Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec 7.5 7.5.1
PRELIMINARY FSI RESULTS FSI Analysis
As a first FSI analysis, we are considering the flow around a genoa alone in upwind conditions. This genoa design is taken first to quantify the influence of the aerodynamic model on the resultant flying sail shape and the influence of the structural model on the aerodynamic loads for two apparent wind angles (30°, 33°).
Figure 12 gives a comparison of three sail shapes: the design shape in grey, the flying shape given by RELAX with a constant pressure distribution resulting in the same aerodynamic force and the flying shape given by RELAX with a pressure field obtained by a three- dimensional RANS calculation. Regions of differences may be observed. The luff and leech regions are important
regions of differences with a high
dependence of the sail entry angle to the tension of the forestay. This will be seen in more details in the next section.
Figures 13 and 14 give a comparison of the friction lines along leeward genoa surface for two apparent wind angles (30°, 33°) on the design shape and on RANS flying shape.
Figure 13, shows that the flow doesn’t separate on the leeward side of the sail for the lower apparent wind angle but it may be observed that separation is not far away. Always in Figure 13, at the higher apparent wind angle, separation takes place on the lower part of the sail. For RANS converged flying shapes, it is seen in Figure 14,
that
the flow separates for both apparent
wind angles. Separation is present only in the middle part for the lower apparent wind angle. Extension of the separation region is far larger for the higher apparent wind angle. This last case is nearly totally separated on the leeward side of the genoa.
The separation extension on the sail surface has an impact on driving and heeling forces. On design shapes, the driving force increases by 10% when the apparent wind angle increases by 3° despite the separation which takes place on 20% of the sail surface. On flying shapes, the driving force is decreased by 20% when the apparent wind angle is increased by 3° because of the total three-dimensional separation on the leeward side of the genoa. These four visualizations of the leeward side of the genoa clearly illustrate
the relative
importance of aerodynamic and structural effects that may take place on sails.
Figure 15 shows friction lines on the windward side of the genoa for both apparent wind angles on the flying shapes calculated by RANS-FSI. This sail side is simpler to analyse with no strong non linear phenomena except on the bottom part of the genoa with the tip vortex (Figure 16) and the top part with a high vertical velocity component
along the stay which is more
pronounced on the head part of the sail. This vertical component is very high for the highest apparent wind angle with a totally separated flow on the leeward side (Figure 15).
It will be interesting to observe these flow fields on the genoa in the interaction with a mainsail to have a finer understanding of the interaction consequences on the three-dimensional flow fields.
All these figures clearly show the interest of three- dimensional FSI simulations. With these detailed flow fields, it becomes possible understanding of
to increase our
Figure 12: design shape (grey), flying shape / RANS (white), flying shape / uniform pressure (black), (left) leeward side (right) windward side (bottom) top view
on aerodynamic forces three-dimensional viscous flows, to
observe the emergence of separated regions with design parameters variations and to quantify their consequences performances.
and sail global
B-112
©2011: The Royal Institution of Naval Architects
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62