Trans RINA, Vol 152, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun
The presence of a hull in the simulation tended to increase by 2% the magnitude of the maximum axial velocity at the extrados, the outer surface, of the jib. In the same way, the hull decreased the magnitude of the backwind in
the windward separation bubble of the
mainsail. This would mean that, at mid-span of the mast, the presence of a hull shifts the flow so that the angle of attack of the jib is increased.
When the sails and mast are solely modelled, the four vortices are clearly separated, as seen from figure 7(a). However, the presence of a hull tends to tangle the two vortices generated by the foot of each sail, as in figure 7(b). In terms of pressure magnitude, this wrapping together of the vortices in the lower part of the wake leads to a reduction by 20% in the magnitude of suction in the vortex core. Similar results were found with the Large Main rig.
(a)
(a) (b)
(c)
Figure 6: Velocity field of the non-dimensional axial velocity at mid-span of the mast for: (a) Large Main’ without hull, (b) Large Main without hull rotated by +5°, and (c) Small Main without hull
4.3 PRESSURE FIELD IN THE WAKE 4.4 SCALING EFFECTS
The pressure distributions presented in figure 7 were obtained in a transverse plane located one boat length behind the model. It appears from figure 7(a) that in this plane,
the wake consists respectively generated by:
• The foot of the mainsail • The foot of the jib • The head of the mainsail • The head of the jib
©2010: The Royal Institution of Naval Architects of four distinct vortices
The simulations so far discussed were set-up to replicate the conditions of the experiments. In particular, the scale (1:15) of the model was maintained as well as the wind- speed (4.15m.s-1). For this last part of the work, the Small Main rig, mast and hull were scaled up to full scale while the wind-speed was given a realistic magnitude of 15 knots (7.72m.s-1). The lift and drag coefficients shown in table 2 highlight that at model scale in 4.15m.s-1, the lift and drag coefficients are respectively 12% and 14%
(b)
Figure 7: Streamlines and pressure distribution in the wake for: (a) ‘Small Main’ without hull and (b) ‘Small Main’ with hull
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