The evolution in nature has developed a huge amount of solutions, very often favouring those with better energy efficiency. Flying birds especially show interesting solutions to minimize the induced drag loss of their wings. Analyzing the principles behind means following the bionics approach of understanding and transferring them into a technical application. The loss due to the tip vortex, being inevitable, can thus be reduced by splitting the vortex. Therefore bird wings utilize splitted primary feathers. A technical adoption of this principle is the winglet. The bionic propeller represents an attempt to gracefully apply this principle to propeller blades. Common design procedures are almost overburdened with the complex topology and inner dependencies of the bionic propeller, even to depict an optimum design configuration. Nevertheless an inverse approach is possible by using a cyclic optimization process, where beside the proper optimization strategy only an evaluation of the probe quality is necessary to provide. Here the evolutionary strategy comes into play, proven to be superior appropriate for complex optimization targets, even if these can be treated as black boxes. In realization of this approach an optimization environment has been developed, based on CFD evaluation of the probe quality. Verified to sufficiently perform with the conventional propeller topology, the environment was extended to deal with the more complex one of the bionic propeller. It turns out that the optimization process slowed down, the CFD computation became even more complicated. To keep track on the goal an additional quality evaluation function was established based on the vortex lattice method. This procedure is in fact less accurate, but on the other hand it computes considerably faster than RANSE-CFD. With both evaluation functions and with permanent alignment of the variants with the project partner SVA-Potsdam, numerous promising configurations have been made up, many of them evaluated for their open water characteristics both by RANSE-CFD methods and by real measurement. The most promising variant have been selected and prepared for full-scale manufacturing, which was finally performed by project partner MMG Waren. The real life test under productive operation conditions revealed - as expected - an advantage of the bionic propeller at high thrust loading coefficients. No critical cavitation erosion have been observed for 8 weeks of operation. The propeller has yielded a considerably lower noise level. Finally the mission operation was limited after all only by the mechanical sensitivity of the loops.
|School:||Technische Universitaet Berlin (Germany)|
|Source:||DAI-C 81/1(E), Dissertation Abstracts International|
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