Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec
Aerodynamic loads convergence in SI units with FSI iterations:
It. Fr Fh
1051 1045
Fr/Fh
Design shape 0 316 952 0.33 Flying shape 1 313 1077 0.29 “ 2 305 “ 3 302
0.29 0.29
The first difference between the design shape and the flying shape concerns the fullness of the sail: the sail moves downwind, the forestay bends, the leech opens and the twist changes (Figure 19). Considering what happens at the 20%, 40%, 60% and 80% heights of the sail, it can be seen in figure 20 that the flying shape is less twisted than the design shape, with smaller camber, and a camber position which moves forward.
Quantifications of these differences on sail shape are given in the following table:
20% 40% 60% 80%
11° - 14° 19° - 14° 24° - 16° 30° - 18° f/c 8 – 7 13 – 10 17 – 13 20 – 15
xf/c 39 – 38 33 – 28 35 – 26 40 – 27 i 44° - 46° 68° - 63° 79° - 70° 86° - 71°
The difference between global aerodynamic loads on the design and flying shapes is about 5% for the driving force and 10% for the heeling force. In this case, sail deformation decreases sail performances.
The main results are as follows: The
importance of RANS modelling
for
optimization studies has been emphasized due to its ability to predict aerodynamic performance trade-off of sails in relation to flow separation.
On a single sail section, it has been shown that the resolution of an optimization problem based on RANS modelling is able to determine that there is an optimal camber as found in wind-tunnel tests and sea tests and that the optimal camber obtained is in the relevant range observed.
On two interacting sail sections, it has been shown that the resolution of an optimization problem based on RANS modelling is able to determine the respective optimal camber and trim for both sail sections.
For the first time, a six parameter optimization problem has been resolved to determine the best
three-dimensional sail shape
trimming to maximize the driving force. Additional results are as follows:
A user-friendly environment to run a large number of RANS simulations and to resolve multidisciplinary optimization problems about sail flows has been developed.
A high-fidelity RANS solver with hybrid meshes has been validated for sail sections and is able to capture main flow features like separated
flows on mast and mainsail configurations [19].
A derivative free optimization algorithm based on evolutionary
strategy
Figure 19: design shape (grey) and flying shape (dark grey)
implemented in
ADONF for the search of optimal rigs for complex multi-modal rig configurations has been developed.
A loose coupling FSI loop between a RANS based aerodynamic solver and RELAX a non linear structural solver has been developed.
Figure 20: four sail cuts of the design and flying shapes 8.
CONCLUSIONS
ADONF, a new computational framework for the analysis, design and optimization of flows around sails through RANS modelling has been extended to three- dimensional flows and fluid structure interaction in collaboration
with Peter results obtained in FSI mode have been presented.
ADONF as a multidisciplinary computational framework based on RANS modelling opens new possibilities for sail flow analysis and optimization. In the future, more detailed results and validations through wind-tunnel test comparisons on three dimensional sails or rigs will be conducted.
9. ACKNOWLEDGMENT
This paper is an extended and corrected version of the following paper: Chapin V.G., de Carlan N. & Heppel P.,
“Performance Heppel Associates. First optimization of interacting sails
through fluid structure coupling”, Innov'Sail 2010, Lorient, France.
and
B-114
©2011: The Royal Institution of Naval Architects
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