Hydroelastic Tailoring of Composite Naval Propulsors

Recently, there is an increased interest to use composites as alternative materials for naval structures. In addition to the important advantage of weight reduction, the deformation of the structure can be tailored to improve the hydrodynamic and/or elastodynamic performance. For naval propulsors in particular, hydroelastic tailoring can help to reduce load variations, delay cavitation inception, and improve propeller efficiency by allowing each blade to automatically adjust its shape with the local inflow. In this work, a coupled boundary element method (BEM)-finite element method (FEM) is presented for the hydroelastic analysis of flexible composite propellers in wake inflow. An overview of the formulation for both the fluid and solid domains, and the fluid-structure interaction algorithms are presented. Experimental validation studies are shown for two 0.6096 m (24 inch) model-scale composite propellers: a flexible composite propeller and a rigid composite propeller. The deformed shape of the flexible composite propeller was designed to match the rigid propeller so both propellers yield the same thrust and efficiency under the design condition. The propellers were manufactured by A.I.R. Fertigung-Technologie GmbH and designed in cooperation with the Naval Surface Warfare Center Carderock Division (NSWCCD). The experimental studies were conducted by NSWCCD. The numerical predictions compared well with experimental measurements. Additional numerical results were also shown for a different rigid and flexible composite propeller pair using the same strategy. Both steady (open water flow) and unsteady (wake inflow) results show that the flexible composite propeller achieved higher efficiency than the rigid propeller at off-design conditions by tailored load-dependent deformations that changes with the local inflow. Moreover, the enhancement in propeller efficiency due to load-dependent deformations increases when the operating condition is moved further away from the design condition for both open water inflow and wake inflow.