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6 Experimental methodology
6.1 Dyes
The dye was injected using electric micro-pumps provided by UWAL. Dyes were “Lucky” brand
concentrated food colouring supplied by UWAL. The dye was sourced from a 1 liter container on the
input side of the pump and the dye flow was started/interrupted using a hose clamp on the output side.
The 1.2 mm inner diameter stainless steel dye probe lines were connected to the dye source using an
assortment of flexible hoses that were slipped on and off the dye probes as necessary. For the tests
where probes B1-B5 were alternately fired, aquarium air-line gang valves were used to redirect the dye
to the individual probes.
In a single day of testing it was unusual to use more than 1 litre of each of the red and blue food
coloring dyes when only flushing tests were being performed. The dyes were diluted in ratios near
50:1 to obtain a good balance between visibility and minimal use of the dye which would eventually
cloud up the water. Change-out of the water was performed on a daily basis and required
approximately 1.5-2 hours to complete. It was found necessary to flush the tunnel and then
immediately refill it in order to avoid getting air trapped in the plastic straws that make up the flow
straightener. The trapped air in the flow straightener results in small bubbles being entrained in the
flow which significantly reduces the transparency of the water. The only solution when this happens is
to flush out the straws using a hose. However, this results in large amounts of trapped sediment being
flushed from the straws, which (at least in our one attempt at this procedure) muddies the water beyond
usability for testing.
Tests requiring relatively small amounts of dye (i.e. flushing time tests) were generally performed early
in the day when the water was still clear. Flow visualization tests requiring continuous dye input over
several seconds were performed at the end of the day when the dye had significantly clouded the water.
The red and blue dyes were selected based on their better contrast in the water as suggested by Robert
Gordon, with red being more visible than blue.
The method used for initiating the dye injection was to first turn on the micro-pumps, wait a few
seconds for the output pressure to build up and then simultaneously open the hose clamps to begin the
dye injection (this was generally controlled by Karun). In this way, if more than one dye color was
used, the dyes would be injected simultaneously to within a few 100 ms. It is important to note this as
some of the video footage appears to indicate that the blue and red dyes (e.g. for the A3 & A5 probe
flushing time tests) enter the chamber at very different times. This is an illusion caused by the strong
flow along the dome floor in certain slit to wind orientations compounded by the mezzanine blocking
the camera's view of the dome floor.
6.2 Lighting
The model was lit from one side with three 500 W halogen light fixtures. Two of the light fixtures
were placed approximately 50 cm above floor level (~35 cm below the bottom of the tank) while the
third fixture (a spot light) was at tank level aimed towards the downstream tank direction. With this
arrangement, reflections were avoided from the vantage point of the cameras. However, some
shadowing is visible due to partial blocking of the spot light by the storyboard (this is particularly
evident in the bottom camera views).
A white fluorescent light panel (part of the UWAL water tunnel setup) was placed on the side of the
tunnel opposite the “side-view” camera.