R., CFD simulation on Kappel propeller with a hull wake field, Numerical Towing Tank Symposium, 2013

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Propeller flow simulation

Propeller design phase: - Single-blade model with periodic boundary - Steady-state computation with MRF - Uniform inflow for open-water condition - Radially-varying and circumferentially uniform inflow for behind-hull condition - RANS solver with k-ω SST turbulence model and Gamma ReTheta transition model - Trimmed mesh with prism layer



Propeller design phase: - Blade is designed by lifting-surface method and vortex lattice method - Blade geometry is prepared by external CAD software - Automatic replacement of blade model by JAVA macro - Domain and mesh size are adjusted according to propeller diameter (e.g. 0.2-0.4%D for blade surface mesh, 0.5%D for volume mesh of tip vortex trace)



Propeller design phase: - 1.5 - 2.0 million cells → Less than 1 hour by 32 nodes of 3.06 GHz processor and infiniband → Practical propeller optimization

- Comparison with open-water model test: Discrepancies < 3.0% in KT, KQ, ηO in design condition

0.2 0.3 0.4 0.5 0.6

0.1

0.2

0.3

0.4

0.5

0.6

J

K T, 10K

Q, ηo

ηo

KT

10KQ

ExpCFD



Final design phase: - Propeller with a rudder - Unsteady computation with rigid body motion - Δt corresponds to 5° rotation per Δt, until the flow is developed (5 revolutions) - 1° rotation per Δt - 5 inner-iterations - 8 – 10 million cells → 20 – 30 hours for 10 revolutions with 32 nodes



Final design phase: - Axial wake field is applied 3D ahead of propeller plane ← Wake measurement is scaled by weff/wnom, where w = 1-Va/Vs, wnom w/o propeller and weff with propeller

- Upward flow corresponding to averaged transverse wake is added ←Transverse wake is characterised by upward flow ← Slanted stern hull shape

- Wake simulation without a propeller is compared to wake measurement → Good agreement in high wake at inner radii and upper part and bilge vortex

Measurement No upward flow Including Upward flow



Final design phase: - Single-blade thrust is periodic and highest at 12 o’clock position ← wake peak

- Comparison with self-propulsion test → Wake fraction is increased by 0.6% to reach the same thrust as in model test → Torque is 4.1% higher → ηB is 4.0% lower → ηO and ηR are 1.3% and 3.6% lower, respectively

0 90 180 270 360

0.03

0.04

0.05

Blade angle [deg]

KTB

on

a si

ngle

bla

de


Cavitation simulation

BEM (Boundary Element Method) - Used for cavitation estimation in blade design phase - All three wake components are applied - Pressure distribution on blade surface is calculated every 5° blade position - Low computational effort ← about15 min - Coarse mesh → insufficient resolution for blade edge curvature

Pressure from BEM Blade mesh in BEM Blade mesh in CFD



BEM (Boundary Element Method) - Comparison of chordwise pressure distribution in BEM and CFD - Pressure distribution deviates at leading and trailing edges - Deviation at inner radii ← No hub in BEM

0 0.2 0.4 0.6 0.8 1

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

x/C

-Cp

0.4R

0 0.2 0.4 0.6 0.8 1-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

x/C

-Cp

0.6R

0 0.2 0.4 0.6 0.8 1-3

-2

-1

0

1

2

3

4

5

6

x/C

-Cp

0.8R

BEM (Pressure)BEM (Suction)CFD (Prsessure)CFD (Suction)



CFD - RANS solver with k-ω SST turbulence model and Gamma ReTheta transition model - Hull wake field - Cavitation model (←Rayleigh-Plesset equation) and VOF model - Seed density = 1.5∙1012m-3 and diameter=5∙10-6m → Cavitation growth rate - Hydrostatic pressure → initial & outlet pressure - Ambient pressure (reference pressure) ← cavitation number - Fixed vapor pressure

Cavitation tunnel test - Ship model - High propeller revolutions of 30 Hz - Tunnel flow speed and pressure are adjusted for a given set of thrust and cavitation number



CFD - Iso surface of 10% vapor - Unsteady sheet cavitation in upper part of propeller disk - No vortex cavitation in CFD ← insufficient volume mesh refinement along vortex trace - Vorticity magnitude indicates tip vortex



- CFD overestimation at tip ← difference in thrust - CFD underestimation at 0.7R-0.8R ← difference in hull wake - BEM underestimation ← no cavitation convection

Blade angle

= 160°

Blade angle = 180°

Experiment CFD BEM



- CFD overestimation ← difference in thrust - Leading-edge cavitation at 0.7R-0.9R in BEM ← insufficient resolution of leading edge curvature

Blade angle = 200°

Blade angle = 220°

Experiment CFD BEM



- BEM has differences in cavitation inception and termination ← insufficient resolution of leading edge curvature - CFD has earlier inception and later termination ← difference in thrust

Experiment Blade angle=140°

CFD 130°

BEM 90°

Inception

Termination

240° 260° 300°



Conclusion - CFD simulation has acceptable accuracy for estimation of unsteady propeller cavitation behind hull - It needs more validation cases to ensure robustness and consistency for quantative estimation of cavitation - It is necessary to economize computational model and run it with more than 100 nodes for practical cavitation simulation on propeller design phase

Future work - Propeller optimization based on CFD with respect to propulsive efficiency and cavitation safety - CFD estimation of propeller noise & vibration by aeroacoustics model - Tip vortex cavitation simulation by Lagrangian multiphase model


Thank You for Your Attention!

All data provided in this document is non-binding. This data serves informational purposes only and is

especially not guaranteed in any way. Depending on the subsequent specific individual projects, the relevant

data may be subject to changes and will be assessed and determined individually for each project. This will depend

on the particular characteristics of each individual project, especially specific site and operational conditions.

Documents

Keun Woo Shin, Rasmus Møller Bering - Siemens · Keun Woo Shin, Rasmus Møller Bering . MAN Diesel & Turbo . Frederikshavn, Denmark . Unsteady cavitation simulation on Kappel propeller