Fyp Intro

Design of Wells turbine for conversion of airflow energy for small scale power generation. By Nooha Bibi Wajiha Peerally

Submitted as partial fulfilment for the degree of B.Eng (Hons) Mechanical Engineering

University of Mauritius Faculty of Engineering Mechanical and Production Engineering Department

TABLE OF CONTENTS ABSTRACT ...................................................................................................................... i LIST OF ABBREVIATIONS .......................................................................................... ii NOTATIONS .................................................................................................................. iii Chapter 1 : INTRODUCTION ......................................................................................... 1 Background.................................................................................................................... 2 Sources of airflow for energy conversion using Wells turbine ..................................... 2 Wind energy .......................................................................................................... 2 Wave energy.......................................................................................................... 3 Turbines ......................................................................................................................... 4 Aim and Objectives........................................................................................................ 5

Chapter 2 : Literature Review .........................................Error! Bookmark not defined. 2.1.

Working principle of Wells turbine ................................ Error! Bookmark not defined.

2.2.

Types of Wells turbines .................................................. Error! Bookmark not defined.

2.3.

The design and performance variables .......................... Error! Bookmark not defined.

2.3.1

Speed of airstream ................................................. Error! Bookmark not defined.

2.3.2

Tip speed ratio, λtip ................................................. Error! Bookmark not defined.

2.3.3

Flow ratio................................................................ Error! Bookmark not defined.

2.3.4

Blade solidity, σ ...................................................... Error! Bookmark not defined.

2.3.5

The hub-tip ratio, h................................................. Error! Bookmark not defined.

2.3.6

Aspect Ratio............................................................ Error! Bookmark not defined.

2.3.7

The tip clearance .................................................... Error! Bookmark not defined.

2.3.8

The aerofoil profile and thickness ratio, τ .............. Error! Bookmark not defined.

2.3.9

The critical speed.................................................... Error! Bookmark not defined.

2.3.10

Blade Sweep angle, blade sweep, and blade skew Error! Bookmark not defined.

2.4

Turbine Performance ..................................................... Error! Bookmark not defined.

2.5

Cascade effect ................................................................ Error! Bookmark not defined.

2.6

Previous papers on improvement of Wells turbine ....... Error! Bookmark not defined.

2.7

Small-scale Wind Turbines with Added Shrouds............ Error! Bookmark not defined.

Chapter 3 : Methodology .................................................Error! Bookmark not defined.

3.1

Determining application of the device ........................... Error! Bookmark not defined.

3.2

Concept design ............................................................... Error! Bookmark not defined.

3.3

Detailed design ............................................................... Error! Bookmark not defined.

3.4

Design testing ................................................................. Error! Bookmark not defined.

3.5

Building and experimental testing of prototype ............ Error! Bookmark not defined.

Chapter 4 : Concept design..............................................Error! Bookmark not defined. 4.1

Mathematical model of Wells turbine ........................... Error! Bookmark not defined.

4.2

Design of turbine rotor blades ....................................... Error! Bookmark not defined.

4.2.1 Area ratio for the device and the turbine airfoil blades........ Error! Bookmark not defined. 4.2.2 3.5.

Radial Equilibrium Approach .................................. Error! Bookmark not defined.

Basic equations of motion of a rotating system............. Error! Bookmark not defined.

References .......................................................................Error! Bookmark not defined. Reference .........................................................................Error! Bookmark not defined.

LIST OF FIGURES Figure 1: Illustration of the project objectives. ................................................................ 5 Figure 2: Power conversion chain for the system ...........Error! Bookmark not defined. Figure 3: Outline of a Wells turbine (Raghunathan et al., 1982).Error! Bookmark not defined. Figure 4: Forces acting on an airfoil during compression.Error!

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not

defined. Figure 5: Forces acting on an airfoil during suction........Error! Bookmark not defined. Figure 6: Performance parameters of the Wells turbine ..Error! Bookmark not defined. Figure 7: Effect of flow ratio on pressure drop: R = 2.8 x 105, h = 0.62................. Error! Bookmark not defined. Figure 8: Effect of flow ratio on efficiency: R = 2.8 x l05, h = 0.62Error!

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not defined. Figure 9: Effect of solidity on the normalized values of pressure drop and efficiency profile (Raghunathan, 1989) ............................................Error! Bookmark not defined. Figure 10: Effect ' of hub-tip ratio on efficiency: NACA0021 profile (Raghunathan, 1983) .........................................................................................Error! Bookmark not defined. Figure 11: Effect of blade aspect ratio on efficiency and stall. NACA 0015, h=0.65-0.7 and R= 3×105 (Raghunathan, 1995) ................................Error! Bookmark not defined. Figure 12: Effect of tip clearance on time averaged efficiency (Raghunathan 1995). .........................................................................................Error! Bookmark not defined. Figure 13: 3D blade proposed by Takasaki et al. ............Error! Bookmark not defined. Figure 14: Representation of Blade sweep (Shehata et al, 2016)Error! Bookmark not defined. Figure 15: Skewed Wells turbine rotors (Starzmann and Carolus, 2013) ............... Error! Bookmark not defined.

Figure 16: Comparison between the optimal shape of the airfoil and the original profile NACA 2421 (Mohamed, 2008) .......................................Error! Bookmark not defined. Figure 17: experimental apparatus for performance test (Suzuki and Arakawa, 2008) .........................................................................................Error! Bookmark not defined. Figure 18: An initial design of diffuser modelled using CFD (Kishore, Coudron and Priya, 2013) ................................................................................Error! Bookmark not defined. Figure 19: Schematic of a wind turbine equipped with a flanged diffuser shroud. . Error! Bookmark not defined. Figure 20: Velocity vector at the inlet of the Wells turbineError!

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defined. Figure 21: Velocity vector at outlet of the Wells turbine Error! Bookmark not defined. Figure 22: Velocity vector at the inlet of the Wells turbineError!

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defined. Figure 23: Velocity vector at outlet of the Wells turbine Error! Bookmark not defined.

LIST OF TABLES Table 1: Summary of the existing Wells turbine projects (Shehata et al., 2016) .... Error! Bookmark not defined.

ACKNOWLEDGEMENT

PROJECT DECLARATION FORM

ABSTRACT

i

LIST OF ABBREVIATIONS

ii

NOTATIONS Quantity

Symbol

Units

Aerodynamic Efficiency

η

-

Angle of Absolute Velocity

β

Degrees

Angle of Attack

α

Degrees

Angular Velocity

ω

rad/s

Axial Force Coefficient

Cx

-

Axial Velocity

Vx

m/s

Blade Aspect Ratio

AR

-

Blade Circumferential Velocity

U

m/s

Blade Clearance at Tip

τc

m

Blade Height

l

m

Blade Thickness Ratio

τ

-

Chord Length

c

m

Circumferential Force Coefficient

Cθ

-

Circumferential Velocity

Vθ

m/s

Cross sectional area of the turbine

at

Density

ρ

kg/m3

Density of Air

ρa

kg/m3

iii

Drag Coefficient

Cd

-

Drag Force

D

N

Energy Dissipation Associated with Drag

Ed

J

Flow Rate

Q

m3/s

Flow Ratio

ϕ

-

Hub to Tip Ratio

h

-

Kinematic Viscosity of Air

υ

m2/s

Kinetic Energy at Exit Plane

Ek

J

Lift Coefficient

CL

-

Lift Force

L

N

Lift Force on Blades

L

N

Mach Number Relative to Blades

M

-

Non-Dimensional Pressure-Drop

p*

-

Number of Blades

N

-

Power Input

Wi

W

Pitch

t

Power Output

Wo

W

Pressure Coefficient

Cp

-

Pressure Drop across the Rotor

Δp

Pa

iv

Pressure head

H

m

Relative Velocity

w

m/s

Rotational Speed

n

rev/min

Rotor Swept Area

A

m2

Reynolds Number

R

-

Speed of of sound

a

m/s

Solidity Ratio

σ

-

Static Pressure

p

Pa

Tip Speed Ratio

λtip

-

Torque

T

Nm

Total Velocity

V

m/s

Turbine Hub Diameter

Dh

m

Turbine Tip Diameter

Dt

m

Turbine Tip Radius

Rt

m

Turbulence Level at Turbine Inlet

Tu

%

v

Subscripts h

Hub

m

Maximum value

t

Blade tip

x

Axial direction

0

Isolated airfoil

1

Inlet to plane 1

2

Outlet to plane 1

θ

Peripheral direction

vi

Chapter 1 : INTRODUCTION

1

Background Wells turbine was first proposed by Wells et al in 1976 (Raghunathan, 1985) to convert wave energy into mechanical energy. It is a self-rectifying air-driven axial turbine that harness the pneumatic power produced in the bidirectional airflow into unidirectional rotary motion. It is known for its mechanical simplicity, making it highly reliable compared to other air-driven turbines. Mauritius is conscious on the importance distributed energy generation from renewables. In 2010, the national grid was first made accessible by the Central electricity board (CEB) through the launching of the Small-Scale Distributed Generation (SSDG) project. This year 10,000 household and 10,000 small business will be fully subsidised by the government to install PV panels. This shows an encouraging effort of Mauritius to reduce its energy dependency on imported fossil fuels.

Sources of airflow for energy conversion using Wells turbine Wind energy Wind is a sustainable form of energy caused by the heating of the atmosphere by the sun, the rotation of the Earth, and the Earth’s surface irregularities. The use of wind energy through wind turbines to generate useful work date back to 5000 BC while electricity generation from wind turbine started in the 19th century. Wind energy is the most convenient source of energy for an airflow turbine at home. Since the turbine was designed for a household application, the source of energy used in this project was wind energy. The power available in wind, Pw can be expressed as,

𝑷𝒘 =

𝟏 𝝆𝑨𝒗𝟑 𝟐

Where, Ρ is the density of air and v is the velocity of the flowing air.

2

Wave energy Wave energy generation is suitable for producing power for small islands with high level of wave energy (Fadaeenejad et al., 2014). Positioned near the Tropic of Capricorn, Mauritius is highly influenced by the Southeast trade wind. The Mauritius Research Council (MRC) has signed a Collaborative Agreement with the Carnegie Wave Energy Ltd. to explore the potential of harnessing wave energy. A wave monitoring device was deployed in Souillac on June 2016. Professor Jugessur states to the press that the in the 1970’s, wave energy program started at the University of Mauritius; a study was undertaken with the assistance of a research grant from the Commonwealth Science Council on the wave energy potential in the South of Mauritius. The results were promising for pursuing the program further. However, due to the global changes in the price of energy and costly initial investments, it was hindered as it was economically more viable to buy mineral fuels and use the limited sugar-cane bagasse that were available. (Defi media, 2016). Moreover, Doorga et. 2018, reported the assessment of wave energy potential at three different regions on the Mauritian coastal environment. It was found that the eastern region was most promising for harnessing wave energy. Wave energy convertors are classified into; Oscillating Water Column (OWC), Overtopping devices and Oscillating bodies. OWC is a shoreline method for converting ocean wave energy. According to Raghunathan 1997, OWC devices are most practical for wave energy conversion. OWC was designed to extract the energy from oscillatory motion of ocean or sea waves. The system consists of an air chamber placed above the water level, allowing the moving waves to periodically change the water level causing an increase and decrease in air pressure. An airflow turbine connected above the air chamber rotates as the wave oscillates (Raghunathan et al., 1989). This project used the principle of OWC to generate rotational motion from wind energy using Wells turbine.

3

Turbines Turbines are devices which receives energy from the flowing fluid through a rotor and this energy is converted into mechanical energy. The turbine can be connected to a generator which converts the mechanical energy into electrical power. The turbines can be classified as steam, hydro, or air turbines based on the type of fluid. The power developed by the turbine is derived from equation (1). It is observed that power generated is a function of pressure head and volume flow rate across the turbine. 𝑷 = 𝜼𝝆𝒈𝑸𝑯

(1)

Based on energy transfer inside the turbine, there are two main types of turbines; impulse turbines and reaction turbines. In impulse turbines, the total pressure energy of the fluid is converted to kinetic energy before hitting the rotor blades, while in reaction turbines, both the pressure and kinetic energy changes as the fluid flow through the rotor blades. The torque of the turbine rotor T and the change in moment of momentum of the fluid across turbine rotor are related in the Euler turbo-machinery equation as shown below (Vavra, 1960),

𝑻 = ∫ 𝒓𝟏 𝑽𝟏 𝒅𝒎̇𝟏 − ∫ 𝒓𝟐 𝑽𝟐 𝒅𝒎̇𝟐 𝑺𝟏

(2)

𝑺𝟐

Where S1 and S2 is the surface of revolution at inlet and outlet respectively. By applying one-dimensional approximation, the equation becomes (Dixon, 1995), ̇ 𝒓𝟏 𝑽𝟏 − 𝒓𝟐 𝑽𝟐 ) 𝑻 = 𝒎(

4

(3)

Aim and Objectives The aim of this project is to investigate and design a Wells turbine for energy conversion for small scale power generation (50W) in a household. The objectives of the project are: ✓ Determining the optimum performance parameters of the Wells turbine through calculations. ✓ Design and drawing of the turbine and different components on a suitable 3D platform (Solidworks). ✓ Monitor the aerodynamic performance of the wind turbine with different blade number, using CFD.

✓ Building of a prototype of the Wells turbine. ✓ Comparing the experimental results to that obtained through modelling. The diagram below gives an overview of the process during the project using the approach used according to Raghunathan, 1995.

Figure 1: Illustration of the project objectives. The literature review (see section 2.14), it was found that there are a number of researches on the improvement of Wells turbine for maximum efficiency. However, there are not enough studies on the application of Wells turbine for residential applications. In this paper, a model of an optimized Wells turbine will be investigated and designed to convert airflow power for small domestic power generation. 5