rans simulations of cavitating azimuthing...

Maarten Bijlard

RANS Simulations of Cavitating

Azimuthing ThrUSTERS

STAR Global Conference 2014

© Wärtsilä

PROPULSION

17-19 March 2014 STAR Global Conference 2014. Maarten Bijlard 2

Contents

• Brief Introduction on:

– Steerable Azimuthing Thrusters

– Developments of Numerical Flow Simulations

• Numerical Approach and Assumptions

• Cavitation

– CavitatingTunnel Experiments

– Model Scale Simulations

– Full Scale Simulations

• Future Developments of Cavitating Flow Simulations

– Integral Approach

– Qualitative Perspective

• Conclusions and recommendations

© Wärtsilä

PROPULSION Introduction – Steerable Azimuthing Thrusters

• Wartsila FS3510 figures: 3.9 meter propeller / 4500–5500 kW input power.

• The steerable thrusters are often used for dynamic positioning (DP) of

drilling rigs, though transient conditions might be applicable as well.


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PROPULSION Developments of Numerical Flow Simulations

• The increase of the complexity of the CFD simulations for thrusters

is shown over the years.

• The developments in simulations are enormous, due to improved

software and continuous increasing computing power.

17-19 March 2014 STAR Global Conference 2014. Maarten Bijlard

2006:

thruster performance

2008:

thruster blade loads

2010:

tilted thruster concept

2012:

thruster-hull interaction 2013 :

thruster-thruster interaction

THRUST

Vertical

force

Horizontal

force

4

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PROPULSION Wartsila LMT3510 Thruster

17-19 March 2014 5

Advanced strut design

Advanced propeller gearbox design.

New Nozzle design WTN

[Wartsila Thruster Nozzle]

Key features

STAR Global Conference 2014. Maarten Bijlard

Optimized 4-bladed

propeller design with

minimum tip clearance

© Wärtsilä

PROPULSION Numerical Approach: General Settings


• Thruster Geometry: NX 3D-CAD model

•Unstructured Trimmed Hexahedral Cells

•Extrusion Cells in Boundary Layer

•Moving Frame of Reference for Propeller Region

General Mesh Settings:

• STAR-CCM+: Version 7.04

Physics:

•Segregated Flow Solver

•Sauer VOF Cavitation Model:

1. Default Settings, except seed density is reduced to 10-14 m3/s

for model scale simulations.

•Realizable k-ε model:

1. High y+ wall treatment

2. Temporal discretization first order

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PROPULSION Numerical Approach: Mesh Settings


Transient: ± 4M Cells

Cavitation: ± 8M Cells

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PROPULSION Numerical Approach: Transient Development


Transient: ∆φ ≈ 2◦

Cavitation: ∆φ ≈ 0.2◦

Small Angular Steps

∆φ ≈ 0.2◦

Vapour Fraction

Running time: 1-2 days 8-15 days (35 cpu’s)

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PROPULSION Validation: Model Scale Testing

• Model tests carried out by Marintek Norway

– Propeller diameter 250 mm

– Speed 16 Hz

• Conditions

– Standard open water (straight course)

– Oblique inflow

– Dynamic steering events

– Cavitation tests

17-19 March 2014 9 STAR Global Conference 2014. Maarten Bijlard

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PROPULSION Validation: Open Water Performance

• Model scale performance for straight unit – 4500 kW

• Comparison measurements and model scale CFD

• Good agreement for thrust, torque and efficiency over complete J-range,

including the bollard pull condition.


0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ktp

, Ktt

, Kq

, Eta

0 [-

]

Dimensionless advance speed J [-]

Comparison CFD-results with model scale experiments for straight unit

Ktp-CFD

Ktt-CFD

Kq-CFD

Eta0-CFD

Ktp-EXP

Ktt-EXP

Kq-EXP

Eta0-EXP

efficiency

total thrust

propeller thrust

propeller torque

© Wärtsilä

PROPULSION Model Scale: Cavitation Experiment


221

propw

vwatm

nD

phgp

Experiment: σ = 2.4 & J=0.5

Free Sailing Flow Conditions

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PROPULSION Model Scale: Cavitation Experiment


221

propw

vwatm

nD

phgp

Experiment: σ = 2.4 & J=0.5


© Wärtsilä

PROPULSION Model Scale: Cavitating Flow Behaviour


Simulation: σ = 2.4 & J=0.5


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PROPULSION Effect of Gravitation on Cavitation


Without Gravity With Gravity

Pressure

Vapour Fraction

increase

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PROPULSION Full Scale Analysis


Absolute Pressure Vapour

• Full scale CFD calculations for 4m draught

(corresponds to σ=2.4 or 1 Diameter water column above shaft line)

• Only a limited amount of cavitation is found for this condition.

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PROPULSION

• Full scale CFD calculations for 4m draught

(corresponds to σ=2.4 or 1 Diameter water column above shaft line)

• Only a limited amount of cavitation is found for this condition.


Full Scale Analysis

Absolute Pressure Vapour

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PROPULSION Cavitating Source Term Analysis


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-36.0000 -26.0000 -16.0000 -6.0000 4.0000 14.0000 24.0000 34.0000

Vap

ou

r Fr

acti

on

[-]

Angle [degrees]

Vapour Fraction 1.7m

VapourFraction_point+140.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour







PP

Dt

DR sat

32

2

Rayleigh-Plesset:

Temporal Accuracy Tests: dS

ddt

d

v

v

Cavitation Erosion: Potential Power Evaluation

Implosion Source Monitoring Flow Parameters

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PROPULSION

• The applied CFD methods provide good results between experiments

and simulations.

• Apart from typical scaling effects, the solutions of model and full scale

simulations are nearly identical.

• The knowledge of cavitating flow behavior, such as cavitation erosion,

may be better understood once a more quantitative approach is further

developed.

• The first step towards numerical flow simulations of azimuthing thrusters

has been made and the results are promising, so the journey continues.


Conclusions

rans simulations of cavitating azimuthing...

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