Flow over a Magnetically Suspended Cylinder in an Axial Free Stream

II. Experimental Set Up
A. Magnetic Model Suspension, Force Balance and Wind Tunnel
The experiment was conducted using the Magnetic Suspension and Balance System at the Institute of Space
Technology and Aeronautics, Japan Aerospace Exploration Agency (formerly the National Aerospace Laboratory). The system
was developed by the second author and is described in Ref. 4. Figure 1 shows schematically the coil arrangement used
in the system, and specifications of the individual coils are listed in Table 1. The position and attitude of the model
were monitored by two CCD cameras oriented perpendicular to each other. Two colors and filters were used to
separate reflected lights in two directions. The position was controlled at a feedback frequency of 248Hz. The magnet
current was calibrated against known force applied through pulleys and weights for each model. The calibration was
repeatable within 0.02%. The models were made of aluminum alloy and housed a rod-shaped magnet along their
centerline. The balance system was installed in the subsonic wind tunnel with a 60cmx60cm test section. The available
flow speed ranges from 10 to 35 m/s. The free stream turbulence level was less than 0.05%. The measured flow angle
at the center is 0.05 degree in downwash and 0.15 degree about z-axis shown in Fig. 1. Further detail of the MSBS and
the wind tunnel can be found in Ref. 4.
model
coil # turn number size purposes
0,9 50 620 x 620 drag
1,3,5,7 97 + 97 200 x 200 lift,
pitch moment
side force ,
yawing moment,
rolling moment
130V, 120A in continuous mode … 3 units
130V, 60A in continuous mode … 4 units
5 DOF for models with a main magnet only
6 DOF for special models with pair magnets
2,4,6,8 100 200 x 200
coil drive
units
control
Table 1 Specifications of the 60cm MSBS (Ref. 4)
position sensing camera
Fig. 1 MSBS coil arrangement (not to scale,
only one camera is shown)
B. Test Models
Figures 2 illustrates cylindrical models supported magnetically in the test section. In addition to the model edges, the
sensing cameras use a vertical stripe in the middle to detect the model position and attitude. Instantaneous model position
was monitored and held within ±0.2mm. In order to provide a wide range of the fineness ratio, models with different
diameters were used. One had 45mm diameter and shared the same center section enclosing the magnet. By changing the end
caps of different lengths, nine fineness ratios between 4.13 and 8.13 were achieved. Second set of model had a diameter of
85mm and the third 110mm. These larger diameter models provided the fineness ratio down to 1.272. An additional model of
25mm diameter and fineness ratio of 6 was also used. The Reynolds number based on the diameter ranged from 60,000 to
100,000.
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American Institute of Aeronautics and Astronautics