the university of manitoba in the thermofluids research...
Post on 12-Feb-2018
220 Views
Preview:
TRANSCRIPT
THE UNIVERSITY OF MANITOBA
RESEARCH PROJECTS IN THE THERMOFLUIDS RESEARCH LAB
Work Term Completed at:
The University of Manitoba Thermofluids Research Lab
238 Engineering Bldg. Winnipeg, Manitoba
R3T 5V6
by Brett Crawford Department of Mechanical Engineering
First Co-op Work Term Summer 2004
In partial fulfillment of the requirements of the Engineering Cooperative Education
Assignment: I – 25.205
Presented to: Professor N. Richards, Director
Mechanical and Manufacturing Engineering Cooperative Education Program
356 Engineering Bldg. Winnipeg, MB
R3T 5V6
September 15, 2004
Summary
This report will cover the two research projects I was involved in during my
summer work term at the University of Manitoba Thermofluids Engineering Research
Laboratory. This includes the operation and calibration of a force measurement system,
as well as the design, construction, and operation of an interferometric temperature
measurement system.
Working with the Force Measurement System involved familiarizing myself with
the new experimental apparatus in the laboratory, and then calibrating and verifying that
it was in good working order. This included designing a way to verify that it was working
properly, and consulting with the manufacturer. It was determined that the balance was in
good working order, and future projects using the balance are recommended.
This report will also cover my work designing, constructing, and working with an
interferometric temperature measurement system. This includes performing preliminary
experiments to ensure it was working properly, and then setting up and testing the
interferometer in various configurations so it could be used in the icing tunnel. The report
will also cover future projects to be done with the interferometer in the laboratory, such
as designing a permanent structure so it may be used in the icing tunnel.
Table Of Contents
List of Illustrations v
I. Introduction 1
II. Background 2
A. Research Facility 2
B. Research Interests 2
III. Problem 3
A. Research Facility 3
B. Industry 3
IV. Research Projects 4
A. Force Measurement System 4
i. Apparatus 4
ii. Operation 5
iii. Calibration 5
B. Interferometer 7
i. Theory 7
ii. Construction 11
iii. Tests and Results 12
iv. Icing Tunnel 14
V. Future Projects 17
A. Force Balance 17
B. Interferometer 18
VI. Conclusion 19
VII. Appendices 20
A. Appendix A: Sample Force Balance Test Data 20
B. Appendix B: Sketch of Proposed Interferometer Set-Up 26
VIII. References 28
List of Illustrations
Figure 1: Force Balance and Coordinate System 4
Figure 2: Hanging mass used to apply moments and forces on Force Balance 6
Figure 3: Schematic Mach-Zehnder Interferometer 7
Figure 4: Schematic Fringe Shift in Wedge Fringe Mode 9
Figure 5: Interferometer in Thermofluids lab 11
Figure 6: Sequence of Heated Vertical Plate Interferometric Output 12
Figure 7:Interferometer outputs with: i. heated aluminum plate, ii. vertical ice cube 13
Figure 8: i. Interferometer Set up on Plexiglass Duct, ii. Mounted inside Icing Tunnel 16
I. Introduction
The subject of this report are the research projects I was involved in during my
summer work term placement at the University of Manitoba Thermofluids Engineering
Research Laboratory. I was responsible for two projects: calibration of a Force
Measurement System, which was to be used in the laboratory; and working with an
interferometric temperature measurement system.
The first project involved the operation and calibration of a force measurement
system for use in the laboratory. This was a new system that had never been used in the
laboratory. My assignment was to familiarize myself with the system, and calibrate it to
ensure it was in good working order for experimental use.
The second project that I was assigned was the design, construction and operation
of an interferometric temperature measurement system. This was also a new technology
to the lab. Once constructed, I was to familiarize myself with the operation and possible
uses for the interferometer. I was then responsible for designing a way to use the
interferometer for fluid temperature measurements in the icing tunnel.
II. Background
A. Research Facility
The Thermofluids Engineering Research Laboratory is located in room 238
Engineering Building at the University of Manitoba, and is overseen by Dr. Greg Naterer.
Opened in 2003, the lab consists of a water and spray flow/icing tunnel with PIV (Particle
Image Velocimetry) and flow visualization, pulsed and continuous wave laser systems
(Nd: YAG), an interferometer, and heat transfer data acquisition modules. The central
experimental apparatus in the laboratory is the icing tunnel, which is essentially a large,
modified wind tunnel. The icing tunnel has both wind and wind/rain capabilities, with a
maximum wind speed of 120km/h. In addition, the tunnel has a precision digital
temperature control, which maintains the air temperature inside the tunnel within a
controlled range of -40°C to 40°C.
B. Research Interests
Current research at the Thermofluids Engineering Research Laboratory
encompasses many industries and applications, including aerospace industries, and
alternative energy generation. Presently, Manitoba Hydro is interested in the effects of ice
formation on wind turbine blades, and GKN Westland Helicopters is sponsoring research
on ice formation on aerospace components.
III. Problem
A. Research Facility
Due to the fact that the research facility is still relatively new, many experimental
apparatus are still in the design and construction stages. The force balance measurement
system, originally purchased from Allied Aerospace in 2002, has never been used, and
thus needed to be calibrated before it was used experimentally. Another project in the lab
is designing a way to take accurate fluid temperature measurements. In order to take non-
intrusive temperature measurements, it was desired that an interferometer be constructed
in the lab. Although Bryce Saunders first laid down the framework for interferometry to
be used in the lab in his 2003 undergraduate thesis, an interferometer had never been built
in the lab.
B. Industry
There are many industrial problems that motivate research in this facility. One of
the main concerns is ice formation on various structures, and the related problems. As a
result, much of the research involves multiphase fluid flows and associated heat transfer
problems. Manitoba Hydro is in the process of exploring the use of wind turbines as an
alternative energy source here in Manitoba. However, there are many issues associated
with the build-up of ice on the turbine blades and how this affects the efficiency of
energy generation. There are also numerous aerospace companies who are interested in
ice formation on aerospace structures, and how to mitigate this problem.
IV. Research Projects
A. Force Measurement System
The Thermofluids Engineering Research Laboratory is equipped with a Force
Measurement System, which was designed and built by Allied Aerospace for use in the
icing tunnel. The Force Measurement System provides a way to accurately measure static
and aerodynamic loads on a given test piece in the tunnel.
i. Apparatus
The Force Measurement System consists of a model support assembly and a data
acquisition system. The model support consists of two balances mounted on rotary tables,
and a support structure, as shown below.
Figure 1: Force Balance and Coordinate System
As shown in Figure 1, the balance measures axial force (Fx), normal force (Fz), rolling
moment (Mx), pitching moment (My), and yawing moment (Mz). The force component in
the y-direction (Fy) is not measured. A test piece is mounted between the two balances by
clamping to the 5/8 inch diameter cylindrical mounts that protrude from the balances.
Two cables carry raw millivolt readings from the balances to the data acquisition system,
where the voltages are processed and transformed into force readings.
ii. Operation
The balances mounted on the rotary tables are made of stainless steel, and include
flexures, used to measure three components of force and moments with high precision.
The stand-alone data acquisition/processing system consists of a HBM MGC Plus data
acquisition system connected to a PC via Ethernet. There are eight channels of millivolt
data that are read from the balance and processed by the data acquisition system. These
eight channels are linearly combined into six channels, which are multiplied into an
array, then multiplied by a selected matrix to give metric or imperial units of force and
moments. The software installed on the computer displays real-time force and moment
readings in the selected units.
iii. Calibration
In order for the Force Measurement System to be used experimentally, we
required a way to test if the balance was reading forces and moments accurately. I was
responsible for designing a method of testing the system, and then verifying that the
system was indeed working properly. For a test piece, I used a rectangular piece supplied
by Allied Aerospace with counterpunched indents in the surface on all sides. I then
applied known forces and moments and recorded the readings of the system. By hanging
a known mass from a bent metal rod, I could apply different moments and verify the
system was reading the same moment. Figure 2 below demonstrates how I applied forces
and moments to the test piece.
Figure 2: Hanging mass used to apply moments and forces on Force Balance
The white marks on the test piece in the figure above mark known distances on the test
piece, so I could move the mass around (change the moment by a certain amount) and
record the system’s response. I tested Fx, Fz, Mx, My, and Mz in both metric and Imperial
units, and the results were very promising. For a sample of the detailed results obtained
during testing, please consult Appendix A: Sample Force Balance Test Data.
Once I finished testing and recording test data on the balance, I sent the results to
Allied Aerospace, to confirm that the results obtained were a satisfactory indicator that
the balance was working properly. Unfortunately, due to construction on the icing tunnel,
I was unable to run any further tests using the Force Measurement System during my
work term.
B. Interferometer
In order to accurately predict and measure ice build up on certain structures in the
icing tunnel, an interferometer was to be designed and built. The interferometer would
provide a non-intrusive method of fluid temperature measurement, and has many
advantages over existing methods of temperature measurement, such as thermocouples.
My role was to design, build and operate an interferometer that could be used to measure
fluid temperatures in the icing tunnel.
i. Theory
An interferometer is basically a very simple device that considers the wave nature
of light to measure temperature fields. We chose to build a Mach-Zehnder type
interferometer, because of its inherent simplicity and variety of applications.
Figure 3: Schematic Mach-Zehnder Interferometer
Figure 3 shows a schematic diagram of a Mach-Zehnder interferometer. A
monochromatic light source is first passed through a lens in order to expand the beam
into a parallel, expanded monochromatic light source. The expanded light beam is
incident upon the first beam splitter, SP1, where it is split into two separate coherent light
beams. The transmitted light strikes mirror M1, and is reflected towards the second beam
splitter SP2. The light that is reflected from SP1 travels to mirror M2, where it is reflected
towards the second beam splitter. The second beam splitter transmits half of light beam 2,
and reflects half of light beam 1, where they are recombined and projected onto a screen.
Note that there is a second recombined beam (parallel to beam1) that may be used to
view the identical image on a screen. The final recombined beam is essentially beam 1
and beam 2 superimposed. Since both beams come from the same source, they are still
coherent and may interfere. If both path 1 and path 2 are exactly the same, there will be
constructive interference, and the output will be a uniform bright spot. This is called the
‘infinite fringe’ mode. However, when the beams are intentionally slightly misaligned
upon recombination at SP2, a path length difference will be introduced, and there will be
a ‘fringe’ pattern of varying light and dark lines produced on the screen. This is called the
‘finite’ or ‘wedge’ fringe mode. When a test piece is introduced in one of the path
lengths, this creates a path difference between the two beams, and subsequently shifts the
fringes from their original positions. When there is heat transfer between the test piece
and the ambient air, the fringe shifts may be used to evaluate local temperature gradients
and the surrounding temperature field.
Figure 4: Schematic Fringe Shift in Wedge Fringe Mode
A schematic of a typical fringe shift pattern is shown above in Figure 4. Note that
fractional shifts are possible (εA), which makes it possible to measure temperature at an
infinite amount of points.
Assuming constant pressure and uniform properties in the test section, the temperature at
a given fluid location may be evaluated from the following equation:
⎪⎪⎭
⎪⎪⎬
⎫
⎪⎪⎩
⎪⎪⎨
⎧
+
⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜
⎝
⎛
+
−= 1
T
T
ref
ref
ελ
ε
RpCL
T Equation 1
Where: T = Temperature at given location (K)
ε = Fringe shift
p = Pressure (Kg/s2m)
C = Gladstone-Dale constant (m3/Kg)
L = Length of test piece (m)
λ = Wavelength of light (m)
R = Ideal Gas constant (m2/s2K)
Tref = Reference (ambient) air temperature (K)
For a thorough derivation of Equation1, please consult reference 2. Note that since the
term Tref appears in Equation 1, there must be a known reference point in the field of
view.
ii.Construction
Due to the sensitivity of an interferometer, the apparatus required a rigid, planar
surface on which it could be mounted. Because I hoped to use the interferometer in a
variety of configurations, I designed a custom table, which was made of extruded
aluminum. The table and optics were totally adjustable, which would allow for a variety
of test pieces to be used, and the interferometer to be operated in a variety of
configurations.
Figure 5: Interferometer in Thermofluids lab
Figure 5 shows the complete interferometer on the custom-built table, including 2 beam
splitters, 2 mirrors, beam expander, and 0.95mW HeNe laser light source. Once
assembled on the table, the optics were aligned, and I started preliminary testing.
iii. Tests and Results
Once the interferometer was aligned, I began running simple natural convection
tests, to ensure that the output of the interferometer was consistent with published data.
With the interferometer aligned in the finite fringe mode, I set-up a screen behind the
final beam splitter, and positioned a digital camera behind the screen. It is important that
the camera be positioned directly behind the screen, so that there is no distortion of the
image due to the camera being placed at an angle to the screen. I found that the best
output was achieved using a plain white piece of paper as a screen, and operating in the
dark. I used a JAI progressive scan digital camera, which was connected to National
Instruments’ IMAQ Vision Builder software on a PC. As there is ongoing research in the
field of natural convection using interferometers, I chose to run similar experiments to
those in current published papers. For my natural convection tests, I used a vertical
heated plate as a test piece and ran numerous tests. Figure 6 shows selected pictures from
a sequence taken during a heated vertical plate test.
Figure 6: Sequence of Heated Vertical Plate Interferometric Output
The first picture shows the fringes at ambient conditions, before the plate was heated. The
following three pictures show the fringes shifting as the plate is heated, thus heating the air
around it.
In addition to testing with a heated vertical plate, there were countless other tests run
with heated pieces of aluminum, cooled pieces of aluminum, and ice cubes. Figure 7 shows
samples of two other configurations that were tested.
i. ii.
Figure 7:Interferometer outputs with: i.heated aluminum plate, ii.vertical ice cube
The preliminary testing of the interferometer was considered successful, as the results
obtained were consistent with published data on free convection. However, this was merely a
stepping-stone towards the final goal of interferometric temperature measurement in the icing
tunnel.
I also ran other tests to observe what happens when the laser beams are passed through
spraying water, as would exist inside the icing tunnel. The water droplets cause the light to
arbitrarily refract, thus rendering the beams incoherent, and wiping out the output. This test
proved valuable, as it revealed a major obstacle to be overcome in order to operate the
interferometer in the icing tunnel.
iv. Icing Tunnel
My initial plan was to set up the interferometer outside of the icing tunnel, and pass the
laser beams through the glass windows. However, after some research, it was found that ordinary
glass is not optically flat, thus rendering the beam incoherent as it passes through (see reference
4). I then began thinking about moving the entire apparatus inside the icing tunnel. However, in
working with the interferometer and the icing tunnel, it became clear that there were numerous
technical problems that needed to be solved. The main issues were as follows:
a. Vibration
Any vibrations induced on the interferometer cause the output to fluctuate. Unless
properly isolated, vibrations from the icing tunnel would cause the output to be washed
out.
b. Cold
With test temperatures inside the tunnel nearing -40°C, the laser and digital camera
would cease to operate normally.
c. Condensation/Rain
The interferometer does not operate when the test beams are passed through spraying
water, as would exist during test situations. Also, condensation build-up on the optics,
laser and camera causes them to malfunction.
Due to these problems, it became apparent that it would not be feasible to simply place
the entire interferometer inside the tunnel. Extensive research and consulting with experts in the
field of interferometry did not yield any sources of published work with an interferometer being
used in a wind tunnel with spraying capabilities. After consulting with Dr. Bibeau, engineering
technician Bruce Ellis, and Dr. Naterer, we decided to attempt to mount the interferometer
vertically, outside of the tunnel. Such a set-up would require a rigid frame hung from the roof of
the laboratory, independent of the icing tunnel. The optics, laser, and camera would be mounted
vertically on this frame. Both the reference and test beams would pass through the test section in
the tunnel, with one of the beams traveling across the desired test piece. This set-up would
require that the beams traveling through the tunnel be enclosed in some sort of cylinder, to shield
the beam from the spray in the tunnel. For a sketch of the proposed set-up, please consult
Appendix B. The proposed set-up would address the following technical problems:
a. Vibration
Because the interferometer frame would be mounted to the concrete roof in the lab, it
would be independent of any vibrations induced by the icing tunnel while in operation.
b. Cold
With the laser and camera both mounted outside the tunnel (on the frame), they would
not be subject to the extreme temperatures experienced inside the tunnel.
c. Condensation/Rain
Because the optics are mounted outside the tunnel, there are not subject to the
problematic environment inside the tunnel. Passing the test and reference beams through
tubes would also eliminate the problem caused by water spray.
When designing this new set-up, it quickly became evident that this would not be a quick, or
inexpensive project. In the interests of a productive and timely conclusion to my work term, Dr.
Naterer requested that I come up with some sort of apparatus that would mimic the proposed set-
up as outlined above, so we could test the idea.
For simplicity, I decided to make a frame that would mimic my proposed set-up and
mount it on top of a plexiglass duct inside the tunnel. That way I could simply drill holes through
the plexiglass panels in the duct, which are easily replaceable. The tunnel would be run at a low
velocity, and at ambient air conditions. Due to time constraints, I decided to mount the
interferometer horizontally (as opposed to vertical) for ease of alignment. Using steel struts from
Unistrut Corporation, I custom designed and built the frame, as shown in Figure 8.
i. ii.
Figure 8: i. Interferometer Set up on Plexiglass Duct ii.Mounted inside Icing Tunnel
Once the interferometer was mounted and aligned, we ran the tunnel (with no test piece) to see if
vibrations would affect the output. Encouragingly, the output was unaffected at low wind speeds
(approx 20km/h). Next, I placed a heated plate in the test section (inside the duct) to test forced
convection heat transfer. The results were very positive. As expected, the fringes shifted
according to the temperature gradients caused by the heated plate. However, due to time
limitations and tunnel conditions, I did not have time to test the interferometer with water being
sprayed inside the duct.
V. Future Projects
A. Force Balance
After working with the Force Measurement System, I was able to verify that it is ready to
use experimentally. There are several projects and experiments that may be performed in the lab
using this system. One of the first projects should be to test aerodynamic loads using the balance
in the icing tunnel. Using a simple shape, (such as a cylinder), one could record the drag force
measured experimentally at a given wind speed, and then compare the results with published
data. Another project involves designing a way to measure static forces on the balance while the
tunnel is in operation (inducing dynamic forces). In order to measure the static forces, the
operator will likely need to block the wind and spray from the test piece/balance while the tunnel
is in operation. Measurement of static forces could be used to assess the center of mass change
while there is ice build-up on a test piece. Such a project would likely involve designing a
‘shield’ that can be erected quickly and remotely while the tunnel is in operation to block wind
and spray.
B. Interferometer
Although I made significant advancements implementing an interferometer in the
Thermofluids Lab, there remains much work to be done. We must continue to mimic our
proposed set-up, and test under various conditions to ensure that it will be feasible. One of the
most important tests is a test with water being sprayed. This would include developing a method
to shield the reference and test beams from the water, and a ‘shutter’ to close over the test piece
when measurements are being taken. I propose using a tube to pass the beams through, which
should sufficiently block the spray. It would also be advisable to attempt to align the
interferometer on a much larger scale (such as would be required if operated outside the tunnel)
to ensure there are no unforeseen difficulties with the optics, or other components.
VI. Conclusion
The research projects in the Thermofluids Engineering Research Laboratory are
constantly advancing and evolving. Although I made many advancements in my projects, there
remains a lot of work to be done.
The Force Measurement System was proven to be ready for experimental testing. There
are currently numerous other projects that may be undertaken with the Force Balance in the
future, including further testing to ensure it is reading properly, and designing a method to record
static measurements during testing.
For my other project, I was able to design, construct, and operate an interferometer to
measure fluid temperatures. I also showed that the interferometer is capable of measuring fluid
temperatures in the icing tunnel. Future projects include testing with water spray, and designing a
permanent structure to use the interferometer to measure fluid temperatures in the icing tunnel.
VIII. References
1. M. Born and E. Wolf, Principles of Optics: Electromagnetic Theory of
Propagation, Interference and Diffraction of Light, 7th (expanded) Edition, Cambridge University Press, 1999.
2. R.J. Goldstein, Optical Techniques for Temperature Measurement, in E.R.G.
Eckert and R.J. Goldstein (eds.), Measurements in Heat Transfer, AGARD, Technivision Services, Slough, England, 1970.
3. W. Hauf and U. Grigull, Optical Methods in Heat Transfer, in J.P. Hartnett and
T.F. Irvine Jr. (Eds.) Advances in Heat Transfer, Vol. 6, pp. 133-366, Academic Press, New York, 1970.
4. D. Naylor and N. Duarte, “Direct Temperature Gradient Measurement Using
Interferometry,” Experimental Heat Transfer, vol.12, 1999, pp.279-294.
5. D. Naylor, “Recent Developments in the Measurement of Convective Heat Transfer Rates by Laser Interferometry,” International Journal or Heat and Fluid Flow, vol. 24, 2003, pp.345-355.
6. X. Wei-ming, W. Yun-gang, and Y. Jian-jun, “Interferometric Investigation in the
Productive Wind Tunnel,” Proceedings of SPIE, vol. 5058, 2003, pp.675-678.
top related