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
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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.
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.