Deliverable D21.11 - Results of model tests on optimised configurations

Results of experimental work to evaluate design solutions aimed at improving the hydrodynamic performance of state-of-art screw propeller systems are presented. The report is written in fulfilment of the STREAMLINE Project Deliverable D21.11 `Results of model tests on optimised configurations.\u27 The work documented herein is performed in the framework of Work Package 21, Task 21.6 in which propulsion efficiency enhancements deriving from the application of CFD- based design and numerical optimisation tools are investigated. Results of CFD-based design and optimization studies carried out in WP21 Tasks 21.2 to 21.5 determine new hullforms, propellers, rudders and inflow-improving devices to update the STREAMLINE WP21 Tanker, a 7000 DWT ship design taken as representative of an important class of merchant vessels. Specifically, the following new layouts determined from CFD studies have been the subject of model test verification: 1) an optimised hull aftbody and corresponding propeller 2) a propeller optimised for the original hullform 3) an optimised propeller/rudder layout based on the twisted-rudder concept 4) three alternative inflow improving devices Layout no. 1 may be considered as a new ship design, whereas layouts 2 to 4 provide examples of retro-fit studies. The hydrodynamic performance of the new configurations is analysed through model tests and results are documented in the report. Experimental work has been performed at CTO Towing Tank and at CNR-INSEAN Towing Tank and Circulating Water Channel. A comprehensive test matrix has been shared between the two organizations to provide results for ship resistance and propulsion, nominal wake measurements, propeller open water performance and induced pressure pulses under both non-cavitating and cavitating flow conditions. The emphasis in the present report is on the analysis of results of model tests whereas the comparison between model test results with performance predictions obtained by computational models at design stage is the subject of a separate STREAMLINE Project Deliverable. The analysis of model test results allows to draw the following main conclusions for each of the design modifications addressed. Results of model tests and extrapolation to full scale provide a clear picture of the range of hydrodynamic performance improvements that is possible to achieve through advanced CFD-based design and optimisation. Specifically, a totally new hull aftbody design can determine improvements of hydrodynamic performance that in the case of the STREAMLINE tanker are of about 8% for the delivered power. Part of this improvement is due to modified hull lines that allow to fit a 7% larger diameter propeller. If a new hull aftbody represents a major deviation from the original design and large performance variations are expected, efficiency gains can be also obtained with a limited cost through retrofitting studies. This is the case of replacing the original screw with a new propeller from a shape optimization study. The case addressed here presents a new propeller with an increased open water efficiency of more than 3%. Twisted-rudders and inflow devices determine very limited power reductions in the range of 1% (pre-swirl stators) or 1-4% more power in other cases. Nevertheless the capability to modify the inflow to the propeller is demonstrated from results of velocimetry measurements. Device type and layout can be designed to obtain sensible improvements of the qaulity of the inflow to the propeller with corresponding lower pressure pulses and vibratory loads