Cavitation is a phenomenon that occurs on the surface of the engine screws and rudder when the local flow velocities over these surfaces become extreme. This causes very low local pressure, which in turn vaporizes the water, resulting in:
- Damage to the screws or rudder blade due to high energy collapse on their surfaces;
- Hull vibration due to pressure variation caused by collapsing bubbles of water vapor;
- Noise emissions.
IPT analyses the geometry of propulsion screws to optimize the screw design.
In addition to standard tests to determine the characteristics of propellers in open waters, special investigations to detect pulses and noise due to pressure induced on the propeller are performed in the Cavitation Tunnel.
Very large-sized screws can be modeled and tested at high Reynolds numbers to study and prevent the phenomenon of cavitation. Observation with high-speed cameras allows for detailed analyses of hydrodynamic flows and investigation of solutions to optimize propeller design.
Preventing the effects of cavitation in propeller and rudder design requires a high degree of experience and care. Even when sophisticated numerical tools are employed to analyze these effects, the final approval of a propeller or rudder design requires a careful program of testing with scale models.
Figure caption: Study of cavitation with a propulsion model in the Cavitation Tunnel at IPT