1 Overview 2 Details of the Model Construction - Canada France ...

gradually narrows down over a length of ~4-5 m to the dimensions of the test section. A smaller pump
continuously filters the water in the tunnel. At night, we normally left the water tunnel running at a
slow speed (~5 cm/s), with the filter pump on to help clarify the water and reduce bubbles due to
entrained air. A large valve is provided on one side of the tunnel for draining out the water. The
capacity of the water tunnel is ~5000 gallons, and it is filled directly from the mains through a 1” pipe.
Other than the chlorine in the water supply, no additional bleach nor pH modifiers were used.
The exact width of the test channel is 75.2 cm (29-5/8”) and was operated at a depth of 62 cm as
measured approximately 80 cm from the model in the upstream direction. At this depth the free-stream
water speed in cm/s is determined by multiplying the variable frequency pump drive frequency by
1.013 and adding the correction -0.224 cm/s. Thus at the selected operating frequency of 30 Hz that
was used for most of the testing, the nominal free-speed water speed was 30.2 cm/s. For simplicity, in
the following we rounded-off the water speed to the nearest cm/s, which is equivalent to the nominal
pump frequency used with Hz units directly exchanged for cm/s.At the nominal speed of 30 cm/s, with
water temperature at 5°C, the Reynolds number is 4x10 4 , using the dome diameter as the characteristic
length.
Figure 12: The observatory model installed in the University of Washington water tunnel facility. Note
the two storyboards (to the left and above the model) used for noting the experimental conditions. The
“side view” video camera was located immediately to the left of the vantage point seen here, centered
on the model and perpendicular to the tank wall.