04/21/23 © 2012 UNIVERSITY OF ROSTOCK | FACULTY OF COMPUTER SCIENCE AND ELECTRICAL ENGINEERING

On Optical Quantification of Cavitation Properties

Stefan BorchertWillfried KrögerStephan HöhneNils DamaschkeZhiliang Zhou

Institute of General Electrical Engineering University of Rostock

CAV 2012, Singapore, 13.08.-16.08.2012

Institut für Allgemeine Elektrotechnik

KonKav I project (funded by BMWI)

Goals – Quantitative water quality

measurements– Quantitative cavitation property measurements

Imaging techniques– Shadow imaging – Laser calibration

Project partners– Hamburg Ship Model Basin (HSVA)– Potsdam Model Basin (SVA)– Technical University of Hamburg Harburg (TU-HH)– University of Rostock (URO)

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1. Lighting and cameras

Requirements

Diffuse lighting– Transmitted light (with diffusor)– Diffuse reflection– Glaring reflection– Direct lighting

Object lens– Small depth of focus -> large apterture – Large depth of focus -> small aperture

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Best Quality

Worst Quality

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1. Lighting and cameras

Diffuse Reflector

Shadow imaging camera

Stroboscope

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2. Shadow imaging – cavitation thickness

Large aperture

2D foil

Sharp plane

Perspective view

Optical axis

Tunnel Window

WATER AIR

Sheet caviatation

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2. Shadow imaging – cavitation thickness

2D foil – no cavitation 2D foil – with cavitation

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1 pixel = 40µm 1392x1040 pixel

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2. Shadow imaging – cavitation thickness

Occurrence of detected edges Extracted cavitation edges

Max

Mean

Min

Foil

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1 pixel = 40µm 1392x1040 pixel

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3. Laser calibration

Average laser position Laser position regression

Required to convert image coordinates to physical coordinates- Physical step size is known (traversed by defined distance)- Laser also used to set depth of focus position

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2 stereometric cameras – identical object lens

4. Shadow imaging – tip vortex

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4. Shadow imaging – tip vortex

Propeller blade tip Binary representation

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1 pixel = 70µm 1392x1040 pixel

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4. Shadow Imaging – tip vortex

Example frames Color coded occurence

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1 pixel = 70µm 1392x1040 pixel

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5. Experimental results – 2D foil

Occurrence of detected edges

Extracted cavitation edges

inception σ=3 σ=2

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5. Experimental results – tip vortex

Occurrence of tip vortex – Stereo 1 (straight)

inception σ=3 σ=2

Occurrence of tip vortex – Stereo 2 (tilted)

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Conclusions

Limited optical access poses challenges– Non-tilted viewing angle if possible– Transmitted light if possible

Intermittent cavitation behavior poses challenges– Analyze temporal occurrence– Capture a large number of frames

Cavitation can be quantified– Laser calibration enables coordinate conversion

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Thanks for your attention

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