Abstract
By fitting stator vanes behind a screw propeller energy loss of rotational flow in the slip stream of the propeller can be reduced and hence the propeller efficiency can be improved. Then the stator generates thrust to propel a ship. Therefore the screw propeller with the stator behind it acts as one propulsor. We call it stator-propeller in the present paper.So far, experimental methods were used for designing stator vanes and for obtaining propulsive performances of the stator-propeller. For experiments we need scale models of the stator-propeller and the ship, and the experimental work is time-consuming and expensive.The aims of the present research are to develop a method for theoretical calculation of propulsive performances of the stator-propeller and to develop a method for design of the stator by theoretical calculation in case that the geometry of the installed screw propeller is known.The vortex lattice method has been employed for the above-mentioned purposes. Kerwin's roll-up model has been applied as the vortex lattice model of the screw propeller. A stator has been represented by one spanwise line vortex along with rectangular vortex rings trailing in downstream. The outside duct has been replaced by a circular vortex ring in the duct and the trailing vortex lattice cylinder in downstream.The developed methods have been applied to two example models of the stator-propeller and the calculated performances have been compared with the results of open water tests. They have shown good agreement. The results of performance calculation show an appreciable improvement in propeller efficiency in open water and additionally the load of the screw propeller has reduced due to the effect of the stator.The twisting angle of the stator vane designed by the developed method for theoretical design as for the same two examples has been also in good agreement with that of actual models designed by the conventional method based on experimental data of rotational angle of flow velocity in the race of the screw propeller. This fact concludes the completion of the theoretical design method of the stator-propeller.
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