This document summarizes a study on cavitation. It discusses types of propeller cavitation, the relationship between cavitation structure and erosion, cavitation erosion fracture mechanisms, and detection of cavitation in ship operation. Experiments were conducted using ultrasonically induced cavitation on common shipbuilding materials to examine mass loss over time and fracture patterns. Acoustic sensors were able to detect cavitation location and intensity on a reduced scale rudder model. The study provides insight into cavitation effects and a method for cavitation source location monitoring on ship rudders.

1. Cavitation
Study
Swapnil Rupaye /
17NA60S03
Pramod k Ram /
17NA60S01

2. CONTENTS
 Introduction
 Types of Propeller Cavitation
 Relationship Between Cavitation Structure and Erosion
 Cavitation Erosion Fracture Mechanisms and Detection in Ship Operation
 Conclusion
 References

3. Introduction
 The formation and
subsequent collapse
of vapor bubbles when
pressure falls below
the vapor pressure of
water.
 Cavitation occurs on
propellers that are
heavily loaded or
having high thrust
loading coefficient.

4. Types of Propeller Cavitation
 Blade Tip Cavitation
Flow velocities at the tip are
fastest so that pressure drop
occurs at the tip.
 Sheet Cavitation
Large and stable region of
cavitation covering the suction
face of propeller

5. Relationship Between Cavitation Structure
and Erosion
 3D Twisted Hydrofoil undergoes cloud Cavitation
 Cavitation structure are synchronously recorded by two
high speed cameras and the status of erosion region is
evaluated by paint loss to estimate relationship between
Cavitation structures and erosion regions
 Test facility and experimental setup
-high speed Cavitation tunnel
- 3D twisted hydrofoil (NACA0009) with chord
length 112.5mm and span length 225mm
before test foil surface coated with paint
- two high speed cameras from bottom and side of
test section

6. Relationship Between Cavitation Structure
and Erosion

7. Evolution of Cavitation
Structure
Top View (U = 14m/s , σ = 1.2) Side View

8. Evolution of Cavitation
Structure
1. Re-entrant flows (marked with arrows) beneath the
sheet form in both side of the rear area of this sheet,
then they move forward to the center of hydrofoil and
gather together in the span wise symmetric plane
2. Subsequently, the converged re-entrant flow cuts off the
cavitation sheet which seems to be the generation
mechanism of large scale cavitation.
3. The detached part of the sheet moves downstream with
the incoming flow and evolves into a U-shaped vortex
structure
4. The U-shaped vortex structure continues to be
convected downstream and damps in the downstream

9. Surface Coating Status Of
Hydrofoil Before And After Test
Before Test After Test

10. Comparison of Cavitation
Structure and Erosion Region

11. Conclusion
 Useful to predict the erosion regions and damage
extent qualitatively
 Most erosive cavitation structure is unsteady rear part
of the sheet cavitation

12. Cavitation Erosion Fracture
Mechanisms and Detection in Ship
Operation
 Study of cavitation erosion in relation to common
shipbuilding materials such as Grade DH36 steel,
Cupronickel & Stainless steel
A. Experimentally finding resulting mass loss
B. Fracture mechanism of erosion on material due to
ultrasonically induced cavitation
C. Identifying cavitation erosion related resonance
D. Relation between obtained stresses and intensity of
cavitation in terms of erosion mass loss
E. Cavitation measurement on reduced scale rudder model
F. Cavitation location using array of acoustic sensors

13. Experimental Set Up
 Ultrasonic transducer – Hielscher UIP
1000hD, 1000W in 50W step, sonotrode
frequency-19.5Hz
 Specimen – 50*50*5 mm of three metals
 Scanning Electron Microscope
 Piezo electric sensor with pre amplifiers,
signal attenuators and detectors
 Fibre Bragg Grating sensor with light
source, photo diode and digital oscilloscope

14. Experimentally Finding
Resulting Mass Loss
 Specimen exposed to ultrasonically
induces cavitation for a period of 5 hours
 Mass loss measurement conducted
every 30 minutes

15. Experimentally Finding
Resulting Mass Loss
 Varying slopes of mass loss lines for 3
materials with cupro nickel exhibiting
highest rate of mass loss followed by
grade DH36 steel and stainless steel
 Total mass loss,
stainless steel : 0.02g
grade DH36 steel : 0.13g
cupro nickel : 0.21g
 So stainless steel 254 exhibit best
cavitation erosion resistance

16. Fracture Mechanism Of Erosion On
Material Due To Ultrasonically
Induced Cavitation
 Specimens examined in SEM for appearance of their
surface
 Eroded surface of
-Stainless steel 254 characterised by transgranular brittle
fracture
- DH36 steel characterised by ridges and smooth bumps
which is typical feature of transgranular brittle fracture
-Cupronickel characterised by ductile dimples of all sizes
which is typical feature of plastic deformation

17. Fracture Mechanism Of Erosion On
Material Due To Ultrasonically
Induced Cavitation
 Type of fracture brittle or ductile experienced by the
materials due to cavitation could be explained by
measuring mass loss

18. Identifying Cavitation Erosion
related Resonance
 Acoustic emission measurements were
conducted using both types of acoustic
sensors piezoelectric and fibre bragg
gratings.
 Frequency response obtained for both
type of sensor is shown in graph
 A common frequency component is
apparent on both frequency domain
spectra. This is the 19.5 kHz resonance
which matches the operating frequency
of the ultrasonic transducer

19. Relation between obtained stresses
and intensity of cavitation in terms of
erosion mass loss
 Four different test rig configurations examined for each
material
 Leading to cavitation of varying intensity ranging from -
Non Erosive
- Slight Erosive
- Medium Erosive
- Highly Erosive
 Sensors are calibrated to give stress in relation to
voltage, σ = k * v

20. Relation between obtained stresses
and intensity of cavitation in terms of
erosion mass loss
Property
(MPa)
Stainless
steel
DH36 steel Cupro
nickel
Yield
strength
415 350 130
Endurance
limit
345 245 140
Non Erosive
stress
320 180 220
Slightly
erosive
stress
350 210 310

21. Cavitation Measurement on
Reduced Scale Rudder Model
 Reduced scale rudder model placed
inside large tank
 Fixed by elastic bands to isolate it
acoustically
 Ultrasonic transducer was placed above
its top surface in 3 different positions as
shown in figure
 Cavitation erosion intensity measured by
piezo electric acoustic sensors

22. Cavitation Measurement on
Reduced Scale Rudder Model
 For Non erosive and slightly erosive
condition gives stress values identical to
small plate
 For higher stress values signal
attenuates with distance so low stress
recorded for position P1 & P3, whereas
position P2 gives stress values identical
to small plate

23. Cavitation Location using
Array of Acoustic Sensors
 Based on principle of triangulation
 Array of three acoustic sensors S0,
S1, S2 and cavitation source used on
rudder model
 Cavitation source lie at intersection of
three circles with radius r, r+δ1, r+δ2
and corresponding centres of those
circle lie at position of sensors
 Circles described by equations:
x2 + y2 = r2
(x-x1)2 + (y-y1)2 = (r+δ1)2
(x-x2)2 + (y-y2)2 = (r+δ2)2
 Total 11 different sonotrode
placements over the surface of
rudder were examined

24. Cavitation Location using
Array of Acoustic Sensors
 Both PZT and FBG are capable of locating cavitation all over the rudder surface
 Slight discrepancies are due to minor reflection of acoustic signals related to shaft and
stringers inside the rudder and due to signal filtering

25. Conclusion
 The effects of ultrasonically induced cavitation erosion
on common shipbuilding materials were examined
both in quantitative and qualitative terms
 Good correlation between mass loss measurements
and fractographic observations was achieved.
 Cavitation stress thresholds relating to erosion were
established
 Cavitation source location method developed
 Acoustic emissions can be used for erosion monitoring
both in terms of location and intensity in ship rudders

26. REFERENCE:
 “Cavitation erosion fracture mechanisms and their
detection in ship operation ”. Fifth International
Symposium on Marine Propulsors , smp’17, Espoo,
Finland.
 “A Qualitative Study on the Relationship Between
Cavitation Structure and Erosion Region around a
3D Twisted Hydrofoil by Painting Method ”. Fifth
International Symposium on Marine Propulsors , smp’17,
Espoo, Finland.