Methods for Constrained Optimisation of Propellers

Licentiate thesis, 2012

Global market development, increasing environmental concerns and incessant rising fuel prices demand for high-grade efficient propulsion systems. This puts high pressure on the propeller designer to develop well-engineered and customized propeller design in a short timeframe. The design under development is always unique and requires individual consideration on several constraints. The objective of this research project is to improve the academic state-of-the-art in automatic propeller design optimisation in terms of several design constraints and optimisation procedures. The first part of the work, presented in this thesis, contains the further development of cavitation constraints that can be achieved by low-fidelity numerical methods, e.g. potential methods like vortex lattice method (VLM). Attempts were made to recognize and constrain certain types of cavities, based on sheet cavity prediction like primary cavities that tend to evolve to erosive cavitation, rather than the total amount of cavitation. Automated optimisations of the blade geometry were carried out, utilizing a combination of a Reynolds-Averaged Navier-Stokes (RANS) solver and a VLM based propeller analysis code, in a multi-objective setup, incorporating this concept and allow for harmless cavitation. A second part addresses the improvements of computational costs in automated optimisation approaches. Several response surface methodologies (RSM) were investigated to exclusively determine the propeller performance, including constraints, in a multi-objective optimisation.