Hydroelastic tailoring of flexible composite propellers

Abstract

This paper describes and demonstrates a method for the hydroelastic tailoring of flexible composite marine propeller blades. This method is applicable to situations in which the propeller's shape adapts to changing flow conditions due to its rotation in a spatially varying wake, resulting in improved efficiency when compared to a rigid propeller. The unloaded shape of the flexible propeller and the composite lay-up are determined using an optimisation procedure. Design calculations for an example propeller revealed an improvement in the performance over a range of operating conditions. However, this may have been greater if, first, the geometry of the rigid propeller that was the basis of the flexible propeller was optimised so that it was more suited to take advantage of the hydroelastic tailoring, and second, composite materials were selected to maximise flexibility within the strength requirements. Also, a closed-form expression was developed for estimating the efficiency gain of a flexible propeller at the design condition in a spatially varying wake flow. The potential benefit of a flexible propeller is that it broadens the efficiency curve and reduces the sensitivity of the losses usually manifested in the spatially varying wake flow.