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
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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
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PROPULSION Numerical Approach: General Settings
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• 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
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Transient: ± 4M Cells
Cavitation: ± 8M Cells
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PROPULSION Numerical Approach: Transient Development
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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
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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.
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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
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PROPULSION Model Scale: Cavitation Experiment
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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
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221
propw
vwatm
nD
phgp
Experiment: σ = 2.4 & J=0.5
Free Sailing Flow Conditions
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PROPULSION Model Scale: Cavitating Flow Behaviour
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Simulation: σ = 2.4 & J=0.5
Free Sailing Flow Conditions
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PROPULSION Model Scale: Cavitating Flow Behaviour
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Simulation: σ = 2.4 & J=0.5
Free Sailing Flow Conditions
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PROPULSION Model Scale: Qualitative Comparison
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PROPULSION Effect of Gravitation on Cavitation
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Without Gravity With Gravity
Pressure
Vapour Fraction
increase
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PROPULSION Full Scale Analysis
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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.
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Full Scale Analysis
Absolute Pressure Vapour
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PROPULSION Full Realistic Scenario: Integral Approach
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Air
Water
Boundary Layer
Pressure
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PROPULSION Cavitating Source Term Analysis
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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
VapourFraction_point+150.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour
VapourFraction_point+160.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour
VapourFraction_point+170.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour
VapourFraction_point+180.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour
VapourFraction_point+190.0deg_1.7m Monitor: Maximum of Volume Fraction of Phase H2O_vapour
VapourFraction_point+200.0deg_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.
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Conclusions