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

Note: at the expected operating wind speed of > 100 mph during our tests, smoke for flow visualization
is ineffective.
11.3 Tests performed
In the half day available for testing we ran two classes of tests, mechanical integrity and flow
visualization. The model was mounted on the wooden trapdoor without any terrain in order to keep the
blockage factor well below the 10% advised. We used only the unvented dome for all the tests. The
wind speed was maintained at 140 mph, which translates to Re ~ 10 6 using the diameter of the model
dome as the characteristic length. Compared to the Re in the water tunnel, this is more representative
of the Reynolds numbers, ~10 7 , expected in the flow around the telescope facility on Mauna Kea..
11.3.1 Mechanical integrity of the model
Our main objective was to test the mechanical integrity of the model used in the water tunnel tests
when exposed to wind speeds of 140 mph. With this information, we aimed to assess whether we could
carry out the wind tunnel tests using a similar model in this 36” wind tunnel facility, which is rarely
used and is available for the asking. This is unlike the Kirsten wind tunnel, which we were told was
booked completely for the next few months till August 2011.
The unvented dome was oriented such that the slit was at 15° to the wind direction (dome azimuth of
105°). This is the angle at which we had observed the minimum flushing times in the water tunnel tests.
The wind speed was gradually increased to the maximum of 140mph, and was sustained at this value
for a considerable time (~20min). During this period, the dome orientation was changed using the
thumb-wheel, in order to expose the dome to the full range of forces.
The dome stood up to the wind speed without any obvious distress, except for a loud whistling noise
due to the wind entering the slit at certain angles. Given this very encouraging success with Tom and
Marc’s fabricated model, it is quite feasible to carry out the wind tunnel tests using a similar model.
11.3.2 Flow visualization with tufts
The aim here was to use “tufts” to visualize the flow both outside the telescope building and inside the
dome, and thus benchmark the patterns we had observed during the water tunnel tests. Tufts are small
pieces of yarn, each ~ 1/2” to 1” long, fixed at regular intervals on the test surface, e.g. on the dome
skin using scotch tape, as in Figure 22 (left). (see Appendix 1).
For the initial tests, the tufts were affixed horizontally at equal intervals along the dome, as well as on
the building at approximately the height at which we had seen the top of the Horseshoe vortex in the
water tunnel test. In addition, we laid a few rows of tufts behind the building in order to visualize the
eddy and backwash also observed in the water tunnel. Two video cameras recorded the trials, one
filming from the North, and the other from the top looking down on the model; the directory structure
given at the end of the document lists the names of the video clips corresponding to these tests.
In addition to these fixed tufts, we also fixed two long tufts on a hand-held metal probe which we
introduced into the flow through the hole in the movable polythene sheet or from an entry hole on top
of the test section (seen in Figure 21). The tufted probe was moved methodically from side to side in
the flow as well as in the vertical direction in order to scan the flow pattern on the upwind side of the
dome thoroughly.
For the initial tests, the tufts were affixed horizontally at equal intervals along the dome, as well
as on the building at approximately the height at which we had seen the top of the Horseshoe