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Experimental
With
the fan turned off, open the wind tunnel WITH CARE and place
the selected test device in the fixture attached to the force balance. Make
sure that it is well secured to the fixture (otherwise it may convect down the
tunnel at high wind speeds). If a wheel is chosen, the wheel rotation using
the drive motor. Adjust the orientation of the fixture so that the wheel is
parallel to the sides of the tunnel. Set the lift and drag potentiometers so
that their associated scales read zero with the wheel static in the fixture.
Rotate the wheel over the expected angular velocity range (still with the tunnel
open) and see if the lift and drag readings depart from zero. Select a
maximum angular velocity of the wheel to correspond to a road speed of about
8 m/s. When you are sure that the wheel is properly mounted, stop it rotating
and shut the tunnel door. Before starting the tunnel make sure that the cooling
water is turned on.
Make measurements of lift and drag on the selected
test device. Start at low air speeds and allow the
system to stabilize
at each value. Take several readings and obtain a mean value for lift and
drag at the
selected wind speeds. When making measurements on a wheel, repeat
these readings with the wheel rotating at several angular velocities. Set
a rotational velocity and increase the air speed over the wheel measuring lift
and drag as before. Repeat this for two more wheel rotational speeds.
The
angle between the test device plane and the wind direction should now
be altered and the above
measurements repeated. A reasonable maximum angle
is 150. Test the shape at the same angle with
respect to the
air flow on either side of the tunnel axis. If two wheels are being compared,
repeat this sequence of measurements with the other wheel. |
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