Question

The figure depicts the cavitation pattern of a propeller.

 

Which ONE of the following options CORRECTLY gives the description for the labels P, Q, R, S, respectively in the figure?

• A. Face cavitation, Bubble cavitation, Back cavitation, Tip cavitation
• B. Back cavitation, Bubble cavitation, Face cavitation, Tip cavitation
• C. Bubble cavitation, Face cavitation, Tip cavitation, Back cavitation
• D. Tip cavitation, Face cavitation, Bubble cavitation, Back cavitation

Hint:

Match each curve's position, low J, wide flat base, high J, or next to the back boundary, to where that cavitation type actually starts on the blade.

Answer 1

The Correct Option is B

A propeller cavitation bucket diagram plots the cavitation number against the advance coefficient. It traces a separate limit curve for each way cavitation can start on the blade, so reading it means matching each curve's position to the loading condition that produces that cavitation type.

1. P: this curve sits furthest left, at the lowest advance coefficient, where the blade is most heavily loaded and the suction side sees the largest pressure drop. That is the classic condition for back cavitation.
2. Q: this curve is the wide, nearly flat base of the bucket at the smallest cavitation numbers, spanning the normal working range. That is where bubble cavitation on the mid chord region is the limiting factor.
3. R: this curve is on the right side of the bucket, appearing again as the advance coefficient grows large and the angle of attack turns slightly negative. That lets the pressure (face) side of the blade cavitate.
4. S: this curve runs just next to P, close to the back cavitation limit but separate from it. It represents the tip vortex forming as flow rolls off the blade tip.

Matching P, Q, R, S to back, bubble, face and tip cavitation in that order gives option B.