Ring thruster – a preliminary optimisation study

Abstract

The ring thruster is a new type of propeller, for which there is no experimental data to verify analytical design calculations. A significant feature of the ring thruster is the absence of a shaft. Propeller blades are mounted to the ring rotating inside the housing, which has the shape of a nozzle. For this reason the ring thruster is closest, with respect to both the construction and principle of operation, to the Kort nozzle propeller. The absence of a shaft and no gap between the blades and the nozzle make it impossible to fully relay on results obtained from Kort nozzle propeller examination. What is more, the already existing computer codes developed for designing Kort nozzle propellers cannot be directly used for designing ring thrusters either. That is why for this purpose a new code determining hydrodynamic characteristics based on the theory of the vortex lifting surface will be used. When using the above method, some differences between calculated and experimentally recorded results are expected to be observed. To a significant extent, the level of the torque taken by the thruster will be affected by drag of the rotating ring to which the blades are fixed. Examining a propeller equipped with a rotating ring has revealed that the expected torque increment may reach as much as a few per cent, at the comparable level of axial force (thrust). At the present stage of ring propeller investigations there is no data available on how to shape the ring propeller blades. Possible comparison calculations, done using the existing computer code, will allow, the most, the shape of the blades to be determined for preliminary tests in the cavitation tunnel and on a self-propelled model. And only the results obtained in these tests will provide opportunities for verification of preliminary design calculations. It should be stressed, however, that developing design procedures for this type of propellers will require additional optimisation calculations, with further experimental verification. And this should be the subject of separate investigations.