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

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CFHT Dome Venting Studies: University of Washington Water and Wind Tunnel
Tests, March 2011 – Description of work performed and distributed data
Authors: Marc Baril, Tom Benedict and Karun Thanjavur
Revision date: April 14 th , 2011
1 Overview
Water tunnel tests using three models of the CFHT observatory were performed in the 30” water tunnel
at the University of Washington Aerodynamics Laboratory (UWAL) on March 7 th through March 10 th ,
2011. In addition, a half-day of testing on March 11 th was performed in the UWAL 36” wind tunnel to
verify survivability of the models used in the water tunnel when subjected to 145 mph wind speeds as
well as to provide a comparison of the general nature of the flow with what was observed in the water
tunnel.
The purpose of this document is to provide a description of the tests made rather than an interpretation
of the data which is to be treated in one or more follow-up documents. We do however provide here an
interpretation of the test performed to determine the water tunnel operating speed as this was necessary
at the beginning of testing to validate our experimental conditions.
2 Details of the Model Construction
The models consisted of three acrylic domes that could be interchanged and mounted on a single model
of the observatory building and telescope. Each dome incorporated a ring gear on its base that allowed
for easy rotation of the dome while testing (Figure 2). The diameter of the domes was 20.3 cm (8” ±
0.1”) which corresponds to a model scale of 1:160.
The observatory building was made of marine grade mahogany plywood, stacked, glued (with a
waterproof PVA adhesive) and turned on a wood lathe. The dome floor was fabricated from aluminum,
as were the mezzanine and freight elevator blocks. These latter two items were secured with machine
screws through the bottom of the model to allow interchange of the model domes.
The acrylic spheres from which the domes were cut were procured from California Quality Plastics
Inc.; the shutter apertures were cut into these spheres by the same company. The vent holes were
manually cut on the mill at CFHT by Tom Benedict. Structures on the dome such as the lip on the edge
of the shutter opening, windscreen (deployed at 50% and 100%) the existing vents on the top of the
dome and the shutter itself were produced out of ABS plastic using a 3D printer by Solid Concepts, Inc.
Steve Bauman reduced and simplified Dan Sabin's detailed 3D CAD model of the dome for this
purpose. In addition, ABS pieces representing shutters for the (proposed new) vents were produced
using the same technique so that the effect of blocking these could be investigated.
The vent placement for the small and large vent domes are shown in Figure 1 and Figure 2 respectively
and the vent sizes are shown in Figure 3. The actual CFHT dome dimensions are shown in Figure 4 for
reference.
The vent edges were outlined with acrylic pens to improve their visibility in the water.

Figure 1: Geometry of placement of the small vents on the dome.
The vents are centered on the dome "equator", where the zenith
position is mapped to a pole.
Figure 2: Geometry of placement of the large vents on the dome.
The lower edge of the vents is at the elevation on the dome as for
the small vents.

Figure 3: Vent dimensions in inches. The “spring line” refers to the
equatorial plane normal to the zentih described inFigure 1.
Figure 4: Actual CFHT dome dimensions
for reference.
The 3D printed components were cemented to the dome using two-part epoxy and cyanoacrylate
adhesive. Gores made of 100 μm mono-filament sewing thread were attached to the dome at 7.5
degree azimuth increments using cyanoacrylate. A simple in-house jig was used involving a rotational
table and an arm to hold the taut fishing line at the correct height when applying the thread (on which

adhesive had been applied) to the dome. These steps required great care to avoid having the
cyanoacrylate spread on the dome or have its vapors fog up the acrylic. Thoroughly wiping all surfaces
with denatured alcohol prior to work helped minimize fogging.
The observatory model was mounted on a plywood cutout model of the terrain at CFHT. The terrain
was a scale replica taken from a topographic map, and was made by Eli Hart as part of his internship at
CFHT in the summer of 2010. The terrain was oriented so that the east side was directly facing the
flow direction in the water tunnel, which corresponds roughly to the median prevailing wind direction
at the observatory. The terrain model consisted of 8 layers of 3/8” marine grade mahogany plywood
mounted on a 91.4 cm x 74.9 cm x 3/8” (36” x 29.5” x 9.5 mm) rectangular base sheet. The base sheet
had a rounded leading and trailing edge to reduce surface effects in the water tunnel. The scaled
height represented by the terrain (not including the base sheet) is 12 m; this corresponds to 1.5 m of
elevation per step in the terrain. All wooden parts were treated with at least one primer paint coat
followed by 2 coats of exterior grade acrylic based white paint. Despite this, some minor delamination
of the plywood was noticed on the fourth day of testing.
Figure 5: View of the south side the small vent dome model
The azimuth angles written on the dome base ring correspond to the direction of the slit (shutter
aperture) with 0 degrees at north, 90 degrees to the east, 180 degrees to the south and 270 degrees to
the west with a fixed fiducial set directly south.
3 Testing in Waimea
A plywood and glass tank with cross sectional dimensions similar to that of the UWAL water tunnel
was constructed by Roger Wood for use at HQ in Waimea. This was used to test visibility of the model

Figure 6: View through the shutter aperture showing the aluminum base ring on which the gear was
milled.
Figure 7: The three model domes, from left to right; large vents, unvented and small vents.

Figure 8: Closeup view of the small vent dome showing the
telescope model. The aluminum block right of center of the
telescope represents the freight elevator, while the aluminum
segment representing the mezzanine is in the foreground.
in the water, determine optimal lighting and camera positions, dye injection using a hand syringe, and
check for other other unforeseen logistical issues. A “dry” run with the video cameras was performed
at night in the HQ parking lot to simulate realistic lighting conditions to be encountered at the UWAL
facility.
The tempered glass used in the tank was 3/8” thick; the tank had windows on both sides as well as at
the bottom, similar to the UWAL water tunnel.
Figure 9: The plywood and glass testing tank used to test model visibility and other logistic issues
in Waimea. Slightly leaky, but serviceable!

4 Dye Probe Locations
Dye probe ports were installed on the telescope floor, inside the, in the Cassegrain baffle and at several
locations on the terrain. The probe ports consisted of 9/32” (7.1 mm) brass tubing fitted with Delrin
caps and packed with dense open-cell foam (art foam) to provide friction. The Delrin caps were drilled
to allow insertion of 17 gauge 304 stainless hypodermic tubing. The inner and outer diameter of the
tubing was 0.047” (1.19 mm) and 0.058” (1.47 mm), respectively. With this arrangement the stainless
tubing could be easily moved up and down through the port to adjust the height of the probe in relation
to the model. The probes external to the model (labeled “B” below) had a 90 o , 0.25” radius bend, ~0.5”
(12.7 mm) long formed to allow the dye to be injected into the flow in a more laminar nature. The dye
ports were labeled as follows;
Inside the dome:
A1: Probe installed so that the dye exits at the level of the Cassegrain mirror fold above the
primary mirror.
A2: Probe on the north side of the telescope pier at a 2” (50.8 mm) radial distance from the
dome center.
A3: Probe on the east side of the dome (same radial distance from the dome center as A2).
A4: Probe on the south side of the telescope pier (same radial distance as A2).
A5: Probe on the west side of the telescope pier (same radial distance as A2).
Outside the dome:
B1, B2, B3, B4, B5: Probes from North to South respectively on the upwind (east) side of the
dome, 7.5 cm distant from the building measured along an east/west line.
B6: Probe located directly upwind (east) on the down-slope of the terrain, 20.7 cm from the
dome building as projected on the horizontal plane.
B7: Probe located directly downwind (west) of the dome, approximately 4 cm from the
building.
Probes B1 to B7 could be inserted to be at any level, from a maximum extension in level with the
mezzanine to being totally retracted in their grooves; this permitted us to visualize the flow at various
heights above the terrain.
5 The UWAL 30” Water Tunnel Facility
The UWAL 30” water tunnel is located in the Aerodynamics Laboratory on the UW main campus in
Seattle Washington. Jack Ross (electrical engineer) is the business manager for the Kirsten Wind
Tunnel as well as for the water tunnel facility. The water tunnel itself is maintained by Robert Gordon
(research engineer) and was originally built by professor Robert (Bob) Breidenthal and his students.
Following is the contact information for these individuals:
Jack Ross: 206 543-0439, jwross@u.washington.edu
Robert Gordon: 206 685-3011 (office), 206 713-2971 (cell), deepsnow@aa.washington.edu
Robert Breidenthal: 206 685-1098, breident@aa.washington.edu
The CFHT staff involved in performing the tests in Seattle were Karun Thanjavur, Tom Benedict and
Marc Baril. Derrick Salmon observed and provided guidance via internet teleconference from Waimea.

Figure 10: Dye probe port locations on the model
Figure 11: Dye tubing running to the probes B1-B5 (blue) and B6 (red). Note the brass handles used
to lift the model out of the terrain to allow for easy interchange of the domes, installation of the vent
plugs and the windscreen plugs.
The model was mounted upside down in the water tunnel with approximately 15 mm of the base plate
submerged so that the rounded-over leading edge was halfway submerged. The total cross section of
the model was 960 cm 2 , which corresponds to a blockage ratio of 20.6% with a 62 cm water tunnel
depth.
The water tunnel is located in the Fluid Dynamics lab, along with several other graduate student
research areas and experimental set ups. The water tunnel is approximately 9-10 m long and consists
of a test section 0.7 m wide by 0.7 m deep and 2.5 m long. The water flows through the test section
down into a ~40 cm pipe back to a large centrifugal pump that sets up the flow. After exiting the pump
the water enters a very wide section of tunnel in which a ~3-4 m wide bank of plastic drinking straws
have been packed together; these act to set up laminar flow conditions in the tunnel. The tunnel then

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.

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.

6.3 Video capture
Two Panasonic Lumix ZS7 digital cameras were used for the video capture. This camera was selected
based on a combination of video quality (1280:720 @ 30 Hz), flexibility (10X optical zoom), price
($200) and ready availability. The video was captured in AVCHD “Lite” format (.MTS file extension)
with the highest compression mode selected to minimize the amount of data to be handled later. It was
determined that these settings would not reduce the quality of the captured video in a meaningful way.
The optical stabilization and GPS modes of the camera were disabled to maximize battery run time.
Between the two cameras, three spare batteries were used with a typical run-time on a single charge
being approximately two hours. The time required to charge the battery was ~1 hour. Both cameras
were mounted on high quality, sturdy tripods. One camera viewed through the side of the tunnel (the
“sideview” camera), while the other was mounted close to the floor below the test section and looking
up through the bottom window (the “bottom view” camera). The side view camera was mounted upside
down so that the dome orientation appears correct in the video but the storyboard text is inverted.
Two storyboards were made visible in the side-view video frame, each describing the relevant details of
the experimental setup for that video. The storyboard is correct in all instances except for the
“boundary layer investigation” experiment (described below) where the dome angle appearing on the
board is 0 degrees but is in fact at 90 degrees (which is clear from the video). White board markers and
erasers were used to edit the storyboards (seen in Figure 12).
6.4 The capture sequence
Each video capture instance generally followed the sequence below:
• The side-view camera was started first with the operator (Marc Baril) simultaneously calling
out, “Start”. This call-out is not always heard on the video.
• The bottom-view camera was started with the operator (Tom Benedict) calling out, “Rolling”.
At this point both cameras were capturing video.
• The dye probe operator (Karun Thanjavur) would start the slower of the two dye pumps running
(assuming two dyes were used), wait a few seconds and then start the faster pump. We then
waited a couple of seconds for the pressure in both dye lines to build up. The hose clamps on
both lines were then released simultaneously with Karun calling out, “Open”. Usually, either
Marc Baril, Robert Gordon or a UWAL student would assist with the task of opening one of the
hose clamps.
For flushing time tests, the dye injection lasted for ~3sec, after which the hose clamps were shut off (on
the call, “close”), and the dye pumps turned off. For flow visualization, dye flow was maintained long
enough to provide adequate footage of the flow pattern that was being investigated. For visualizing the
flow upstream and downstream of the dome simultaneously, dye was injected through the downstream
B7 probe first, then B6 (with B7 still running); after a few seconds of both probes injecting, B7 was
turned off, then B6 a few seconds later. For flow visualization around the dome using probes B1 to B5,
the output of the micro-pump was connected to an aquarium air-line gang valve which then fed all five
probes. In this test, for the sake of visual clarity, dye was injected through only one probe at a time by
opening the appropriate valve.
7 Determination of the Operating Tunnel Flow Speed
The first experiment carried out involved the determination of the water flow speed in the channel

above which a transition between laminar flow over and around the terrain to turbulent flow would be
obtained. A set of visualization tests were performed with the upwind terrain probe B6 set at various
elevations above the model while varying the flow speed from 10 to 50 cm/s in increments of 10 cm/s.
At the time the experiment was conducted we believed that we saw a transition in the flow pattern from
a 10 cm/s to 20 cm/s free flow water speed in the tunnel. Namely, the clear formation of a vortex on
the leading edge of the observatory building with a scaled height of 5-6 m. However, examination of
the video footage after the fact does not lend evidence for this. The video stills in Figure 13 with the
B6 probe set 50 mm above the model terrain indicate that the vortex is present and of similar size at all
the flow speeds investigated (side view images). Furthermore, the profile and extent of the wake
around the building does not change in a noticeable way when looking at the top-down view.
The flow speed of 30 cm/s was used for all but a few of the tests. This speed was selected partly on the
basis of remaining well above the velocity of the perceived transition between 10 and 20 cm/s. Other
factors that influenced this choice was that operation above 40 cm/s for extended periods of time was
discouraged by the UWAL staff and that the flushing time (from some quick undocumented tests with
the unvented dome) was found to be short enough to allow efficient progress of the experiments while
being long enough to allow accurate measurement of the flushing time.
Note that at 30 cm/s the Reynolds number Re associated with an ideal spherical obstruction of diameter
L is;
Re= ρ VL
μ =999.7(kg /m3 )⋅0.3(m⋅s −1 )⋅0.2 (m)/1.307x10 −3 ( N⋅s⋅m −2 @10 o C )=4.6x10 4
where ρ is the density and μ is dynamic viscosity of water at the test temperature (average of ~10 C
over the testing period). The dynamic viscosity of air depends primarily on temperature; at 0 C it is
1.35x10 -5 N s m -2 . The air density at 4200 m is 0.80 kg/m 3 and with 32 m diameter dome the wind
speed to which the above model Reynold's number corresponds to in the real-world observatory is 2.4
cm/s. For comparison, the median wind speed at the location of CFHT on the summit of Mauna Kea is
15 knots (7.7 m/s); which is over 300 times greater than the scale speed obtained in our water tunnel
experiment.
8 Description of the tests performed
8.1 Parameters investigated
The basic parameters that could be varied in the tests were as follows (numbers in parentheses indicate
the possible number of free parameters involved with each item):
1. Water flow speed (1): Except for some quick investigations, this was kept fixed as the
dynamics of the flow would not change significantly unless order of magnitude changes were
made to the speed. The flow rate was set to 30 cm/s.
2. Dome configuration (3): Unvented dome, dome with small vents, dome with large vents.
3. Dye probe locations. This was narrowed down to a few configurations for the bulk of the tests.
Inside the dome (2): Probe A1 alone, and probes A3 & A5 combined. This was used for
determination of dome flushing times.
Outside the dome (1-2): Probes B1-B5 fired off in succession to view flow around and into the
dome (this was not done for all the dome types), and probes B6 and B7 fired off in succession
to view flow around the dome on the upwind side and the reverse flow on the downwind side.

4. Windscreen position (3): Either the windscreen was down, 50% raised or 100% raised.
5. Vent plugs (3-4): The purpose of the vent plugs was to simulate throttling of the flow by
completely closing some of the proposed dome vents. We investigated two configurations; one
in which the upwind vents were closed and the slit was facing partially or completely upwind,
with the windscreen at different positions, another with similar dome orientations but with the
vents closed on the downwind side. For each configuration the maximum number of vent plugs
were installed in the dome (up to 3 plugs) and a fixed set of experiments was run in each
configuration, removing a single vent plug once a set of experiments was complete.
At the time of the experiment, the configuration of vent plugs tested represented the most likely
real-world operational configuration of the dome. Hypothetically, with the upwind vents
blocked, the effect of the wind on the telescope shake would be minimized. On the other hand,
having the down-wind vents closed allowed us to investigate the potentially compromising
effect on flushing time having these vents closed. The reason we might want to have these
vents closed is that there was an indication (prior to the tests, but later borne out by our
experiments) that the downwind counter-flow might lead to entrainment of the warm air from
the building exhaust into the dome.
6. Dome position (4-13): The number of dome positions investigated for each dome configuration
depended on the particular configuration with the vents and windscreen plugs installed. With
the exception of the boundary layer investigation test, the dome positions explored were from
90 o (dome slit facing east) through 180 o (dome facing south) to 270 o (dome slit facing west) in
increments of 15 o . This was the case for each configuration in which the vent plugs were not
installed. The north facing orientations were not explored due to the symmetry of the model
and the lack of visibility into the dome with the slit facing north (due to the opaque dome
shutter). Note however that the symmetry is not perfect due to the structures on the dome floor
(e.g. the mezzanine on the south side of the dome floor). Note that in some configurations with
the vent plugs installed, small angles to the ENE were explored.
Typically, after 20 or more tests had been performed, the videos were downloaded to a laptop. This
minimized the possibility of data loss as well as the loss of sequencing of the video files between the
two cameras. Care was taken to erase the camera memory after each download session so that file
names on the side-view and bottom-view cameras would match. The laptop was backed up to an
external disk every evening once testing for the day was complete.
Most of the routine experiments involved first installing the maximum number of plugs (on a given
upwind or downwind side) that would be used with a set dome (if applicable). The data taking would
proceed by taking video at the defined set of angles for a given configuration (see next section for
details), almost always in increments of 15 degrees. The probe configuration would then be changed
and a new sequence of video at the relevant angles would be taken. This provided the smoothest data
taking work flow. However, a few experiments did not fit this mold and these are described below.
8.2 Boundary layer investigation
This was previously described in “Determination of the Operating Tunnel Flow Speed”.
8.3 Flow Visualization Near the Heat Vent Locations
The purpose of this experiment was to determine if the fluid in the vicinity of the heat vents to the NW
and NE of the observatory could be drawn into the dome from certain orientations. The location of the
heat vents was visually estimated referring to the topographical map shown in Figure 14. A hand held

Figure 13: Still frames of boundary layer visualization experiment with probe B6 set at a 50 mm
height above the terrain. Side view (left) is looking due north and the top view is shown on the
right. Variations in dye contrast are due to the effect of the varying flow speed at fixed dye injection
rate (the dye is more diffuse at the higher velocities). The top view images (right) have been
processed to improve the contrast of the blue dye.

dye probe was held near each vent location to visualize the entrainment of dye towards and into the
unvented dome model.
8.4 Turbulence Generator Investigation
Robert Breidenthal suggested that if we wished to increase the level of turbulent layer up to the level of
the dome that we could install some turbulence generators upwind of the dome. In practice this is
unlikely to be feasible, however to give this idea a try we cut a sawtooth shaped turbulence generator
board out of corrugated plastic poster-board with teeth 38 mm tall and 19 mm wide at the base. This
structure was held on the upstream edge of the model base plate and the flow was visualized using dye
probe B6. The depth of the turbulence generator in the water was varied to determine at what point it
had an effect on the vortex on the upstream side of the observatory base. The turbulence generator
board is shown in Figure 15.
9 Basic Data Product
The files were saved in the AVCHD Lite format of the Panasonic ZS7 cameras. There were a few
issues around using the files in this format. For one, the AVCHD format is not commonly supported by
older video display software; this is a fairly easy problem to work around. Secondly, we wished to use
MATLAB to automatically process the video to determine the flushing times in a more quantitative
way, however this video format is not supported by MATLAB. Thirdly, the 720p HD format video was
unnecessarily large for most common use and precluded easy distribution on inexpensive data media
(e.g. DVD disks).
The video files were first renamed and organized in a self-explanatory and intuitive path structure that
makes it easy to navigate to the video pertaining to a specific experimental configuration. These files
were then converted using the SUPER video conversion tool to a AVI format using the following
settings:
• Format: AVI
• Output video codec: DivX
• Output audio codec: mp3
• Video scale size: 640 x 360 pixels
• Frame per sec: 14.985 Hz
• Bitrate: 9600 kbps
• Options: Hi-quality
• Audio: 1 Channel, 22050 Hz sampling, 96 kbps bitrate
• MEncoder and DirectShow decode selected (the latter only works for the Windows OS).
Down-conversion from the nominal 60 Hz (30 Hz actual!) frame rate to 15 Hz was necessary to ensure
normal playback speed of the video. Conversion to the actual 30 Hz frame rate of the video resulted in
video that played back at approximately twice the correct speed; this was found for at least 4
conversion packages tried. This problem is related to the decoders of the AVCHD Lite format ignoring
a bit that indicates that each 30 Hz frame should be played twice to achieve the nominal 60 Hz
playback.

Figure 14: Topographic view of the summit showing the building heat exhaust vents. South is on the
bottom, west is to the left.
Figure 15: Turbulence generator installed on the up-stream edge of the model base plate.
Scale is 6" (15 cm) long.
The AVI files were saved with file names identical to the AVCHD files (.MTS extension) but with the
“.avi” extension appended. The path structure was maintained when converting to the AVI format files.
The path structure showing the different experimental configurations used is shown in Figure 16,
Figure 17 and Figure 18. Unless noted otherwise the dome angle ranges in these figures indicate data
taken at 15 degree increments inclusive of the angles at the extremes of the range.

10 Lessons learned
• A dome shutter made of a transparent material would have been helpful and the same could be
said for the vent plugs; in some orientations the dome shutter or vent plugs considerably
blocked the view of the flow inside the dome.
• All aluminum parts on the inside of the dome (e.g. the dome floor) should have been painted
white to improve the contrast with the dye. The telescope would then have to be painted a
bright contrasting color to stand out against dome floor. Choice of this colour should be such
that it is not confused with any of the dyes used.
• The use of fluorescent or other lighting fixtures with a strong periodic intensity variation should
be avoided. In this case the 60 Hz frequency of the fluorescent panel intensity time variation
was a very close multiple of the 30 Hz camera frame rate which led to low frequency “beats” in
the background intensity that appear to have a chromatic component.
• A vent in the base of the model should have been provided to allow air to be released from
inside the dome when it is inverted in the water. In our tests we used a siphon to remove the air
from the dome, which was effective but very awkward.
• A model of the MKAM/weather tower would have been useful to see the effect of the dome
wake at this location.

Figure 16: Path structure used to organize the captured video files. Page A: file
breakdown for the large vent dome. Items in yellow are folders, items in blue are the files
contained in the bottom level folder. Continued on pages B and C.

Figure 17: Path structure used to organize the captured video files: Page B: file
breakdown for the small vent dome. Items in yellow are folders, items in blue are the files
contained in the bottom level folder. Continued on pages A and C.

Figure 18: Path structure used to organize the captured video files. Page C: file
breakdown for the unvented dome. Items in yellow are folders, items in blue are the files
contained in the bottom level folder. Continued on pages A and B.

11 University of Washington 36” Wind Tunnel Tests
11.1 Overview
Having successfully completed all our tests in the
UWAL Water Tunnel facility ahead of schedule, on 11
March we were given access to the 36” wind tunnel
facility for half a day of preliminary tests in preparation
for the full scale wind tunnel tests planned for later this
year. The principal objectives were to test the structural
integrity of the water tunnel model under the more
rigorous operating conditions in the wind tunnel, as well
as to explore options for flow visualization and flushing
time tests. Here we document our findings and lessons
learned to provide a reference for work to follow.
Figure 19: View of the UWAL 36” wind
tunnel shownfrom the inlet end, looking
toward the testsection and the power unit at
the rear.
11.2 UWAL 36” Wind Tunnel
The UWAL 36” wind tunnel is housed in an
independent building adjoining the Kirsten wind tunnel
facility. This single story building is completely
devoted to the wind tunnel, so there is no intrusion with
any other laboratories or office space. The wind tunnel
uses an open circuit, straight through design, with an
inlet filter and baffle section, tapering down to the test
section, then diverging to the single propeller power unit at the exhaust end.
The test section has a rectangular, 36”x36” cross section, and is 8’ long. Both sides and the top are
made of plexiglass, with steel strengthening members which offers clear visibility of the model being
tested for a wide range of viewing angles. Since the wind tunnel is located in the middle of the
building, there is adequate room ( > 10’) between the building walls and the test section for convenient
placement of cameras, lights and video equipment. This wind tunnel does not have any lighting
equipment, so all the necessary lights with tripods will have to be provided by us.
The floor of the test section has a rectangular opening, ~2’6”x2’, closed by a wooden trap door on
which the model is mounted (see Figure 21). The trap door is bolted from underneath, making access
easy. In addition, one of the side walls of the test section is a hinged window running almost the entire
length of the test section, which thus provides free access to the model between tests (and is of course
kept closed during testing).
The power unit is a variable pitch propeller driven by an electric drive (Figure 20, right). The wind
speed is controlled manually by adjusting the pitch of the blades through a hydraulic control
mechanism. The free stream wind speed in the test section is measured using a U-tube manometer
(Figure 20, left) one end of which is connected to a fixed point on the upwind side and the other to the
test section. The differential reading on manometer has been directly calibrated to wind speed. The
maximum wind speed at which the unit may be run continuously is 140 mph.

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

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.
Figure 22: (Left) Tufts used for flow visualization, outside the telescope building, around the dome, as
well as the wake of the telescope superstructure. (Right) Tufts fixed to a long hand-held probe and
scanned to visualize the flow at various points.
11.3.3 Flow visualization with china clay
At UWAL, they also use china-clay mixed with kerosene, in a thick soup, to trace the flow pattern. For
this test, the model is ‘painted’ with this china-clay/kerosene mix in the areas where the flow is to be
visualized. The flow is then quickly brought up to operating speed, so that the china-clay/kerosene mix
flows into patterns representing the actual airflow on the surface of the model. Within a few minutes,
the kerosene evaporates leaving the china clay fixed in position. This sequence is clearly seen in the
before and after images shown in Figure 21. It is to be noted that the china-clay mix was only applied
all around the exterior of the telescope building. However, the flow removed most of the mix from the
upstream side and smeared it along the sides and behind the telescope building, as well as up on to the
rear of the dome due to the backwash. This is a very powerful technique to identify actual points of
flow separation, eddy formation and so on. After the testing, the dried china clay may be removed using
a damp cloth.
11.3.4 Lessons learned
• If we're planning to visualize with China clay, we need to paint the model black and make it
easy to wipe down.
• There is a removable top panel as well that we should probably make a custom unit for so we
can have an unobstructed top-view camera and lighting.
• Using a smoke wand for flow visualization at 140 mph is not practical
• Everyone wears hearing protection when the tunnel is running: no voice communication!
• The audio on the camera is overwhelmed by the sound of the fan: no audio
• sync of multiple cameras.
• There is just one table and a few chairs in the room. No tools, workbenches, etc. We need to

ing everything needed.
• It takes a while to spin the fan up and down, but wind speed changes can be made fairly
quickly. When planning tests, we need to keep this in mind.
• The model can be accessed when the fan is running by feathering the blades to zero wind speed
(e.g. while applying the China clay, so that the fan may be brought to full speed without any
delay.)
• The camera on top of the wind tunnel is not easy to access. Having remote control over one or
both cameras would be beneficial, though not necessary.
• Everything that enters the room must be carried down a flight of stairs.
Appendix 1: The UWAL tuft-making loom
Figure 23 shows the design of the loom used at UWAL for easily making long strips of tufts for
flow visualization. The loom consists of an aluminum channel section, ~6” wide, (shown in grey)
with three or four wooden rails (in yellow), about ~1” apart, and running the length; the length of
the channel is about 3’. The tuft yarn is woven across the channel, going through the opposite
slots in the side members. A long piece of Scotch tape is then used to fix the yarn along the
length of each of the wooden rails. The yarn is then cut on one side only in each of the gaps
between the wooden rails and also the sides of the channel, leaving ~1” lengths of yarn stuck to
the Scotch tape. The tape is peeled off with these tufts stuck to them and fixed where required on
the model.
Figure 23: Design of the UWAL tuft making loom.

Appendix 2: Packing List
Weight and volume limitations for shipping by Fedex are; 150 lbs weight, 119” length and 165" in
length plus girth (L+2W+2H). This required shipment of the model in two ABS shipping containers
(43”x21”x28” & 16”x25”x35”).
Tool List:
Terrain + Side Panels
Side Blocks, 6x Fender Washers, 6x Thumb Screws
Building + Mezzanine, 4x Thumb Screws
3x Domes (Unvented, Small Vents, Large Vents)
Telescope Model
2x Cameras
2x Tripods
Tools (See Next List)
Shop Towels
11x Dye Probes (stainless, hose, syringes, etc.)
11x Dye Probe Mating Hardware (to mate our probes to their pumps)
30x Spare Probe Material (SS tubing, Teflon tubing, Syringes, etc.)
Magnet Board + Run Parameter Labels
Handheld Flash Unit
Wind Screen Tape (same as previously tested)
Vent Plugs (Solid Litho - Steve)
Windscreen Plugs (Solid Litho - Steve)
Blocking Foam
Light Stands
Black Cloth
Gaffer's Tape and/or Duct Tape
Screw Drivers
T-Handle Ball Drivers
Acrylic Paint Pen
Magic Marker
Sand Paper Assortment
Needle File Assortment
Large file assortment
Small tools toolbag (Tom Benedict's)