Detached eddy simulation of cloud cavitation on tip ... · modified propellers in ship wake fields”, smp’15, Austin, USA, 2015 •Shin, K.W. and Andersen, P., “FD analysis of

07.03.2016© MAN Diesel & TurboDES of cloud cavitation on tip-modified propellers < 1 >

Detached eddy simulation of

cloud cavitation on tip-modified propellers

Keun Woo Shin Propeller & Aftship R&D Department, MAN Diesel & Turbo

Frederikshavn, Denmark


Introduction – Cloud Cavitation (1)

Based on former publications

• Shin, K.W., Regener, P.B., Andersen, P., “Methods for cavitation prediction on tip-modified propellers in ship wake fields”, smp’15, Austin, USA, 2015

• Shin, K.W. and Andersen, P., “CFD analysis of cloud cavitation on three tip-modified propellers with systematically varied tip geometry”, 9th Int. Symp. on Cavitation, Lausanne, Switzerland, 2015



Cloud cavitation on ship propellers

• Intensive noise and mental surface erosion → Unacceptable for ship propellers

• Extensive sheet cavitation← High incident angle and low ambient pressure

• Sheet cavitation detachment← re-entrant jet (turbulent eddy)

• Periodic oscillations of incident angle



Cloud cavitation on ship propellers

• Leading-edge sheet cavitation extension in a high hull-wake region

← Incident angle increase and lowered hydrostatic pressure

• Detachment of sheet cavitation in a form of cloud cavitation

• Conversion of sheet cavitation into tip vortex cavitation


CFD Setup (1)

CFD solver

• STAR-CCM+® 9.02

• DES with k-ω SST turbulence model← Better prediction of detached cavitationthan RANS

• Imcompressible flow solver

• Volume of fluid (VOF) model

• Eulerian multiphase model

• Multiphase interaction→ Cavitation model based on Rayleigh-Plesset equation

• Gravity → Hydrostatic pressure

Cavitation estimations by RANS and DES

(Shin, K.W., (2014), “Cavitation simulation on Kappel

propeller with a hull wake field”, NuTTS2014, Marstrand,

Sweden )

RANS DES

40°

60°


CFD Setup (2)

CFD model

• Rotating domain around a propeller model with D=0.25 m

• Rigid body motion and sliding mesh

• Rudder model outside the rotating domain

• Trimmed hexahedral mesh

• Δx=0.5-1.0 mm on wall surface and Δx=0.1-0.5 mm on blade edge

• 6 prism layers and Δh=0.12-0.25 mm on wall surface → mostly y+≤1


CFD Setup (3)

CFD model

• Mesh refinement in region with sheetcavitation detachment← Volumetric control

• Unsteady computation with 1° propeller rotation per Δt → 116 μs > order of 10 μs for collectivebubble collapse duration← Practical indication of cloud cavitationrisk


CFD Setup (4)

Hull wake model

• Axial wake applied to velocity inletboundary located 3 propeller diameters upstream

• Transverse wake applied by usingmomentum source 1 propeller diameter upstream

Original

hull wake


CFD Setup (5)

Hull wake model

• Wake model test without a propeller model→ Accurate modeling of axial wake→ Characteristic bilge vortex→Deviation in modeling upward flow

Original

hull wake

Wake

model


Propeller models

Reference propeller

• 4-blade Kappel propeller with Ae/Ao=0.38

• Cavitation tunnel test showingextensive sheet & cloud cavitation

Two other propellers

• Modified from the reference propeller by varying tip loading

• Blade pitch variation → 10%, 35%, 60% tip pitch reduction

• Vertical incliation variation

0.6 0.8 1 1.2

0.4

0.6

0.8

1

s/R

P/D

Reference

High tip loading

Low tip loading


Cavitation simulations (1)

Validation against experimentresults

• Cavitation tunnel test with ship hullin SSPA, Gothenburg, Sweden

• Tunnel flow speed = 4.5 m/s, propeller speed = 24 rps, cavitation number = 3.8

• CFD cavitation interface of vaporvolume fraction = 0.1

• Cavitation starting at ϕ≈340°

• Sheet cavitation extention

Exp

CF

D

ϕ=340° 0° 20°



Validation against experimentresults

• Super-cavitation at 0.9R-1.0R

• Detachment of sheet cavitation

• Large structure of cloud cavitationin CFD ← Volume mesh of Δx≈0.5 mm

• Cavitation disappearance at ϕ≈90°E

xp

CF

D

ϕ=40° 60° 90°



High tip-loading propeller

• Sheet cavitation reduction at 0.7R-0.9R ← Lowered propeller speed by 0.5 rps

• Tip vortex cavitation (→0.5% lower propeller efficiency) and reduced cloud cavitation

Reference High tip-loading



Low tip-loading propeller

• Sheet cavitation increase ← Increased propeller speed by 0.5 rps

• Increased cloud cavitation

Reference Low tip-loading


Conclusion

Conclusion

• Steeply lowered tip loading→ Cloud cavitationon marine propellers

• Gradually lowered tip loading→ Prevention or reduction of cloud cavitation→ Propulsive efficiency lossfrom tip vortex

• Optimization of blade tip loadingin marine propeller design

• DES cavitation simulations → Practical tool for predictingcloud cavitation

ϕ=

40

°ϕ

=60

°

Reference

High

tip loading

Low

tip loading

• Hull wake modeling by velocity inlet & momentum source→ Effective way for applying hull wake without a hull 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

Detached eddy simulation of cloud cavitation on tip ... · modified propellers in ship wake fields”, smp’15, Austin, USA, 2015 •Shin, K.W. and Andersen, P., “FD analysis of