A New Multidisciplinary Approach For Three-Dimensional Foil Machining

The context of this paper implies disciplines of mechanical design, machining and hydrodynamics behaviours applied to propellers. Performances of propellers are linked with their shape and their surface texture. To optimise hydrodynamics behaviours, it is demonstrated in this paper that required polishing operation is not essential. To study the influence of an predefined surface texture on the performances of a three-dimensional foil, a comparative analysis is conducted. The presented methodology allows the definition of tool paths, according to the desired surface texture and upstream flow. Three foils are machined, and their performances are compared to each other: the first, considered as the reference, has a surface roughness like mirror, the second features machined peaks parallel to the upstream flow and the third has machined peaks following streamlines obtained by Computational Fluid Dynamics for operating conditions. The validation of this method is experimental: on the one hand by the manufacturing of foils following pre-established trajectories, and on the other hand by the functional test in hydrodynamic tunnel. This paper presents the methodology steps, and the hydrodynamic behaviours that the three different foils show. In a first approach, the different surface textures do not influence the lift coefficient but strongly influence the drag coefficient of a foil. Furthermore several hypotheses educed from the observed tendencies are discussed.