Experimental Investigation of Cavitation and Erosion at ...s3-eu-west-1.amazonaws.com/foreninglet-wordpress... · Model testing scaling laws ...for cavitation testing StagnationPressure

May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen

1

Dansis Seminar on

Erosion and Cavitation

Bjerringbro (DK)

May 22, 2019

Christian Johannsen

Hamburg Ship Model

Basin (HSVA)

Bildbereich

Experimental Investigation of Cavitation and

Erosion at HSVA – The Hamburg Ship Model Basin

2

Who is HSVA?

Cavitation in Shipbuilding and its Aftereffects

Model Testing Technique and its Transferability to Reality

HSVA‘s New Erosion Testing Method

Summary

Outline



3

Who is HSVA?

Research based services for the maritime industry:

Model tests in open water

and in ice

Computational fluid

dynamics

Design and analysis

Full scale investigations

4

Private, self supporting company

Owned by German Shipping Industry

21 shareholders

100 employees

12 million € turnover per year

83% commercial orders

Internationally acting

43% National

57% International

17% Research

83% Industry


Who is HSVA?

5

Predictions for...

• Power requirement of ships

• Propeller cavitation behavior, noise and vibration excitation, ersoion

• Manoeuvring behavior of ships

• Seakeeping behavior of ships

• Ice-breaking performance of ships

Design, analysis and optimisation of

• Hull lines

• Propeller geometries

• Ship appendages (ruders, fins, etc.)

Tailor-made studies to all questions around ship hydrodynamics


What is HSVA doing?

6

What tools do we use?

1.

2.

300 m long towing tank

Computer Cluster 80 m long ice tank

Cavitation tunnel for complete ship

models


7

The towing tank

300 m x 18 m x 6 m


8

The cavitation tunnel HYKAT

Test section dimensions 11 m x 2.8 m x 1.6 m


9

The ice tank

78 m x 10 m x 2.5/5.0 m


10

The computer cluster


90 nodes, 1500 cores

11

Who is HSVA?




Summary

Outline


12

Cavitation in shipbuilding and its aftereffects


At school they taught us:

Water vaporizes at 100°C – but is that true?

13

If pressure is low enough, even cold water vaporizes

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80 100

Water Temperature [° C]

Va

po

ur

Pre

ssu

re [b

ar]

Atmospheric Pressure at Sea Level

Possible Pressure at

Propeller Suction Side

Atmospheric Pressure at Mount Everest



14

n D

–

VA

+

+

+

–

–

–

On the propeller blade May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen


24. Oktober 2011 Kavitationskolloquium Ruhr-Universität, C. Johannsen

15

n D

VA Vt

+

+

+

–

–

–

–



On the propeller blade

16

n D

VA Vt

+

– –

–

– +

+

Sheet cavitation



On the propeller blade

17

–

VA Vt

+

+

+ –

–

–

n D

At the blade tip

Tip vortex cavitation



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Erosion May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen


19 May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen


Cavitation causes pressure variations propagating to the hull

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Full Scale Radiated Noise

60

70

80

90

100

110

120

130

140

150

160

100 1000 10000

Frequency [Hz]

So

un

d P

res

su

re L

ev

el [d

B r

e 1

µP

a,1

Hz,R

MS

,1m

]

Limit Curve

Noncavitating Condition

Cavitating Condition Full Scale Radiated Noise

Cavitating

Non Cavitating

Noise May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen


Cavitation collapses make noise

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Cavitation needs to be minimized to...

to avoid damages

to avoid vibrations

to avoid noise inboard and outboard


22

Who is HSVA?




Summary

Outline


23

Why not using numerics?



The environment of cavitation is...

three-dimensional

highly turbulent

instationary

influenced by viscosity effects

compressible (vapor phase)

24

H

L

HModel

LModel

For wave generation of a ship:

222

2

2

FnLg

v

Lg

TL

g

TL

g

a

gm

am

ForcesGravity

ForcesMass

Froude Number

ModelShip FnFn !


Model testing scaling laws

Which of these rectagles scale to each other – and why?

The relevant parameters – here length and height – have the same ration

to each other: Model

Model

HL

HL

25

Lg

vWave generation of a

ship Froude No.

Frictional resistance Reynolds No.

Propeller loading Thrust Coef.

Cavitation extent Cavitation No.

ForcesGravity

ForcesMass

ForcesFriction

ForcesMass

Lv

42 Dn

T

2

.

)(2

Dn

PP Vaporstat

PressureStagnation

Press. Vapor toMargin


Model testing scaling laws

PressureStagnation

Prop.atIncr.Pressure

26

Lg

vWave generation of a

ship Froude No.

Frictional resistance Reynolds No.

Propeller loading Thrust Coef.

Cavitation extent Cavitation No.

ForcesGravity

ForcesMass

ForcesFriction

ForcesMass

Lv

42 Dn

T

2

.

)(2

Dn

PP Vaporstat

PressureStagnation

Press. Vapor toMargin


Model testing scaling laws ...for cavitation testing

PressureStagnation

Prop.atIncr.Pressure

by adjustment of tunnel water speed

by reduction of tunnel pressure

27

Hydrodynamics- and Cavitation Tunnel (HYKAT)

27

7 m/s

Pabs. 0.4 bar


Model testing

procedure

28

Hydrodynamics- and Cavitation Tunnel (HYKAT)

28


Model testing

procedure

29

29

Model testing with strobe light


Cavitation behavior of a container ship propeller at strobe light

30

30

Model testing - the drawback of strobe light


31

31



32

32



You can‘t see the cavitation dynamics!

33

Model testing – full scale similarity of cavitation behavior

Model test in HYKAT Real ship


Perfect agreement!

CLT Propeller in HYKAT.avi

CLT Propeller real.avi

34

Model testing – full scale similarity of pressure pulses


Propellererregte Druckschwankungen

1. Harm. 2. Harm. 3. Harm. 4. Harm. 5. Harm.

Dru

ckam

plit

ude

Großausführung

Modell

Almost perfect agreement!

Full scale

Model

Hu

ll P

ressu

re A

mp

litu

de

s

35

Model testing – experience based erosion prediction

• Face cavitation is erosive

• Cloud cavitation is erosive

• Bubble cavitation is erosive

• Root cavitation is erosive

Pros & Cons:

+ Reasonable effort

+ Much experience

+ Accepted method

- Subjektive judgment

- Physically not substantiated


36

Flow

Model testing – high speed video based erosion prediction

Erosive „Focusing Cavity“ on a hydro foil, 30.000 frames per second

Images:

Chalmers Universität/

SSPA, Göteborg

Pros & Cons:

+ Physically substantiated

+ Less subjective

- Extreme effort


37

Model testing – high speed video based erosion prediction

Erosion test result for a fast Patrol Boat


5000 frames per second

38

Model testing – soft ink based erosion prediction


39

Model testing – soft ink based erosion prediction

Erosion test result for a fast Patrol Boat

Pros & Cons:

+ Small effort

+ Physically substantiated

- Depending on surface properties

- Test parameters arbitrary

- Results sometimes ambiguous


sprayed paint sketch from strobe light observation

40

Who is HSVA?




Summary

Outline


41



Wo

rkin

g

ele

ctro

de

Co

un

ter

ele

ctro

de

Electro-chemical deposition

of polymers

Film thickness

proportional to

current and time

Individually shaped

counter-electrode to ensure

homogeneous electric field

0 s 60 s 120 s 180 s 300 s


Tested with ultrasonic oscillator by University of Bochum / Germany

Pros & Cons:

+ Controlled, thin and repeatable film thickness

+ Reduced ambiguity

+ No drying time required

- Individually shaped counter electrode necessary

- Sucessfully tested only on brass props so far

42 May 22, 2019 Dansis Seminar, Bjerringbro (DK), C. Johannsen

43

Who is HSVA?




Summary

Outline


44

Summary

Model tests are still the most reliable tool to predict cavitation behavior and erosiveness for the shipping industry

Much experience is required to evade the pitfalls

A new soft-surface method has improved reliability and repeatability of erosion predictions at HSVA

Documents

Experimental Investigation of Cavitation and Erosion at ...s3-eu-west-1.amazonaws.com/foreninglet-wordpress... · Model testing scaling laws ...for cavitation testing StagnationPressure