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

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Figure 20: (Left) U-tube manometer for flow speed measurement, start stop button for the electric drive, and hydraulic control unit to set the pitch of the propeller blades. (Right) Power unit consisting of the variable pitch propeller driven by an electric motor (view from test section toward the exhaust end). Figure 21: (left) Telescope model mounted on the wooden trapdoor in floor of the test section prior to the flow visualization using china clay (i.e. zero windspeed). (right) View from top showing the width of the test section and the trapdoor. The flexible polythene piece upwind of the test section has a hole through which a wand with tufts,or a pitot tube may be inserted into the flow. The polythene sheet slides from side to side across the flow direction permitting probing the flow at various points (picture taken after the ‘china clay’ test). Unlike the Kirsten wind tunnel, the 36” tunnel does not have a balance or other instrumentation for force and moment measurement. Should such measurements be needed, we would have to instrument the model with load cells or similar sensors, and all the required readout electronics; UWAL provides no facility for such measurements. The bottom of the test section is ~ 3’ off the floor, so there is adequate room for wiring and instrumentation. At most, UWAL may be able to provide hand held pitot tubes for dynamic and static pressure measurement, and a smoke wand for flow visualization.
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
Page 1 and 2: Canada-France-Hawaii Telescope Corp
Page 3 and 4: Figure 3: Vent dimensions in inches
Page 5 and 6: Figure 6: View through the shutter
Page 7 and 8: 4 Dye Probe Locations Dye probe por
Page 9 and 10: gradually narrows down over a lengt
Page 11 and 12: 6.3 Video capture Two Panasonic Lum
Page 13 and 14: 4. Windscreen position (3): Either
Page 15 and 16: dye probe was held near each vent l
Page 17 and 18: 10 Lessons learned • A dome shutt
Page 19 and 20: Figure 17: Path structure used to o
Page 21: 11 University of Washington 36” W
Page 25 and 26: ing everything needed. • It takes

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