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.

Appendix A: Force Balance Test Data

Appendix B: Sketch of Proposed Interferometer Set-Up

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.