Trans RINA, Vol 156, Part B2, Intl J Small Craft Tech, Jul-Dec 2014
Table 1: Overall wind tunnel characteristics. Politecnico di Milano Wind Tunnel – CIRIVE Tunnel Overall Dimensions:
Maximum Power (Fans only): Test
Section
Boundary Layer Low
Size
m 14 4
Turbulence 44
ms 16 55
50 15 15 m 1. 5 MW
Max Speed
UU % Turb. Int. u%
I 3 0.2 2.0 0.10
The upper leg of the loop hosts the Boundary Layer Test Section (section 14[m] x 4[m], max wind velocity: 16[m/s], turbulence intensity <2%). The 35[m] long constant section test room enables the setting up of upstream active or passive turbulence generators to simulate the atmospheric boundary layer (turbulence intensity >25%).
The model to be tested, together with the related environment,
is set up on a 13[m] diameter turntable,
included in the wind tunnel floor to permit computer pre- selected wind incidence angle change.
The high-speed low turbulence test section, the lower leg of the loop, is 4[m] wide, 3.84[m] high, and 6[m] long. It is possible to perform tests in a closed test section and in an open jet. The maximum wind velocity is 55[m/s] and the turbulence level is less than
0.1%. There are two
interchangeable closed test sections; it is thus possible to prepare a new experiment while the wind tunnel is running. Both closed test sections are equipped with a turntable (diameter
model's location, suitable for making wake measurements. There are several model supports equipped with
and mega-yacht application tests are
performed in the low speed Boundary Layer test section taking into
account atmospheric turbulent
characteristics as better described below. 2.2
WIND CHARACTERISTICS
As well known the atmospheric wind properties are a function of the environmental characteristics at full- scale: in the wind tunnel they can be achieved by using passive turbulence generators placed into the test section (typically spires and roughness elements) Figure 2.
The measured mean wind velocity and the wind turbulence intensity
vertical profiles are shown in Figure 3 in
comparison with the reference profiles relevant to marine areas according to the Eurocode specs. The flow characteristics measurements have been done in the upwind position with respect to the centre of the turntable which is the location of the model being tested.
With reference to the flow characteristics measurement uncertainty, in Table 2 the accuracy data of the probe used in the present case are reported.
2.5[m]) and a traversing system behind the a
positioning system in order to vary the incidence angle. Maxi
generally flow
Figure 2: Turbulence generators in the boundary layer test section.
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 0
V/Vrir EC0 1/30 Exp data V/Vrif SF
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0.5 V/Vrif (-) 1 1.5 0 0 10 Iu (%)
Figure 3: Mean wind velocity and turbulence intensity vertical profile. Turbulent flow & smooth flow (SF).
Table 2: Series 100 Cobra Probe Performance Accuracy (typical at most flow angles)
Flow Velocity
Flow angles
2-100 m/s ± 45° cone
Velocity Flow angles ± 0.3 m/s ±1.0°
2.3 YACHT SCALE MODEL SET-UP Given the considerable
dimensions of 20
Iu EC0 1/30 Exp data Iu SF
Wind tunnel tests are generally carried out in smooth flow first and then repeated in turbulent flow considering scaled simulation of the natural wind characteristic of the site according with turbulence and boundary layer similitude law.
30
the Milan
Polytechnic wind tunnel, the optimal scale for yacht models is in the order of 1:20 – 1:30. These dimensions derive from a series of considerations, including reducing blockage as far as possible (normally less than 5%) while at the same time it is possible to reproduce with a good level of detail many of the elements of the boat that are useful for determining superstructure drag or windage effects. This geometric scale is also compatible with the scaled simulation of the boundary layer.
© 2014: The Royal Institution of Naval Architects B-73
z model scale (m)
z model scale (m)
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