Practical approach to unsteady problems of propellers

Abstract

Blade stress, vibratory forces and cavitation of marine propellers are treated essentially as unsteady problems arising from non-uniform wake distribution. Since a purely theoretical approach to them requires a complicated calculation based on the unsteady lifting surface theory, a simple and shorter method is more convenient for practical pruposes, if applicable with reasonable accuracy. In this regard the applicability of a quasi-steady method has been examined and the result is summarized as follows. 1. Analysis of the numerical data of unsteady lifting surface calculations indicates that a quasi-steady method may be applied to most cases in practice except for wake variations with very high frequency and extraordinary blade shapes. 2. The theoretical consideration stated above has been supported by measurements of stress at the root of propeller blades in non-uniform flow. It is suggested that the applicability of the quasi-steady method is extended to estimation of thrust and torque fluctuation of propellers working in non-uniform wake distributions.