Abstract
The former experiments have revealed that the ventilation mode can be classified into the partial ventilation characterized by the unstable air cavity and the full ventilation characterized by the very stable sheet cavity formed over the whole blade, and as for the vibratory shaft force, revealed that (i) the shaft forces are induced only by the partial ventilation region, (ii) the shaft force becomes very large in a certain range of experimental conditions. In the former experiments, however, the dynamic interaction between the free surface and the ventilation phenomenon could not be observed in detail. So the following experiments were carried out by the use of the newly improved measuring apparatus. It has been made clear that (i) the main frequency component of the shaft force due to the ventilation is equal to the shaft revolution rate, (ii) the strong interaction between the free surface and the ventilation occurs in a certain range of the partial ventilation region, and induces the very violent shaft forces.
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