Efficiency Investigation of a Helical Turbine for Harvesting Wind

Northeastern University

Mechanical Engineering Master's Theses Department of Mechanical and IndustrialEngineering

January 01, 2011

Efficiency investigation of a helical turbine forharvesting wind energyNathan WillardNortheastern University

This work is available open access, hosted by Northeastern University.

Recommended CitationWillard, Nathan, "Efficiency investigation of a helical turbine for harvesting wind energy" (2011). Mechanical Engineering Master'sTheses. Paper 40. http://hdl.handle.net/2047/d20001223

Efficiency Investigation of a Helical Turbine for Harvesting Wind Energy

A Thesis presented by

Nathan Willard To

The Department of Mechanical and Industrial Engineering In partial fulfillment of the requirements

For the degree of

Master of Science In

Mechanical Engineering

In the field of Thermofluids Engineering

Northeastern University Boston, Massachusetts

September 2011

ii

Abstract

In recent times, there has been an increased interest in wind energy due to concerns about the pollution

caused by burning fossil fuels and their rising prices. Most wind turbines in use today are conventional

wind mills with three airfoil shaped blades arraigned around a horizontal axis. These turbines must be

turned to face into the wind and in general require significant air velocities to operate. Another style of

turbine is one where the blades are positioned vertically or transverse to the axis of rotation. These

turbines will always rotate in the same direction regardless of the fluid flow. Due to the independence

from the direction of the fluid flow, these turbines have found applications in tidal and surface current

flows. To see how effective this sort of turbine would be in air, a helical turbine based on the designs and

patents of Dr. Alexander M. Gorlov was chosen. His turbine was developed to improve upon the design

of Georges J. M. Darrius by increasing the efficiency and removing pulsating stresses on the blades,

caused by the blades hitting their aerodynamic stall in the course of rotation, which often resulted in

fatigue failure in the blades or the joints that secured them to the shaft. The turbine takes the Darrius type

turbine, which has a plurality of blades arranged transverse to the axis of rotation, and adds a helical twist

to their path, insuring that regardless of the position of the turbine, a portion of the blade is always

positioned in the position that gives maximum lift. This feature reduces the pulsations that are common

in a Darrius type turbine. In his investigations, Gorlov claims that his turbine is significantly more

efficient than Darrius and has achieved overall efficiencies between 30% and 35%. For this

investigation, a helical turbine was tested inside and outside a wind tunnel using an electric generator

(inside tests only) and a torque meter paired with a tachometer to measure the output power of the turbine

and calculate its efficiency. In the end, the turbine did not come close to the claimed 30% efficiency,

reaching at best an efficiency of around 0.35%. Further investigations should be made to determine why

the results from this investigation were as low as they are.

iii

Acknowledgements

First, I would like to express my deep appreciation for my advisor; Prof. M. E. Taslim for guiding me through the process of conducting this investigation.

I would also like to give special thanks to Jonathan Doughty and Kevin McCue for the aid that they have given me in the construction and testing of the turbine.

Thirdly, I would like to give thanks to my colleagues, Mehdi Abedi, Nathaniel Rosso and Adebayo Adebiyi for the hints and tips they have given me through conversation regarding this

investigation.

Finally, I would like to express my gratitude to my family for supporting me in this endeavor.

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Table of Contents Abstract ......................................................................................................................................................... ii Acknowledgements ...................................................................................................................................... iii List of Figures .............................................................................................................................................. vi List of Tables ............................................................................................................................................... ix Nomenclature ............................................................................................................................................... xi Chapter 1 ....................................................................................................................................................... 1

1.1 Introduction ......................................................................................................................................... 1

1.2 Literature Review ................................................................................................................................ 2

Chapter 2 ....................................................................................................................................................... 6 2.1 Overview of Experiment ..................................................................................................................... 6

2.2 Design and Construction of the Turbine ............................................................................................. 7

2.2.1 Overview of Design ..................................................................................................................... 7 2.2.2 Shaft Design ................................................................................................................................. 8 2.2.3 Flange Design .............................................................................................................................. 8 2.2.4 Spoke Arm Design ....................................................................................................................... 9 2.2.5 Blade Design .............................................................................................................................. 10

2.3 Selection of Instrumentation ............................................................................................................. 12

2.3.1 Torque Meter ............................................................................................................................. 12 2.3.2 Tachometer ................................................................................................................................ 14 2.3.3 Generator .................................................................................................................................... 14 2.3.4 Pitot Tube and Manometer ......................................................................................................... 15 2.3.5 Wind Meter ................................................................................................................................ 15

2.4 Test Setup and Procedure .................................................................................................................. 16

2.4.1 Layout of the Test Chamber ....................................................................................................... 16 2.4.2 Wind Tunnel Tests ..................................................................................................................... 17 2.4.3 Out of Wind Tunnel Tests .......................................................................................................... 19 2.4.4 Calibration Check on Handheld Wind Meter ............................................................................. 20

Chapter 3 ..................................................................................................................................................... 23 3.1 Wind Tunnel Tests with Generator ................................................................................................... 23

3.1.1 Results from 0.55in Oil Test ...................................................................................................... 24 3.1.2 Results from 0.60in Oil Test ...................................................................................................... 26 3.1.3 Results from 0.65in Oil Test ...................................................................................................... 28 3.1.4 Results from 0.70in Oil Test ...................................................................................................... 30 3.1.5 Results from 0.75in Oil Test ...................................................................................................... 32 3.1.6 Results from 0.80in Oil Test ...................................................................................................... 34

v

3.1.7 Results from 0.85in Oil Test ...................................................................................................... 36 3.1.8 Results from 0.90in Oil Test ...................................................................................................... 38 3.1.9 Results from 0.95in Oil Test ...................................................................................................... 40 3.1.10 Results from 1.0in Oil Test ...................................................................................................... 42 3.1.11 Rotational Velocity Results ..................................................................................................... 44 3.1.12 Turbine Power Results ............................................................................................................. 46 3.1.13 Turbine Efficiency Results ....................................................................................................... 48

3.2 Wind Tunnel Tests with Torque Meter ............................................................................................. 49

3.3 Out of Wind Tunnel Test with Torque Meter ................................................................................... 51

3.3.1 Fan 12in from Turbine ............................................................................................................... 52 3.3.2 Fan 24in from Turbine. .............................................................................................................. 55

3.4 Conclusions ....................................................................................................................................... 58

3.5 Further Investigations ....................................................................................................................... 59

Works Cited ................................................................................................................................................ 61 Appendix A: Technical Drawings of Turbine ............................................................................................. 62 Appendix B: Raw Data ............................................................................................................................... 67 Appendix C: Calibration Information ......................................................................................................... 88

vi

List of Figures

Figure 1-1: Figure 3 from Darrius' Patent for his Turbine. (1) ..................................................................... 2

Figure 2-1: Exploded View of Turbine Assembly ........................................................................................ 7

Figure 2-2: Flange Design ............................................................................................................................ 9

Figure 2-3: Spoke Arm Design ..................................................................................................................... 9

Figure 2-4: NACA0018 Airfoil Profile ....................................................................................................... 10

Figure 2-5: Top View of Turbine Blade ..................................................................................................... 11

Figure 2-6: Side View of Turbine Blade ..................................................................................................... 11

Figure 2-7: Blade Half ................................................................................................................................ 12

Figure 2-8: Himmelstein Torque Meter ...................................................................................................... 13

Figure 2-9: LED Tachometer ...................................................................................................................... 14

Figure 2-10: Generator ................................................................................................................................ 15

Figure 2-11: Kestrel Wind Meter ................................................................................................................ 16

Figure 2-12: Test Chamber Layout, Top Down View and Side View ........................................................ 17

Figure 2-13: Torque Meter Configuration .................................................................................................. 18

Figure 2-14: Generator Set Up .................................................................................................................... 18

Figure 2-15: Out of Wind Tunnel Set Up ................................................................................................... 20

Figure 3-1: Rotational Velocity at 0.55in Oil ............................................................................................. 24

Figure 3-2: Output Power at 0.55in Oil ...................................................................................................... 25

Figure 3-3: Efficiency at 0.55in Oil ............................................................................................................ 25

Figure 3-4: Rotational Velocity at 0.6in Oil ............................................................................................... 26

Figure 3-5: Output Power at 0.6in Oil ........................................................................................................ 27

Figure 3-6: Efficiency at 0.6in Oil .............................................................................................................. 27



vii





Figure 3-13: Rotational Velocity at 0.75in Oil ........................................................................................... 32

Figure 3-14: Output Power at 0.75in Oil .................................................................................................... 33

Figure 3-15: Efficiency at 0.75in Oil .......................................................................................................... 33













Figure 3-28: Rotational Velocity at 1in Oil ................................................................................................ 42

Figure 3-29: Output Power at 1in Oil ......................................................................................................... 43

Figure 3-30: Efficiency at 1in Oil ............................................................................................................... 43

Figure 3-31: Rotational Velocity of the Turbine Across all Wind Velocities. ........................................... 44

Figure 3-32: Percent Error .......................................................................................................................... 45

Figure 3-33: Output Power from Generator and Air Power ....................................................................... 46

Figure 3-34: Output Power Error ................................................................................................................ 47

viii

Figure 3-35: Efficiency ............................................................................................................................... 48

Figure 3-36: Output Power of Turbine using the Torque Meter and Generator ......................................... 50

Figure 3-37: Rotational Velocity, Torque Meter vs. Generator .................................................................. 51

Figure 3-38: Torque from Tests Taken with Fan 12in from Turbine.......................................................... 52

Figure 3-39: Rotational Velocity Taken from Tests with Fan 12in from Turbine ...................................... 53

Figure 3-40: Output Power Calculated from Tests Taken with Fan 12in from Turbine ............................. 54

Figure 3-41: Efficiency Calculated from Tests Taken with Fan 12in from Turbine .................................. 54

Figure 3-42: Torque Taken from Tests with Fan 24in from Turbine.......................................................... 55

Figure 3-43: Rotational Velocity from Tests Taken with Fan 24in from Turbine ...................................... 56

Figure 3-44: Output Power Calculated from Tests Taken with Fan 24in from Turbine ............................. 57

Figure 3-45: Efficiency Calculated from Tests Taken with Fan 24in from Turbine .................................. 57

Figure A-1: Dimensioned Drawing for Turbine Shaft ................................................................................ 62

Figure A-2: Dimensioned Drawing of the Flanged Shaft Mount for the Turbine ...................................... 63

Figure A-3: Dimensioned Drawing of the Spoked Arm Wheel for the Turbine ......................................... 64

Figure A-4: Dimensioned Drawing of the Top Half of the Turbine Blade ................................................. 65

Figure A-5: Dimensioned Drawing of Bottom Half of the Turbine Blade ................................................. 66

Figure C-1: Torque Meter Calibration Sheet .............................................................................................. 88

Figure C-2: Torque Meter Spec Sheet ........................................................................................................ 89

Figure C-3: Tachometer Spec Sheet Side 1 ................................................................................................ 90

Figure C-4: Tachometer Spec Sheet Side 2 ................................................................................................ 91

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List of Tables

Table 2-1: Expected Torque Values ............................................................................................................ 12

Table 2-2: Wind Meter Calibration at 0.85in Oil ........................................................................................ 21

Table 3-1: Approximate Air Velocities in m/s ............................................................................................ 23

Table B-1: In Wind Tunnel with Generator, 0.55in Oil .............................................................................. 67

Table B-2: In Wind Tunnel with Generator, 0.6in Oil ................................................................................ 68


Table B-4: In Wind Tunnel with Generator, 0.7in Oil ................................................................................ 70


Table B-6: In Wind Tunnel with Generator at 0.8in Oil ............................................................................. 72

Table B-7: In Wind Tunnel with Generator at 0.85in Oil ........................................................................... 73

Table B-8: In Wind Tunnel with Generator at 0.9in Oil ............................................................................. 74

Table B-9: In Wind Tunnel with Generator at 0.95in Oil ........................................................................... 75

Table B-10: In Wind Tunnel with Generator at 1in Oil .............................................................................. 76

Table B-11: In Wind Tunnel with Generator Averages .............................................................................. 77

Table B-12: In Wind Tunnel with Torque Meter, Test 1 ............................................................................ 77



Table B-15: Out of Wind Tunnel with Torque Meter at 12in, Test 1 ......................................................... 80







x


Table C-1: Wind Meter Calibration at 0.425in Oil ..................................................................................... 92

Table C-2: Wind Meter Calibration at 0.5in Oil ......................................................................................... 93

Table C-3: Wind Meter Calibration at 0.65in Oil ....................................................................................... 94

xi

Nomenclature

APr: Projected area of the turbine

I: Current

P: Pressure

Patm: Atmospheric Pressure

PT: Power from Turbine

PW: Wind Power

R: Resistance

T: Torque

V: Voltage

VW: Wind Velocity

P: Pressure Difference

: Efficiency

: Air Denisty

: Rotational Velocity

1

Chapter 1

1.1 Introduction

Wind turbines are a growing area of interest in the energy market. With the push for the development of

green energy sources to reduce our dependence on fossil fuels such as coal, natural gas and oil, major

developments in the area of wind energy have been made in recent years. Many of the more well known

applications for wind energy are for large scale electric generation, with the commonly seen three bladed

turbines that can be seen in many windy areas. However, these types of turbines are not suited for

applications where the turbine needs to be portable or operate in low air speed areas.

Professor Alexander Gorlov developed a helical turbine designed for low fluid flow rates in the 1990s. It

was initially developed for use in water, either in a slow river or as a tidal generator. The turbine, which

uses a vertical axis configuration, has three blades that are swept along a helical path. With this

configuration, the turbine will always rotate in the same direction, regardless of the direction of the fluid

flow. With its small size and intended use for low flow situations, Gorlovs helical turbine is a prime

candidate to fill the need for a portable wind turbine.

The efficiency of a turbine, the ratio of the output electrical power compared to the input wind power, is

often used to determine how effective a given design is. The wind power can be determined using the

projection area of the turbine and wind velocity, in the equation

PW=0.5APrV3W

2

The efficiency of the turbine is defined as follows

=PT/PW

1.2 Literature Review

Gorlovs helical turbine is based off the Darrius turbine which was invented in 1926 by G.J.M. Darrius

and was patented in the US in 1931 (1). Darrius turbine is commonly seen with semi-circular blades

with an airfoil cross section spaced evenly around then shaft with the ends of the blades meeting near

each end of the shaft. A drawing of this common configuration, taken from his patent, can be seen below

in Figure 1-1. In his patent, Darrius claims that his design is an improvement over previous transverse

axis designs because his blades use airfoils which offer minimal resistance to forward movement in the

fluid and thus converting the maximum amount of available energy in the fluid to usable energy by way

of the shaft.

Figure 1-1: Figure 3 from Darrius' Patent for his Turbine. (1)

In his paper on the Limits of the Turbine Efficiency for Free Fluid Flow, Dr. Gorlov points out a

weakness in Darrius design. He states that due to the vibrations cause by the blades changing their angle

of attack during the rotation of the turbine, the turbine is prone to fatigue failure in its parts or joints (2).

3

Another invention that provided influence to Gorlovs design was a water wheel invented in 1902 by

Austrian Gustav Marburg. While Marburgs claims and focus are on methods of allowing the water

wheel to split, allowing a ship to pass through, it is stated that the blades have a spiral or helical turn to

render them more effective (3). Unlike Darrius turbine, the blades on Marburgs water wheel are

designed to harness the energy of the fluid through resistance, as opposed to lift. Gorlovs turbine

combines the use of airfoils on a transverse axis turbine with the helical path inspired by the drawings of

Marburgs water wheel.

Dr. Gorlov has filed for two patents for his turbine. His turbine was first patented in 1995 and claimed to

be a turbine with transverse airfoil blades in a helical configuration such that a portion of the blades were

always perpendicular to the flow, maintaining maximum thrust and a constant rotational velocity (4). In

the patent, hydro-pneumatic, hydro, wind and wave power systems are mentioned as sources of fluid flow

suitable for this design. Furthermore, there are statements suggesting that for gas turbine applications

under a low head pressure flow, the turbine can achieve similar rotational velocities to conventional

industrial generators, but with a higher efficiency.

The other patent filed for Gorlovs turbine is designed to protect additional uses for the technology that

were not originally covered in the first filing. The focus of the second patent is for using the turbine to

directly drive a propulsion system (5). This patent shows the versatility of the devise and its applications.

Aside from directly driving a propulsion device, uses such as lift and lowering objects in a fluid are cited

as well.

4

Dr. Gorlov also describes the advantages of his turbine in papers he published detailing some of his

experimental results. In a paper published around the same time his patent on the turbine was granted,

Dr. Gorlov describes the design in detail and results from tests he conducted. Among his claims and

descriptions, he states that the power output will increase with the diameter of the turbine while the flow,

the size and the shape of the blades remains the same (6). The paper also lists the results of two

investigations. In all three, the helical turbine was compared to a Darrius type turbine.

For the first investigation, the turbines were tested in conditions where there was a significant difference

in elevation across the turbine. For that test, the Gorlov turbine was found to be 27 percent more

efficient and to have a rotational velocity 41 percent faster than the Darrius turbine. The second

investigation concerned the two turbines where they were only the velocity head was being extracted by

the turbine. In this case, the Gorlov turbine was found to be 33 percent more efficient and 27 percent

faster than the Darrius type. Dr. Gorlov goes on to claim that in low flow conditions that his turbine is 95

percent more efficient and 49 percent faster than Darrius (6).

In Gorban et al., the turbines unconstrained performance is claimed to be 35 percent (2). The paper itself

focuses on mathematical models used to compute the performance of the turbine in a free flow situation.

The maximal efficiency obtained from these calculations was 0.30113 and this is the number that formed

the basis of my assumptions when selecting the instrumentation used for my investigations.

In a paper written by Howell et al., a small Darrius type turbine was tested in a wind tunnel and compared

to results from a computational model run in fluent. The primary purpose of this investigation was to

verify the computational model and thus the turbine tested wasnt designed to necessarily the most

5

efficient, but to provide results that would be easy to measure, given their size constraints (7). The results

illustrate the pulsating nature of the Darrius type turbine as described by Dr. Gorlov in his papers and

patents regarding his helical turbine. The paper also concludes that the computational model and the

physical tests were in reasonably good agreement, considering the errors and uncertainties involved in

both the physical test and the computational model.

In an article that appeared in the March 2009 issue of Environmental Engineering, author Niel Wilks

gives an overview of research that was being conducted at the time exploring the noise of vertical axis

turbines. He found that researchers were finding that turbines that follow the vertical or transverse axis

design are quieter than the horizontal axis counterparts (8).

Steven Peace, in an article that appeared in the June 2004 issue of ASMEs Mechanical Engineering,

argues that the future of wind turbines is with vertical axis designs, which the Darrius and Gorlov turbines

both fall under. Peace argues that vertical axis turbines have fewer limitations than horizontal turbines

and thus can be built to have larger swept areas and take advantage of larger input powers (9).

6

Chapter 2

2.1 Overview of Experiment

The goal of the experiment was to test a helical turbine in a controlled environment, measure the output

power and compare that with the available wind power to find the efficiency of the turbine. To do this,

two methods of measuring the turbines power were employed. The first consisted of using a torque meter

to determine the output torque and a tachometer to measure the rotational velocity, in revolutions per

second, of the turbine. The power would be calculated by the following relationship.

PT=2T

The second method used to determine the output power was as small generator powering a small resistor

circuit. Using Ohms Law,

V=IR

And the electrical power relationship,

PT=VI

The output power could be determined.

PT=V2/R

To calculate the air power over the projected area of the turbine, the air velocity was required. To

measure the air velocity in the wind tunnel a pitot tube attached to an oil manometer was used. For tests

done outside the wind tunnel, a hand held wind meter was used.

7

2.2 Design and Construction of the Turbine

2.2.1 Overview of Design

The turbine used for the experiments had to fit several criteria. The primary concern was making the

turbine small enough to fit into the wind tunnel in Northeasterns Richards Hall lab. The cross sectional

area of the test chamber on this wind tunnel perpendicular to the air flow measures 18.5 inches wide by

14 inches tall. Furthermore, the opening in the side of the test chamber that I would use to put the turbine

in measured 12 inches in diameter, so the turbine would also have to fit through that hole. With those

constraints and allowing for clearance between the turbine and the walls to reduce their effects on the

turbines performance, a projected area of 14 inches wide and 10 inches tall was settled on. An exploded

view of the assembly can be seen below in Figure 2-1.

Figure 2-1: Exploded View of Turbine Assembly

The two other main concerns were cost and weight. Due to the relatively small sized of the turbine, I

wanted to keep the turbine light to reduce losses and to use materials that were inexpensive. To

accomplish this, the turbine was constructed using plastics for the spoke arms and blades, aluminum for

8

the flanges and steel for the shaft. All of the solid models and drawings required for the production of

the turbine were created using SolidWorks.

2.2.2 Shaft Design

The shaft of the turbine consists of a single two foot length of steel measuring 3/8ths of an inch in

diameter. The use of steel over a lighter metal such as aluminum was based on the availability of

materials on McMaster-Carr where I sourced many of the materials and parts I needed to purchase. The

steel rod that was purchased for the shaft had a straightness tolerance of 0.05 inches where none of the

aluminum rods had a tolerance given.

2.2.3 Flange Design

The flanges, as shown in Figure 2-2, are used to attach the spoke arms to the shaft were machined out of

aluminum. The primary reason for these flanges being separate pieces instead of being part of the spoke

arm was to reduce the amount of material required. The flanges have three bolt holes to attach them to

the spoke arm and a single threaded hole for a set screw to secure them along with the spoke arm to the

shaft.

9

Figure 2-2: Flange Design

2.2.4 Spoke Arm Design

The spoke arm component, shown in Figure 2-3, has three arms extending from the central hub of the part

with extended sections at the end of the arms to attach the turbine blades. The leading edges of the arms

were also rounded to reduce the drag of the arms. For material, inch polycarbonate was chosen and the

parts were machined using a CNC machine.

Figure 2-3: Spoke Arm Design

10

2.2.5 Blade Design

The turbine blades are the most important part of this design. They are 14 inches long and follow a

helical path with a 5 inch radius over a 60 degree arc. The cross section is a standard NACA 0018 air foil

with a 1.5 inch chord. Since the airfoil is symmetric along the chord, the mean camber line follows the

chord. The helical path that the blade follows is drawn along the midpoint of the camber line and the

blade is set at a 0 degree angle of attack. The profile of the airfoil is shown in Figure 2-4.

Figure 2-4: NACA0018 Airfoil Profile

The blades were produced using a 3D printer that built the blades up a layer at a time with ABS plastic.

Due to the size constraints of the printer, the blades had to be cut in half and then assembled. The

assembly was done with a combination of plastic cement and pins to strengthen the joint. Additionally,

the joint was cut in a step shape to increase the surface area for bonding. While the glue and pins created

a strong joint, the bending stresses on the blades during operation would be centered on the joint area due

to the distance from the supports. The blades were further reinforced with fiber glass sleeves and epoxy,

resulting in a stiff blade that showed no visible deformation during testing.

11

Figure 2-5: Top View of Turbine Blade

Figure 2-6: Side View of Turbine Blade

Figures 2-5 and 2-6 show the top and side views of the turbine respectively. The top view illustrates the

arc of the helix that the blade follows while the side view shows the angle and the location of the join

where the two blade halves meet. The pitch and radius of the helix was determined by the projected area

of the turbine, which is the area in which the flow of the fluid interacts with the turbine. This area is the

determined by the length and diameter of the turbine, in this case being 140in2. Figure 2-7 shows a close

up of a single blade half, detailing the step design of the cut.

12

Figure 2-7: Blade Half

2.3 Selection of Instrumentation

2.3.1 Torque Meter

The torque meter selected for the testing was the Himmelstein model MCRT-48201V(25-0) (shown in

Figure 2-8). The meter is designed for a maximum of 2.82Nm of torque and was selected using an

expected power output based on the efficiency claims made by Professor Gorlov.

Table 2-1: Expected Torque Values

Air

Velocity

Rotational

Velocity

Air

Power

Expected

Efficiency

Expected

Output

Expected

Torque

(m/s) (RPM) (W) (W) (Nm)

5 250 6.692 0.3 2.008 0.077

6 260 11.564 0.3 3.469 0.127

7 270 18.363 0.3 5.509 0.195

8 280 27.411 0.3 8.223 0.280

9 290 39.028 0.3 11.708 0.386

10 300 53.536 0.3 16.061 0.511

11 310 71.257 0.3 21.377 0.659

12 320 92.511 0.3 27.753 0.828

13 330 117.619 0.3 35.286 1.021

14 340 146.904 0.3 44.071 1.238

15 350 180.685 0.3 54.206 1.479

13

As shown in Table 2-1, the expected torque output ranges from 0.077Nm to 1.479Nm depending on the

air velocity. The rotational velocities used were very rough estimates, since there were no previous tests

of this turbine conducted in air to base them on. The expected torque ranges up to around half of the

maximum torque the meter could handle. To get a torque meter with a lower maximum torque would

have required going to their low range line of meters, which were considerably more expensive than

meter used. Even then, the highest capacity of them, the 2.825Nm model, would have to have been

chosen, since the next size down had a maximum torque rating of 1.412Nm, which is lower than the

maximum torque expected.

Figure 2-8: Himmelstein Torque Meter

The Himmelstein torque meter operates by measuring the change in resistance of strain gauges applied to

the shaft of the meter. The meter comes with software for use with the RS-232 output, or the output can

be read as analog with either a 5V or 10V signal. The computer software will convert the voltage

14

output into units chosen by the user. It also has options to record the data as well as tare and calibrate the

meter.

2.3.2 Tachometer

To measure the rotational velocity of the turbine, an LED tachometer was chosen. The device operates by

illuminating an LED and sends an electronic pulse every time the light from the LED is reflected back

onto the photo sensor. The pulses were counted and displayed in Hz on an oscilloscope.

Figure 2-9: LED Tachometer

Since a piece of the reflective material was placed on each blade, the oscilloscope will show three pulses

per revolution of the turbine (RPS times 3).

2.3.3 Generator

For the direct electrical power measurements, a small bicycle generator was used. The generator chosen

was rated at 3 Watts and 6V, due to early test results showing poor performance. The generator was

connected to power a simple circuit consisting of a 10 ohm resistor. The voltage drop across the resistor

was measured to calculate the power.

15

Figure 2-10: Generator

2.3.4 Pitot Tube and Manometer

To measure the air velocity in the wind tunnel, a pitot tube connected to a manometer. The manometer

used consists of a vertical tube and a reservoir containing oil with a specific gravity of 0.826. Behind the

tube is a ruler in inches that can be moved to zero the manometer. The top of the manometer tube is open

to the atmosphere, so the pressure difference read is,

P = |P - Patm|

2.3.5 Wind Meter

To measure the air velocity when testing outside the wind tunnel, a Kestrel 1000 Wind Meter was used.

This meter uses an impeller mounted on the unit to measure the air velocity, which is displayed digitally

on a screen in units of the users choosing. To get a reading, the user must simply hold the meter in the

flow and read the output.

16

Figure 2-11: Kestrel Wind Meter

2.4 Test Setup and Procedure

2.4.1 Layout of the Test Chamber

The test chamber of the wind tunnel is 23 inches from entrance to exit, 18.5 inches wide and 14 inches

tall. In each corner there is a curved piece of plastic that serves as a diffuser for the two placed near the

entrance and as a nozzle for the two placed near the exit of the test chamber. On the left side of the

chamber when facing the direction of the airflow, there is a small hole cut into the wall which is covered

by a plastic plate from the outside. One of the bearings for the turbine was inserted into the plate. The

other bearing was inserted into the door panel that covers the much larger hole cut into the right side of

the test chamber. Along the top of the chamber is a long cut out for the pitot tube assembly, which is on a

track mechanism that allows the pitot tube to be positioned anywhere along the length of the chamber at

almost any height. The tube is limited, however, to the center of the width. In the center of the bottom

plate, there is a small hole, into which the LED tachometer was mounted, pointing directly up. An

overhead view of the test chamber with its inlet, outlet, diffuser and nozzle, and a side view can be seen in

Figure 2-12.

17

Figure 2-12: Test Chamber Layout, Top Down View and Side View

Outside the test chamber a tripod with a bracket for mounting the torque meter was positioned in such a

way that when the torque meter was mounted on the bracket, the shaft of the torque meter would be in

line with the shaft of the turbine. For the tests involving the generator, the bracket and tripod was used

along with a block of wood and some nylon cord to secure the generator in place.

2.4.2 Wind Tunnel Tests

For the wind tunnel tests, the turbine is supported on each end by bearings set into the walls of the wind

tunnel. The pitot tube was positioned in front of the turbine in the center of the plane perpendicular to the

air flow. Reflective tape was placed on the blades of the turbine and the tachometer was mounted in a

hole on the bottom of the test chamber, pointing up at the turbine.

For the measurements taken with the torque meter, the meter was mounted on a tripod and coupled to the

shaft of the turbine and a 50g weight was hung over a pulley placed on the torque meters shaft to provide

some resistance. Figure 2-13 shows the turbine in the wind tunnel with the torque meter

tripod. Also visible is the LED tachometer extending from the bottom of the test chamber

Figure

For the measurements taken with the generator,

directly to the shaft of the turbine. The 10 ohm resistor was

the probes from the oscilloscope where attached on either side of the resistor.

18

shows the turbine in the wind tunnel with the torque meter

tripod. Also visible is the LED tachometer extending from the bottom of the test chamber

Figure 2-13: Torque Meter Configuration

For the measurements taken with the generator, as can be seen in Figure 2-14, the generator was coupled

directly to the shaft of the turbine. The 10 ohm resistor was connected in a circuit with the generator and

the probes from the oscilloscope where attached on either side of the resistor.

Figure 2-14: Generator Set Up

shows the turbine in the wind tunnel with the torque meter mounted on the

tripod. Also visible is the LED tachometer extending from the bottom of the test chamber.

the generator was coupled

connected in a circuit with the generator and

19

For the generator tests, the air flow in the wind tunnel was set to a steady velocity and the system was

allowed to come to a steady state. Once this state was reached, ten readings of the air velocity, rotational

velocity and output torque or voltage were taken with 3 minutes in between each reading. Also noted was

the ambient temperature and atmospheric pressure at the beginning of the test. This was repeated for

multiple air velocities.

For the tests with the torque meter, only a few ramp ups were performed before it was concluded that the

generator was going to yield better results in the wind tunnel. The ramp ups were chosen for these tests

due to the observation that for every test, the tare value to zero the torque meter was different and the

output of the torque meter was different, even for the same settings. For the ramps, the test was started at

a low air velocity and the turbine was allowed to stabilize. Once it reached a steady rotational velocity, a

reading was taken and the air velocity was then increased to the next air velocity and the turbine was

allowed to stabilize again.

2.4.3 Out of Wind Tunnel Tests

For the tests outside of the wind tunnel, the turbine was mounted between two tables of equal heights with

the bearings set into blocks of wood. The tachometer was mounted to the top of one of the blocks and

reflective tape was placed on the spoke arms of the turbine. For this setup, only the torque meter was

used and it was coupled directly to the turbine shaft with the same 20g weight over the pulley as the tests

inside the wind tunnel. The torque meter itself rested on the table used to support one of the mounting

blocks for the turbine. To provide air flow, a large fan was placed in front of the test rig and the handheld

wind meter was used to take velocity readings. The set up is illustrated in Figure 2-15.

20

Figure 2-15: Out of Wind Tunnel Set Up

Similar to the in wind tunnel tests, the system was allowed to stabilize and then 10 readings were taken

with an interval of 3 minutes between each reading. Since the fan used to provide the air flow only had

one speed, the test was repeated with the fan at varying distances from the turbine. The turbine was tested

with the fan 12in and 24in, measured from the screen on the front of the fan to the shaft of the turbine,

away.

2.4.4 Calibration Check on Handheld Wind Meter

Since the handheld wind meter used for the tests outside the wind tunnel didnt come with any calibration

documentation, its accuracy was tested by comparing readings taken from it and the manometer at the

same time in the same flow. To do this, the wind meter was mounted in the wind tunnel with the impeller

as close to the pitot tube as possible. They were positioned in the center of the wind tunnel. Multiple

readings were taken at each air velocity over a period of time.

21

Table 2-2: Wind Meter Calibration at 0.85in Oil

Temperature 26

Atmospheric Pressure (in Hg) 29.97

SG Oil 0.826

Air Density (kg/m^3) 1.180303

Reading Wind Meter Manometer M. Speed Percent

# m/s (in Oil) (m/s) Error

1 17.2 0.85 17.217 0.101

2 17.3 0.85 17.217 0.479

3 17.3 0.85 17.217 0.479

4 17.3 0.85 17.217 0.479

5 17.2 0.85 17.217 0.101

6 17.2 0.85 17.217 0.101

7 17.3 0.85 17.217 0.479

8 17.3 0.85 17.217 0.479

9 17.3 0.85 17.217 0.479

10 17.2 0.85 17.217 0.101

Average 17.26 0.85 17.217 0.328

The check was done at four different air speeds and it was found that the hand held wind meter did give

accurate readings. Table 2-2 shows the results from the test done at 0.85in oil in the manometer. The rest

of the calibration data can be seen in Appendix C. This test showed the smallest difference between the

manometer and the wind meter of the four tests performed. In this case the average error was 0.328%.

The error was calculated using the following equation.

%Error=|(Wind Meter Manometer)/Manometer|*100

The main cause for the error was the resolution of the manometer which only had gradations in .1in

intervals. This meant that the height of the oil in the tube could only be read to the nearest .05in. With

22

that limitation in mind, the air speed shown on the wind meter was close to the speed calculated from the

manometer in all four cases.

23

Chapter 3

For the tests conducted in the wind tunnel, the air velocity is referred to in terms of inches of manometer

oil. Below, on Table 3-1, is an approximate conversion from in Oil to m/s. For this table, the temperature

and barometric pressure were assumed. In the actual tests, the values of the ambient temperature and

barometric pressure were recorded for use in calculating the specific air velocity and power for that test.

Table 3-1 is for reference to give an approximate idea of the airs velocity in familiar units.

Table 3-1: Approximate Air Velocities in m/s

Manometer Temperature Barometer

Air

Density

Air

Velocity

in Oil C in Hg kg/m^3 m/s

0.55 25 29.9 1.181 13.843

0.6 25 29.9 1.181 14.458

0.65 25 29.9 1.181 15.049

0.7 25 29.9 1.181 15.617

0.75 25 29.9 1.181 16.165

0.8 25 29.9 1.181 16.695

0.85 25 29.9 1.181 17.209

0.9 25 29.9 1.181 17.708

0.95 25 29.9 1.181 18.193

1 25 29.9 1.181 18.666

3.1 Wind Tunnel Tests with Generator

A majority of the testing in the wind tunnel was performed using the generator to measure the output

power. The main tests done using the generator consisted of taking multiple readings at the same air

speed. This was done at a manometer reading of 0.55in to 1in in 0.05in intervals with 10 readings taken

at each. The readings were then averaged for each interval. The tabulated raw data and calculated values

for output power and efficiency can be found in Appendix B.

24

3.1.1 Results from 0.55in Oil Test

Figure 3-1: Rotational Velocity at 0.55in Oil

The results from the test taken at 0.55in Oil in the manometer can be seen in Figures 3-1, 3-2 and 3-3.

The turbine rotated with a velocity around 3.36 revolutions per second (RPS), which was not a high

enough rate to get a meaningful voltage out of the generator used, which the output power and efficiency

results clearly show. The primary purpose of this test is that it shows that the generator needs to be

turning at a minimum rate that lies between the results of this test and the test performed at 0.60in Oil.

3.25

3.3

3.35

3.4

3.45

3.5

1 2 3 4 5 6 7 8 9 10

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Reading Number

Rotational Velocity at 0.55in Oil, Generator

Rotational Velocity

Average Velocity

25

Figure 3-2: Output Power at 0.55in Oil

Figure 3-3: Efficiency at 0.55in Oil

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number

Output Power at 0.55in Oil, Generator

Output Power

Average Output

0

0.00005

0.0001

0.00015

0.0002

0.00025

0.0003

0.00035

0.0004

0.00045

0.0005

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Efficiency at 0.55in Oil, Generator

Efficiency

Average Efficiency

26



The rotational velocity at 0.6in Oil, as shown in Figure 3-4, was slightly less than 2RPS faster than it was

at 0.55in Oil. This rotational velocity surpassed the minimum needed to be able to get the generator to

create a current. The output power, shown in Figure 3-5 was very stable, with only two points differing

from the rest. As such, the efficiency, shown in Figure 3-6 was in general close to its average for the test

as well.

5

5.05

5.1

5.15

5.2

5.25

5.3

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational

Velocity

Average

Velocity

27



0.41

0.415

0.42

0.425

0.43

0.435

0.44

0.445

0.45

0.455

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number


Output Power

Average Output

0.255

0.26

0.265

0.27

0.275

0.28

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

28



The test conducted with the air velocity set at 0.65in Oil was, like the test conducted at 0.6in Oil,

relatively stable in terms of rotational velocity, output power and efficiency. The variations of the

rotational velocity, output power and efficiency as compared to their average over the whole test can be

seen in Figures 3-7, 3-8 and 3-9 respectively.

6.05

6.1

6.15

6.2

6.25

6.3

6.35

6.4

1 2 3 4 5 6 7 8 9 10

Ro

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Reading Number


Rotational Velocity

Average Velocity

29



0.59

0.595

0.6

0.605

0.61

0.615

0.62

0.625

0.63

0.635

0.64

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number


Output Power

Average Output

0.325

0.33

0.335

0.34

0.345

0.35

0.355

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

30



The test conducted at an air velocity of 0.7in Oil was relatively stable as well. The power measurements

only showed two points that differed from the rest while the rotational velocity measurements showed the

turbine maintaining a relatively consistent velocity. Figures 3-10, 3-11 and 3-12 show the results from

this test, comparing the individual readings to the average values of that test.

6.6

6.65

6.7

6.75

6.8

6.85

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational Velocity

Average Velocity

31



0.67

0.68

0.69

0.7

0.71

0.72

0.73

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number


Output Power

Average Output

0.33

0.335

0.34

0.345

0.35

0.355

0.36

1 2 3 4 5 6 7 8 9 10

Eff

cie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

32



Unlike the previous few tests, the test at 0.75in Oil showed more variation in the results. Throughout the

test, the rotational velocity varied more than in previous tests, and going from the higher end of the range

down to the lower end of the range and then back up again. The output power and efficiency show

similar variation during the first half of the test before leveling off during the second half. This variation

shows a weakness with the timing of the readings. With the readings spaced out as they were, there was

the chance that the point taken at the time of the reading was not indicative of the actual performance over

all.

The results from this can be seen in Figures 3-13, 3-14 and 3-15.

6.82

6.84

6.86

6.88

6.9

6.92

6.94

6.96

6.98

7

7.02

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational Velocity

Average Velocity

33



0.73

0.74

0.75

0.76

0.77

0.78

0.79

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number

Ouptut Power at 0.75in Oil, Generator

Output Power

Average Output

0.325

0.33

0.335

0.34

0.345

0.35

0.355

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Effciency at 0.75in Oil, Generator

Efficiency

Average Efficiency

34



Like the test performed at 0.8in Oil, the test at 0.85in oil showed more variation in the output power and

efficiency calculations than the earlier tests, though the rotational velocity was relatively consistent. The

test further illustrates the fluctuations in power output from the generator.

The results of the test can be seen in Figures 3-16, 3-17 and 3-18.

7.1

7.12

7.14

7.16

7.18

7.2

7.22

1 2 3 4 5 6 7 8 9 10

Ro

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Reading Number


Rotational Velocity

Average Velocity

35



0.8

0.81

0.82

0.83

0.84

0.85

0.86

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number


Output Power

Average Output

0.325

0.33

0.335

0.34

0.345

0.35

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

36



The test at an air velocity of 0.85in Oil turned out to be the most consistent in terms of power output, with

only one point differing from the others, right at the end of the test, as seen in Figure 3-20. The rotational

velocity, Figure 3-19, is like the other tests and shows some variation, due to the method the oscilloscope

uses to count the pulses from the tachometer and display the frequency of them. The calculated efficiency

for each reading can be seen in Figure 3-21.

7.35

7.4

7.45

7.5

7.55

7.6

7.65

7.7

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational Velocity

Average Velocity

37



0.94

0.95

0.96

0.97

0.98

0.99

1

1.01

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number


Output Power

Average Output

0.345

0.35

0.355

0.36

0.365

0.37

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

38



The rotational velocity, as seen in Figure 3-22, for the test conducted with an air velocity at 0.9in Oil

again displayed a range of values with a difference between the high and low value being around

0.16RPS. Like other tests, this can mostly be attributed to the oscilloscopes error. The power and

efficiency calculations show variability during the early readings of the test and then level off for the last

five readings, as shown in Figures 3-23 and 3-24. The power fluctuation covers a rather significant range,

considering the scale of the output. This could indicate that either the turbine or the generator with its

resistor reaching a limit in their performance.

8.14

8.16

8.18

8.2

8.22

8.24

8.26

8.28

8.3

8.32

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational Velocity

Average Velocity

39



0.94

0.96

0.98

1

1.02

1.04

1.06

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number


Output Power

Average Output

0.32

0.325

0.33

0.335

0.34

0.345

0.35

0.355

0.36

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Effciency at 0.9in Oil, Generator

Efficiency

Average Efficiency

40



At an air velocity of 0.95in, the rotational velocity, as seen in Figure 3-25, was less consistent than many

of the other tests conducted with this configuration. This observation goes over to the power and

efficiency results, shown in Figures 3-26 and 3-27 respectively, as well. The range that contains all of the

power calculations is almost as large as the range in the previous test.

8.7

8.75

8.8

8.85

8.9

8.95

9

9.05

1 2 3 4 5 6 7 8 9 10

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Reading Number


Rotational Velocity

Average Velocity

41



1.04

1.05

1.06

1.07

1.08

1.09

1.1

1.11

1.12

1.13

1.14

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number


Output Power

Average Output

0.325

0.33

0.335

0.34

0.345

0.35

0.355

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number


Efficiency

Average Efficiency

42


Figure 3-28: Rotational Velocity at 1in Oil

The final test with the generator was conducted at an air velocity of 1in Oil. In Figure 3-28, it shows that

the rotational velocity again has a wide range of variation, though on average is about the same as it was

in the tests conducted at 0.95in Oil. The output power and efficiency, shown in Figures 3-29 and 3-30

respectively, show similar averages to the 0.95in Oil test as well, though a much smaller range of

variation.

8.65

8.7

8.75

8.8

8.85

8.9

8.95

9

9.05

1 2 3 4 5 6 7 8 9 10

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Reading Number

Rotational Velocity at 1in Oil, Generator

Rotational Velocity

Average Velocity

43

Figure 3-29: Output Power at 1in Oil

Figure 3-30: Efficiency at 1in Oil

1.04

1.05

1.06

1.07

1.08

1.09

1.1

1.11

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

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(W)

Reading Number

Output Power at 1in Oil, Generator

Output Power

Average Output

0.302

0.304

0.306

0.308

0.31

0.312

0.314

0.316

0.318

0.32

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Efficiency at 1in Oil, Generator

Efficiency

Average Efficiency

44

3.1.11 Rotational Velocity Results

In general, the rotational velocity of the turbine rose as the air speed in the wind tunnel increased, though

the rate of increase was not constant and reached a plateau at 0.95in Oil. Figure 3-31 shows the averaged

rotational velocity from each wind velocity that the static test was conducted at.

Figure 3-31: Rotational Velocity of the Turbine Across all Wind Velocities.

At each speed however, there was some variation in rotational velocity over the course of a single test.

The percent error for each reading was determined by dividing the difference of the individual reading

and the average rotational velocity by the average rotational velocity. The average error ranged from an

average error of 0.433% at 0.8in Oil to 1.665% at 0.55in Oil. The error curve can be seen in Figure 3-32.

0

2

4

6

8

10

0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

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Wind Velocity (in Oil)

Rotational Velocity

Rotational Velocity

45

Figure 3-32: Percent Error

The primary source of the error seen in the rotational velocity is rounding errors made by the oscilloscope

used to read the output from the tachometer. When the oscilloscope is reading the rotational velocity, it

counts the number of pulses over a certain period of time and then divides that number by the time period

to give a reading in Hz. Depending on the time period used the number of pulses, even if they are

occurring at a regular rate, in that period may not be the same as the number of pulses in the previous time

period.

In the case of the higher error at the 0.55in Oil test point the turbine was observed to have an unstable

rotational velocity. If the air velocity in the wind tunnel was lower than 0.55in Oil, it was observed that

the turbines velocity would become visible more erratic as the air power to keep the turbine going in that

environment was just not there.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Av

era

ge

Pe

rce

nt

Err

or

(%)

Air Velocity (in Oil)

Rotational Velocity Error

Rotational Velocity

46

3.1.12 Turbine Power Results

The power readings from the generator were much more consistent, in that most readings on a given test

were the same with a few outliers, than the rotational velocity readings. The output power however, was

much lower than anticipated. With air power across the projected area of the turbine in excess of 300W at

the highest air velocity settings, the turbine put out just more than 1W in electrical power from the

generator. From initial assumptions, an output of 60W to 90W was expected at the top air velocities

based on the efficiency figures claimed by Professor Gorlov.

Figure 3-33: Output Power from Generator and Air Power

Figure 3-33 shows how the output power for the turbine changes as the air speed increases. As can be

seen, the air power increases following the path of a third order polynomial, which is based on how the air

power is calculated. It could be speculated that the output power would follow a similar path in an ideal

situation; however that is not the case here. Instead the output power follows a logarithmic patch,

reaching an asymptote at around 1W. The output for the first speed setting is omitted due to observation

that the rotational velocity at that setting was not enough to produce a meaningful voltage from the

generator.

0

50

100

150

200

250

300

350

400

0

0.15

0.3

0.45

0.6

0.75

0.9

1.05

1.2

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Air

Po

we

r (W

)

Ou

tpu

t P

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(W)


Output and Air Power

Output Power

Air Power

47

The error with respect to the average output at each point was higher on average than the error for the

rotational velocity. The highest error was at 0.55in Oil where the average error was 51.429%. This is an

outlier since the generator at this air velocity was showing virtually no voltage. Outliers aside, the error

ranged from 0.942% at 0.85in Oil at the low point to 3.826% at 0.9in Oil at the high point. For the tests

that had lower average error, the error tended to be caused by a couple points being either higher or lower

than the others while a significant majority of the points were the same.

The average error over all the air velocities tested at, excluding the test at 0.55in Oil can be seen in Figure

3-34.

Figure 3-34: Output Power Error

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Pe

rce

nt

Err

or

(%)


Output Power Error

Output Power Error

48

3.1.13 Turbine Efficiency Results

The turbine efficiency in these tests was poor, managing just over 0.35% at best. This is well below the

expected 25% efficiency. Since the efficiency is calculated from the output power of the turbine and

compare to the power of the air over the projected area of the turbine which is constant, the efficiency has

the same error as the output power. Like the output power, the efficiency at 0.55in Oil is an outlier due to

the fact that the generator used to measure the power was not producing a significant voltage at that

velocity.

Figure 3-35: Efficiency

Figure 3-35 shows how the efficiency changes as the air velocity increases. As it can be seen, the

efficiency stays around the .33% to .35% range and then drops off as the air velocity reaches 1in Oil.

This follows the observations gained from the output power readings where the output power stagnated

once the air velocity reached 0.95in Oil.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.6

0.6

5

0.7

0.7

5

0.8

0.8

5

0.9

0.9

5

1

Eff

icie

ncy

(%

)


Efficiency

Efficiency

49

3.2 Wind Tunnel Tests with Torque Meter

Much of the early testing of the turbine in the wind tunnel was performed with the torque meter. As the

results from the generator show, the turbine performed much worse than expected. With the early results

with the torque meter, it was unclear whether or not the turbine was really performing that poorly or if

there was a problem with the instrumentation. It was these initial tests that spurred the use of the

generator as a way to check that the torque was indeed operating correctly. The generator confirmed that

the turbine was not performing as expected, though it was observed that at the same air velocities, more

power was being generated when the generator was used than when the torque meter was used. On

comparing rotational velocity readings, it was found that the turbine turned significantly slower when the

torque meter was attached than when the generator was attached. Another issue that was observed was

that for each test, the tare value for the torque meter was significantly different.

The few tests that were run with the torque meter in the wind tunnel were done as ramps, where the test

was started at a low air velocity and it was then ramped up at set intervals, with data taken at each point.

This method was used due to the changing tare value for the torque meter. The raw data and calculated

properties can be found tabulated in Appendix B

50

Figure 3-36: Output Power of Turbine using the Torque Meter and Generator

Figure 3-36 shows that with the torque meter, the measured output power is only half of what was

measured using the generator. Also note that the output power for the -0.0181 tare run with the torque

meter is noticeably higher than the -0.0143 and -0.0153 tare runs. In theory the output torque measured

should be roughly the same across all tests, since the tare sets the displayed value to zero before the test

begins. It was observed, however, the value of the tare was dependent, in some degree to the initial

position of the turbine, suggesting some imbalance either in the turbine or in the flexible coupler used to

couple the shafts to one another.

0

0.2

0.4

0.6

0.8

1

1.2

0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Ou

tpu

t P

ow

er

(W)


Output Power, Torque Meter vs. Generator

Tare: -0.0143

Tare: -0.0153

Tare: -0.0181

Generator

51

Figure 3-37: Rotational Velocity, Torque Meter vs. Generator

Figure 3-37 shows that with the torque meter in place, the turbine rotated at a much slower rate in the

wind tunnel than it did with the generator. This shows that there was significantly more resistance in the

torque meter set up than there was in the generator set up. Due to this, the data gathered from the

generator provides a much more accurate picture of what is going on.

3.3 Out of Wind Tunnel Test with Torque Meter

For the tests conducted outside the wind tunnel, the torque meter had to be used because the turbine did

not rotate at a high enough velocity to produce a measurable voltage drop across the resistor attached to

the generator. Like the tests using the torque meter conducted inside the wind tunnel, the varying tare

value caused some inconsistencies in the torque values read from the torque meter. However, the varying

0

1

2

3

4

5

6

7

8

9

10

0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Ro

tati

on

al

Ve

loci

ty (

RP

S)


Rotational Velocity, Torque Meter vs. Generator

Tare: -0.0143

Tare: -0.0153

Tare: -0.0181

Generator

52

rotational velocity given by the tachometer was the main source for the differences in the output power

shown.

3.3.1 Fan 12in from Turbine

The test was run four times with the fan placed 12in away from the turbine, with the torque meter being

zeroed at the beginning of each test. The measured air velocity was relatively consistent, ranging from

5m/s to 5.3m/s.

Figure 3-38: Torque from Tests Taken with Fan 12in from Turbine

Figure 3-38 shows how the torque varied with each test. The main correlation that can be derived is that

the torque values are dependent on the tare value of the torque meter at the time that the test was

performed. The reason the tare value has such a noticeable effect on the outcomes of these tests is due to

the extremely low output torques seen from this turbine. If the turbine was performing as expected, the

differences caused by the change in the tare would be a small percentage of the overall measured torque.

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

1 2 3 4 5 6 7 8 9 10

To

rqu

e (

Nm

)

Reading Number

Torque with Fan 12in from Turbine

Tare: -0.0136 Air: 5.2m/s

Tare: -0.0160 Air: 5.3m/s

Tare: -0.0166 Air: 5.2m/s

Tare: -0.0185 Air: 5m/s

53

Figure 3-39: Rotational Velocity Taken from Tests with Fan 12in from Turbine

Above in Figure 3-39, the rotational velocities measured in the tests can be seen. The rotational velocities

remained rather consistent across the tests which is expected, since the fan only had one speed setting and

remained in the same position for all four of the tests run.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1 2 3 4 5 6 7 8 9 10

Ro

tati

on

al

Ve

loci

ty (

RP

S)

Reading Number

Rotational Velocity with Fan 12in from Turbine

Tare: -0.0136 Air: 5.2m/s

Tare: -0.0160 Air: 5.3m/s

Tare: -0.0166 Air: 5.2m/s

Tare: -0.0185 Air: 5m/s

54

Figure 3-40: Output Power Calculated from Tests Taken with Fan 12in from Turbine

Figure 3-41: Efficiency Calculated from Tests Taken with Fan 12in from Turbine

0

0.005

0.01

0.015

0.02

0.025

0.03

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number

Output Power with Fan 12in from Turbine

Tare: -0.0136 Air: 5.2m/s

Tare: -0.0160 Air: 5.3m/s

Tare: -0.0166 Air:5.2m/s

Tare: -0.0185 Air: 5m/s

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Efficiency with Fan 12in from Turbine

Tare: -0.0136 Air: 5.2m/s

Tare: -0.0160 Air: 5.3m/s

Tare: -0.0166 Air: 5.2m/s

Tare: -0.0185 Air: 5m/s

55

The output power of the turbine in these tests can be seen in Figure 3-40 and the efficiency in Figure

3-41. Both calculated properties follow the same curves as they are directly related to one another.

However, the output power results appear closer to each other since they do not take into account the

different measured air velocities. In theory, the measured air velocity should have been the same for each

test. In practice, getting the wind meter in the same exact position for every test proved impossible.

Since the reading taken from the meter was dependent on its position for each test when the air velocity

reading was taken, the measured values differ somewhat.

3.3.2 Fan 24in from Turbine.

The second set of tests performed with the turbine outside the wind tunnel were done with the fan

positioned 24in from the turbine. The air velocity during these tests was only slightly lower than it was

with the fan 12in from the turbine with the velocity for these tests ranging from 4.9m/s to 5.1m/s.

Figure 3-42: Torque Taken from Tests with Fan 24in from Turbine

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

1 2 3 4 5 6 7 8 9 10

To

rqu

e (

Nm

)

Reading Number

Torque with Fan 24in from Turbine

Tare: -0.0134 Air: 5.1m/s

Tare: -0.0145 Air: 5m/s

Tare: -0.0171 Air: 5.1m/s

Tare: -0.0173 Air: 4.9m/s

56

Figure 3-42 shows the torque measured from each test across all ten readings for each. As the figure

shows, the torque for all four tests remained relatively stable for the duration of each test and like the

previous tests done at 12in varied from test to test based on the tare value.

Figure 3-43: Rotational Velocity from Tests Taken with Fan 24in from Turbine

The rotational velocity, shown in Figure 3-43 is not as consistent across the four tests at 24in as it was

across the four tests at 12in.

Both the output power and efficiency, shown in Figures 3-44 and 3-45, show a much larger spread than

the tests at 12in. This is mainly a result of the less consistent rotational velocities measured during these

tests.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2 3 4 5 6 7 8 9 10

Ro

tati

on

al

Ve

loci

ty (

RP

S)

Reading Number

Rotational Velocity with Fan 24in from Turbine

Tare: -0.0134 Air: 5.1m/s

Tare: -0.0145 Air: 5m/s

Tare: -0.0171 Air: 5.1m/s

Tare: -0.0173 Air: 4.9m/s

57

Figure 3-44: Output Power Calculated from Tests Taken with Fan 24in from Turbine

Figure 3-45: Efficiency Calculated from Tests Taken with Fan 24in from Turbine

0

0.005

0.01

0.015

0.02

0.025

1 2 3 4 5 6 7 8 9 10

Ou

tpu

t P

ow

er

(W)

Reading Number

Output Power with Fan 24in from Turbine

Tare: -0.0134 Air: 5.1m/s

Tare: -0.0145 Air: 5m/s

Tare: -0.0171 Air: 5.1m/s

Tare: -0.0173 Air: 4.9m/s

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1 2 3 4 5 6 7 8 9 10

Eff

icie

ncy

(%

)

Reading Number

Efficiency with Fan 24in from Turbine

Tare: -0.0134 Air: 5.1m/s

Tare: -0.0145 Air: 5m/s

Tare: -0.0171 Air: 5.1m/s

Tare: -0.0173 Air: 4.9m/s

58

3.4 Conclusions

Overall, the turbine did not perform anywhere near what was expected at the outset of this investigation.

Results of 25% to 30% efficient would have fallen right in line with the claims m

Documents

Efficiency Investigation of a Helical Turbine for Harvesting Wind