Evaluation of Novel Wingsail Concepts in Terms of Aerodynamic Efficiency
Examensarbete för masterexamen
Engineering mathematics and computational science (MPENM), MSc
In this project the evaluation and comparison of five different designs for rigid wingsails were made by performing simulations in the CFD software STAR-CCM+ and two parameters, gap distance between foils and camber angle for three of the wingsails were varied to understand its effects. The wingsails in question were the crescent-shaped profile, two-element foil sails and three element foil sails. Three different designs were created for the two element foil sails with the following ratios of the total chord length between the front and aft foils; 70/30, 80/20, 90/10, and only one design for the three element foil sail with ratio 15/70/15. The parameters of gap distance and camber angle were only altered for the two element foil wingsails, while only the camber was altered for the three element foil wingsail. The comparisons that were made between the different designs were between the propulsive performances as well as stall angles. This study has found that, regarding the two element foil designs, the absence of a gap between the front and aft foils yield superior propulsive performance and that the difference in performance between different non-zero gap sizes is not very significant. The crescent-shaped profile performs significantly better than the non-cambered multi-element foil sails, but appeared to be a less favourable design when compared with the no-gap, cambered multi-element foil sails. However 3D simulation results revealed that the performance of the best multi-element foil design, the two element foil sail with ratio 70/30, no gap and 25° camber had been severely overestimated, and performed worse through all apparent wind angles when compared to the crescent-shaped profile. If we were to assume that the relation between the multi-element foil designs remained the same, in terms of performance over all apparent wind angles, when performing 3D simulations, then they would be ranked as follows. The best designs in terms of overall propulsion, in order of greatest to worst, are the crescent-shaped profile followed by the two element foil sails with ratio 70/30 and 80/20 with no gap and 25° camber and lastly ratio 90/10 (also no gap and 25° camber) and the three element foil profile with ratio 15/70/15 and 15° camber. It was discovered that the crescent-shaped profile began to experience stall, often much later than the multi-element foil designs, and reached its critical angle of attack earlier as well.
Rigid wingsail , Stall , Camber , Crescent-shaped profile