2.1. The Wind tunnel
The rapid scanning tests were carried out in the 2 meter Wind Tunnel (2mWT), a low speed wind tunnel at the Defence, Peace, Safety and Security (DPSS) Operative Unit of the South Africa Council for Scientific and Industrial Research (CSIR) in Pretoria (RSA). In Fig. 2.1 is reported a sketch of the 2mWT.
2500 mm
1700mm 2000 mm
Uinf x y z
Wing Model
g
Figure 2.1. Sketch of the wind tunnel and frame of reference.
The speed range of the wind tunnel is between 3 and 33 m/s. The open test section has a length of 2500 mm. Further dimensions are depicted in Fig. 2.1. The flow is generated by a drive system equipped with 30 kW power electric motor and velocity is set by a dedicated control panel. The free-stream turbulence level is about 0.75 % and the pressure gradient along the tunnel axis (dCdxp) is −0.9 % m−1. The 2mWT is equipped with a vortex generator, shown in Fig. 2.2, in order to reduce vibrations generated from the diffuser (see [6] and [23]).
Figure 2.2. 2mWT vortex generator.
Maintaining the same convention of [6], [23] and [2] the frame of reference was defined as follows:
• origin at the tip of the wing model;
• x axis as the free-stream direction;
• y axis as the spanwise direction of the model from the root to the tip of the wing;
• z axis was consequently defined, producing a clockwise frame of reference.
The reference system is depicted in Fig. 2.1.
The facilities used in the 2mWT include the basic instrumentations to measure static and dynamic pressure and static temperature. The instruments characteris- tics are reported below:
Dynamic pressure transducer
Model: 239
Range: 0 to 0.1 PSI Output: 0 to 5 Volts DC
Static pressure transducer Brand: Huba Control Model: 15T80
Range: 800 to 1200 mbar P abs max 2 bar Output: 4 to 20 mA
Temperature probe
Brand: Wika Instruments LTD Model: 10-1100
Range: 0 to 100 ◦C Output: 0 to 10 Volts DC
All wirings to connect the transducers with the acquisition system and to the power supply units were executed and a preliminary check to verify all instruments was performed. The pressure transducers were calibrated using the procedure explained in Sec. 3.1.1.
The 2mWT has not a permanent traversing apparatus. The movement rig, used for previous works (see [6], [23] and [2]), and adapted for the present campaign, is equipped by three stepper motors that allows displacements along the x, y and z axes of the tunnel frame of reference. The traversing apparatus is controlled in remote.
The data acquisition used is NI PXI 6052E, and its characteristics are summa- rized in Tab. 2.1.
Analog inputs 16 SE/8 DI
Input Resolution 16 bits
Max Sampling Rate 333kS/s
Input Range ±0.05 to ±10V
Output Rate 333kS/s
Output Range ±10V
Digital I/O 8
Table 2.1. Specifications of the DAQ NI PXI 6052E.
2.1.1. The model
The model used for the present experimental campaign was an unswept half wing with constant cross-sections NACA 0012 and bluff tip. No boundary layer trips were applied on the wing model during tests. Its geometrical characteristics were:
Wing semi-span (b/2): 700 mm Mean geometric chord (c): 245 mm Mean aerodynamical chord (c∗): 260 mm Root chord (cr): 350 mm
Tip chord (ct): 140 mm Taper ratio (λ): 0.4 Aspect ratio (AR): 5.7
Projected surface (S): 171500 mm2
minium splitter plates from both sides. A sketch of this set-up is reported in Fig. 2.3.
Half W
ing Model
Base Plate
Splitter Plates
Figure 2.3. Half wing model positioning.
The whole base was fixed to a support which allows to set the angle of attack of the wing by a manual rotating gear. The structure was designed in order to place the wing tip at the centre of the test section. Once the model was positioned, the horizontality of the base plate was checked with an inclinometer and the verticality of the wing was controlled using a theodolite.
