Wärtsilä and City University London have jointly undertaken a research project to detect the specific design parameters creating the risk of ‘singing’ propellers of a ship.
The phenomenon ‘singing’ is a sharp tonal noise emanated from the propellers which hinders the onboard comfort level.
Before the recent revelation, the cause behind the phenomenon was attributed to the coinciding of the frequencies of propeller blades’ vibration mode with the the hydrodynamic excitation forces at the trailing edge of the blades.
Wärtsilä Marine Solutions propulsion vice-president Arto Lehtinen said: "Our research has shown that the ‘singing’ phenomenon can be controlled by selecting the proper main parameters of the propeller blades, by careful attention to the flexural modes of the propeller blades, and by careful attention to the specific geometry at the trailing edge of the blades.
"It has shown that all these aspects are interacting and can prevent the ‘singing’ of propellers."
The research programme had leveraged on the finite element method (FEM) analysis tools to detect the risk indicators related to the main propeller design parameters.
The FEM is a 3D model used to import the design of a ship to analyse, which involves simulation of the operation of the machinery.
It was determined that the noise feedback generated from the indicators can be mitigated by adjusting the design paramemters.
On a similar note, computational fluid dynamic (CFD) technology was used to analyse the vortex shedding behaviour of the trailing edge design.
The results highlighted the fact that a proper design imparted on the trailing edge details will minimise the shedding, as well as the excitation forces.
The process of minimising the ‘singing’ noise emanated by the propellers is now implemented across all the Wärtsilä propeller designs.
The findings of the research project have also been implemented into the company’s OPTI-Design, which accounts for fuel savings and a full scale performance prediction.
Image: Ship propellers underwater. Photo: courtesy of Wärtsilä.