Curved fibre path optimisation for improved shape adaptive composite propeller blade design

The propulsive efficiency of a shape adaptive composite propeller increases with passive pitch (twist) change under a hydrodynamic load. These adaptive marine propellers are usually designed using straight fibre tows to obtain optimised layup with such bend-twist character. This paper aims to present an alternative optimisation approach for such composite propellers using a curved fibre path method where tow paths are allowed to vary spatially within individual plies. In this work, three optimisation studies were performed to highlight that employing curved tows produce better results, including increased twist change for efficiency or, lowered deflection for structural improvements. Laminate plates were first optimised and manufactured using an automated fibre placement robot for experimental validation. Cantilevered loading test results show that optimised curved fibre plates generated > 10% more twist compared to their straight fibre counterparts. In the following optimisation on a hydrofoil model, the curved fibre design produced the same tip angle change as the optimised straight fibre layup, yet it reduced the tip deflection by 15%. Finally, the optimisation was performed on a Wageningen B-series marine propeller, in which the optimised blade design with curved fibre layup achieved a 20% reduction in the Tsai-Hill failure index under the same pitch change.