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STAR Global Conference 2016, March 7th-9th, Prague, Czech Republic.
CFD Simulations for Ships with Rotating Propeller- Self propulsion, Cavitation & Ship radiated noise -
NMRI, Tokyo JAPANN.Sakamoto and H.Kamiirisa
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http://www.aukevisser.nl/inter-2/id427.htm
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Table of Contents
1.Background and objective2.Overview of CFD solver3.Test cases4.Computational setup5.Results and discussion6.Concluding remarks
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1. Background
Propulsive performance of commercial vessels→ EEDI regulations (IMO)→ Design exploration in… Hull form Energy saving device Propeller
Powering estimationby CFD→ Complex geometry/physics Grid generation Propeller-hull interaction
over
over
Class NK Annual Fall Seminar (2012)
Kawakita et al. (2012) Japan Shipbuilding Digest (2013)
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1. Objective: Propulsive performance
1:CFD analyses in… Resistance and self-propulsion Propeller open water
2:Validation in… Self-propulsion factors (SPFs) Local flow field in model scale
3:Estimate… Effect of energy saving device Accuracy of the present methods
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1. Background
Propeller cavitation and noise→Marine environmental protection
Regulations→ICES CRR No.209 (1995)→IMO MEPC.1/Circ.833 on 2014.→For commercial ships, yet non-mandatory→Regulate SPL (ICES)→Regulate Kpi (IMO): Kp1≤3kPa, Kp2≤2kPa for CB<0.65Kp1≤5kPa, Kp2≤3kPa for CB>0.65
ICES
Kamiirisa and Goto (2005)
Merchant ship in St.Lawrence at 1 mile
(http://ocr.org/portfolio/shipping-noise/)
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1. Objective: Propeller cavitation and noise
1:CFD analyses in… Propeller performance Propeller cavitation
2:Validation in… Cavitation pattern Near field cavitation noise in model and full scale Feasibility of empirical formula with CFD
3:Understand… Present capability of CFD to ship radiated noise
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2. Overview of CFD solver
STAR-CCM+® 10.06 (double-precision ver.) k-ω SST (all turbulent), DES for cavitation in fine grid
- Low Rn near wall treatment (y+~1) Cavitation model by Schnerr and Sauer (2001)
- NO hydrostatic component at this time VoF for interface capturing Overset for propeller rotation SIMPLE for v-p coupling MPI parallelization 2nd order in space Propeller rotation in… →3deg(self-propulsion), 1deg(cavitation) per time-step.
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3. Test cases: Propulsive performance
Japan Bulk Carrier (JBC)Hull (model scale)
Lpp(m) 7.0
B (m) 1.125
d (m) 0.4125
CB 0.858
Propeller (MPNO.687)
Dp (m) 0.203
aE 0.500
P/D 0.750
Z 5
Blade section AU
Geometries and exp. data open to public at
http://www.t2015.nmri.go.jp/jbc.html
Energy saving duct at stern
Resistance and self-propulsion data
Local flow measurement by PIV
→ without/with propeller rotation!
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3. Test cases: Propeller cavitation and noise
Propellers for “TS Seiun-1st”
CP HSP2
Dp (m) 0.221 0.220
aE 0.650 0.700
P/D 0.950 0.944
Z 5
Blade section Mod. MAU Mod. SRI-B- Decreased pitch
- Tip-unloaded
HSP2 retrofitted after CP to reduce hull vibration
Both model and full scale measurement data
available.
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4. Computational setup: Propulsive performance
Flow condition (based on CFDWS Tokyo 2015)(Fn, Rn)=(0.0, 7.46E+06), np(rps)=7.8(w.o. duct), 7.5(with duct)
Grid→trimmed cell, overset→”linear” scheme for calculatinginterpolation coefficients fromdonors to receptors.→”flux correction” activated.
Stator(hull) 2.02M
Rotator(prop.) 3.95M
Total 5.97M
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4. Computational setup: Propeller cavitation and noise
Flow condition (based on Kudo et al. 1989)
Grid (sliding/overset)
np(rps) Rn(kempf) KT σn
CP20.0
6.5E+05 0.207 3.06
HSP2 7.0E+05 0.201 2.99
0.7Dp
(Hasuike et al. 2010)
Local refinement to resolve sheet and tip-vortex cavitation
Approx. 19M cells in total.
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5. Results: Propulsive performance
Effect of the duct to resistance and SPFs
Ctmx10-3 Exp. CFD
w.o. duct 4.289 4.160
with duct 4.263 4.131
KT-identity method for self-propulsion analysis
• Relative difference very well predicted!→Contribute for further design explorations.
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5. Results: Propulsive performance
Thrust distribution (θ=0o, 24o, 48o), back side
• Pitch distribution can be increased up to r/R~0.6 for the propeller WITH duct. →np may decrease yet yields the same thrust.
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5. Results: Propulsive performance
Vortical structure
• Tip and hub vortices are the same.
• Flow separation at the bottom of the duct
→ wake gain→ valid in full scale?• Difference in vortices
behind the propeller→ effect of np?
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Cavitation pattern (Void fraction=0.1)
5. Results: Propeller cavitation
• Sheet cavitation well resolved, TVC needs more resolution.• Phase & amplitude difference in Kp and Vc due to skew.
Nuclei radius=1.0e-6(m)
Nuclei density=1.0e+14(1/m3)
←Click to animate
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Validation in cavitation extent
5. Results: Propeller cavitation
port starboard port starboard
Exp.data: Kurobe et al. (1983)
θ=0° θ=20° θ=40° θ=60° θ=0° θ=20° θ=40° θ=60°
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Overview of the validation data (SR183 Final report)
5. Results: Propeller cavitation noise
Wire mesh wake
in model scale
B&K 8103
B&K 8103 Levkovskii’s scaling law (model to full)
Brown’s formula for empirical method
K: empirical const. (=163)
B: # of blade, Dp: prop.dia., AD: blade area
n=163rpm in full scale
σns= σnm
Geo-sym hydrophone location
Compute Ac/AD by CFD!
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Direct estimation from CFD solution
5. Results: Propeller cavitation noise
Tonal noise well resolved.Relative difference between CP and HSP2 captured well in tonal noise.(∵Wake and sheet cavitation patterns are well reproduced.)Broadband noise are fair.(∵Bubble growth and collapse cannot be well resolved.)
Model scale
Full scale
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Indirect estimation from CFD(model scale)+Brown’s formula
5. Results: Propeller cavitation noise
Brown’s formula gives appropriate upper-bound.(∵Ac/AD well predicted.)
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Propulsive performance• Still needs diagnostics in POT (both exp. and CFD)• Relative difference in SPFs very well predicted with and
without duct configurations.• Local physics helps for design exploration.
Propeller cavitation noise• Sheet cavitation pattern well predicted.• Quantification of cavitation extent feasible by CFD.• Tonal noise well predicted.• Broadband noise fair, yet empirical formula is still useful
together with CFD.
6. Concluding remarks