Numéro : 2307 - Year : 1999

About the working of the COSTA bulb

M. EBERSOLT, MERIMAR

Open water tests on schrouded propellers equipped with fixed contra rotative fins showed that this device presents a better efficiency compared with conventional ones. A set of trials were executed replacing the contrarotating device by a single fin, with or without Costa bulb. The best result is obtained with the combination fin plus bulb. Other trials executed in water tunnel points out. that the hub vortex disappeared in both cases. Examination of general arrangement of flow shows that it becomes directed and stable due to the influence of the Costa bulb. An explanation of this phenomenon is proposed, which confirms power saving and vibrations cut down.

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