Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014 4. SOME RESULTS
In the following some exemplary results obtained with reference to aerodynamic investigations
carried out,
using a scale model of a 270’ LOA mega-yacht designed and built by Azimut-Benetti boatyard, are shown as a reference for a better consideration of aerodynamic aspects in maxi and mega-yacht design.
4.1 FORCE: AERODYNAMIC COEFFICIENTS
Figure 9 shows an example of aerodynamic loads measured at different wind exposure angles (from 0 deg to 180 deg). Results are presented in the yacht reference system (Figure coefficients.
0.2 0.4 0.6
-0.8 -0.6 -0.4 -0.2 0
Mean-CFX-Yacht-SF-8 m/s Mean-CFX-Yacht-SF-12 m/s Mean-CFY-Yacht-SF-8 m/s Mean-CFY-Yacht-SF-12 m/s Mean-CMZ-Yacht-SF-8 m/s Mean-CMZ-Yacht-SF-12 m/s
where Fi, and M are respectively the forces and moment measured by the dynamometric balance, q is the onset flow dynamic pressure, D and L are reference dimensions.
The forces defined in reference directions x and y (fixed with the structure) can be projected in the along-wind and cross-wind-direction, in an horizontal plane, in order to define
aerodynamic coefficient CL. Results of Figure 9 are relevant (8m/s – 12m/s) in
measurements repeatability. 11) in terms of non-dimensional
Finally Figure 10 shows the X force coefficient with its standard deviation related to the wind turbulence effect at various angles of exposure (from 0 [deg] to 180 [deg]).
condition; tests have been repeated at two different wind speeds
drag aerodynamic coefficient CD and lift to smooth flow order to check the
0
20
40
60
80
100 (deg)
Figure 9: X-force, Y-force and Z-moment mean coefficient as function of the angle of exposure. Two wind speeds: 8m/s and 12 m/s.
Figure 11: Yacht reference system.
4.2 SPEED UP As mentioned above comfort evaluation on the various yacht decks and living areas are performed by means of local wind speed measurements carried out in different positions according to yard and designer specifications (typically on yacht terraces and yacht decks) at different wind exposures. Figure 12 shows an example of the results obtained in turbulent flow at 0 deg wind exposure with reference to the yacht sun deck level.
Figure 10: X-force mean coefficient and standard deviation as function of the angle of exposure. Wind speeds: 8m/s Turbulent Flow (TF).
Global forces are presented through non-dimensional aerodynamic coefficients. The aerodynamic force coefficient CFi and the aerodynamic moment coefficient CM are defined according to the following equations:
CFi F qDL ix ,; y
C M qD L
M 2
The results are presented in a non-dimensional form by means of the speed-up factor.
The speed-up factor S is defined as the ratio between the local mean wind speed V in the measurement position and a reference wind velocity (Vref):
S V Vref
The reference wind velocity assumed in this case is the onset flow mean wind speed measured in the wind tunnel test section at 10m full scale height above the sea.
© 2014: The Royal Institution of Naval Architects B-77
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CFX (-), CFY (-), CMZ (-)
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