Design, CFD Analysis and Modelling of Archimedean Spiral-type Wind Turbine-report

TRIBHUVAN UNIVERSITY INSTITUTE OF ENGINEERING THAPATHALI CAMPUS DESIGN, CFD ANALYSIS AND MODELLING OF ARCHIMEDEAN SPIRAL-TYPE WIND TURBINE BY ASIS BHATTARAI HARI BASHYAL SUDIP SAPKOTA UPAMA NEPAL A PROJECT SUBMITTED TO DEPARTMENT OF MECHANICAL AND AUTOMOBILE ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF ENGINEERING DEPARTMENT OF MECHANICAL AND AUTOMOBILE ENGINEERING THAPATHALI, NEPAL AUGUST, 2016

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The author has agreed that the library, Department of Mechanical and Automobile Engineering, Thapathali Campus, Institute of Engineering may make this report freely available for inspection. Moreover, the author has agreed that permission for extensive copying of this project report for scholarly purpose may be granted by the professor(s) who supervised the project work recorded herein or, in their absence, by the Head of the Department wherein the project report was done. It is understood that the recognition will be given to the author of this report and to the Department of Mechanical and Automobile Engineering, Thapathali Campus, Institute of Engineering in any use of the material of this project report. Copying or publication or the other use of this report for financial gain without approval of the Department of Mechanical and Automobile Engineering, Thapathali Campus, Institute of Engineering and author’s written permission is prohibited. Request for permission to copy or to make any other use of the material in this report in whole or in part should be addressed to: Head Department of Mechanical and Automobile Engineering Thapathali Campus, Institute of Engineering Thapathali, Kathmandu Nepal.

ABSTRACT

Wind energy is a relatively mature technology with enormous

potential for

commercialization and mass production. With highly efficient, solid and reliable wind turbine, wind power offers a solution to meet energy needs and environmental care. This is a report on one of the developing wind turbines known as Archimedean spiral-type wind turbine. This project report represents the preliminary design of Archimedean spiral-type wind turbine with the aid of calculations and the observations of various geometric parameters by CFD analysis along with its fabrication and testing. Through various simulations conducted at wind velocity of 3.5m/s , we selected a model of the turbine with the geometry as 150mm in diameter, 112.5 mm pitch and 60 degree of opening angle for maximum power coefficient. Results show that the wind turbine at the given parameters give the highest aerodynamic efficiency of around 0.25. CFD analysis was done for the selected model at a range of tip speed ratios and wind velocities. A range of 3.5m/s to 12m/s of the inlet wind velocity was taken and analyzed through CFD to calculate the power output of wind turbine. The maximum obtained power output was 4.7 W at wind speed of 12 m/s. Maximum power coefficient was obtained at tip-speed ratio of 1.5. Then, the best model was fabricated using a 3D printer and tested. The tests would be carried out in a wind tunnel of size 30cm*40cm and then compared with the theoretical results.

ACKNOWLEDGEMENT We would like to show our sincere gratitude to Department of Automobile and Mechanical Engineering for providing us the opportunity to conduct this thesis which we have anticipated will show us doors for further research and developments. We are thankful especially to Er. Laxman Palikhel, Head and Er. Kismat Maharjan, Deputy Head, for providing the prospect of conducting our final year project. We also would like to thank our colleagues for boosting us in conduction of this project. We owe our gratitude to our respected supervisor, Assistant Professor Mr. Ramendra Kumar for his untiring effort towards mentoring, guiding and supporting our project. We also express our deepest appreciation to Assistant Professor Mr. Sudip Bhattarai for providing the insights that led us to immense benefits.

Table of Contents COPYRIGHT.................................................................................................................................. APPROVAL..................................................................................................................................... ABSTRACT.................................................................................................................................... ACKNOWLEDGEMENT............................................................................................................... TABLE OF CONTENTS................................................................................................................. TABLE OF FIGURES..................................................................................................................... LIST OF TABLES........................................................................................................................... NOMENCLATURE....................................................................................................................... LIST OF ACRONYMS AND ABBREVIATIONS....................................................................... CHAPTER ONE: INTRODUCTION............................................................................................ 1.1 Backgroud............................................................................................................................ 1.2 Archimedes Spiral type Wind Turbine................................................................................. 1.3 Problem Statement............................................................................................................... 1.4

Objectives........................................................................................................................

1.4.1 General Objective......................................................................................................... 1.4.2 Specific Objectives....................................................................................................... 1.5

Methodology...................................................................................................................

1.5.1 Problem Statement........................................................................................................ 1.5.2

Literature Review....................................................................................................

1.5.3

Design......................................................................................................................

1.5.4

Fabrication...............................................................................................................

1.5.5

Testing and Results..................................................................................................

1.6 Scope of Work...................................................................................................................... 1.7 Limitations........................................................................................................................... CHAPTER TWO: LITERATURE REVIEW................................................................................ 2.1 Historical Background.........................................................................................................

2.2 Types of wind turbines......................................................................................................... 2.3 Features and components of HAWTS................................................................................. 2.4 Archimedean Spiral-Type Wind Turbine............................................................................. 2.4.1 The Archimedean Spiral............................................................................................... 2.4.2 Archimedes Rotor......................................................................................................... 2.5 Turbine Aerodynamics......................................................................................................... 2.5.1 Tip Speed Ratio............................................................................................................. 2.5.2. Power and Torque........................................................................................................ 2.5.3 Betz limit...................................................................................................................... 2.6 Finite Element Method (FEM):........................................................................................... 2.7 Computational Fluid Dynamics (CFD)............................................................................... 2.7.1 Principle theories relevant to CFD modelling.............................................................. 2.7.2 Turbulent models.......................................................................................................... 2.7.3 Solution Methods.......................................................................................................... CHAPTER THREE: RESEARCH METHODOLOGY................................................................ 3.1 Concept and Incubation....................................................................................................... 3.2 Software description............................................................................................................ 3.3 Design Parameters estimation:............................................................................................ 3.3.1 Wind Velocity............................................................................................................... 3.3.2 Angular Velocity (RPM)............................................................................................... 3.3.3 Pitch of the blade.......................................................................................................... 3.3.4. Opening angle.............................................................................................................. 3.4 Aerodynamic Analysis of the Turbine................................................................................. 3.4.1 Construction of Geometry............................................................................................ 3.4.2 Grid Generation (Mesh Geometry)............................................................................... 3.5 Fluent Simulation................................................................................................................. 3.6 Quality of Mesh................................................................................................................... 3.7

Fluent setup parameters..................................................................................................

3.8

Boundary conditions.......................................................................................................

3.9

Determination Of Best Model.........................................................................................

List of Figures Figure1.1 Phases of Design Process Figure

Nomenclature U

Free stream velocity

k

Turbulent kinetic energy



Specific dissipation rate

A

Swept area

Cp

Power coefficient

Cd

Drag Coefficient;

P

Power

d

Shaft diameter

D

Rotor diameter

Re

Reynolds number

λ

Tip speed ratio

L

Blade length

T

Torque

N

Angular velocity

n

Factor of Safety

Sut

Ultimate tensile stress

Sy

Yield stress

C10

Dynamic load rating

C0

Static load rating

ρ

Density of air

Cf

Skin friction coefficient

τ

Shear Stress

Ufric

Frictional velocity

Δs

First cell height

Y+

Non-dimensional wall distance;

t

Blade thickness

θ

Opening angle

u

Velocity in X-direction

v

Velocity in Y-direction

w

Velocity in Z-direction

p

Pressure

m/s

Meter per second

N-m

Newton meter

Pa

Pascal

MPa

Mega Pascal

kN

Kilo Newton

rad/s

Radian per second

W

Watt

kW

Kilo watt

MW

Mega watt

TWh

Tera watt hour

rpm

Revolutions per minute

LIST OF ACRONYMS AND ABBREVIATIONS HAWT

Horizontal Axis Wind Turbine

VAWT

Vertical Axis Wind Turbine

GHG

Green House Gases

CFD

Computational Fluid Dynamics

AEPC

Alternative Energy Promotion Centre

VDC

Village Development Committee

DHM

Department of Hydrology and Management

FEM

Finite Element Method

FVM

Finite Volume Method

FDM

Finite Difference Method

RANS

Reynolds Averaged Navier Stokes equation

LES

Large Eddy Simulation

DES

Detached Eddy Simulation

SST

Shear Stress Transport

SAE

Society of Automotive Engineers

CHAPTER ONE INTRODUCTION 1.1 Backgroud To secure the energy supply issues and address the climate change, reductions of Greenhouse Gas (GHG) emissions, biodiversity protection, development of renewable technologies, energy conservation, and efficiency improvements are becoming increasingly important. Among the renewable resources, wind energy is a fairly established technology with huge possibility for commercialization and bulk production. The major application of wind power is electricity generation from large grid-connected wind farms [1]. With the expansion of the power grid and the reduction of electricity scarce areas, small-scale wind turbines are now being applied in several countries and in many fields, such as city road lighting, mobile communication base stations, offshore aquaculture, and sea water desalination [2]. Small scale wind turbines yet have not been addressed and taken seriously in context of Nepal. Though with many potentials and with growing energy problems, this small but significant technology can provide much assistance in the households of Nepalese community. 1.2 Archimedes Spiral type Wind Turbine Archimedean Spiral-Type Wind Turbine is small scale horizontal axis wind turbine designed on Archimedean spiral principles. It harvests energy from the wind by redirecting its flow 90 degrees relative to the original direction. Unlike traditional HWATs, which use lift force to take power from wind energy, the ASWT uses both the lift and drag force. It can utilize kinetic energy from wind energy. In particular, the advantage lies in the ASWT operating at low wind speeds. 1.3 Problem Statement 1. Low efficiency of small scale wind turbine available. 2. High level noise for Horizontal axis wind turbines which is why the turbines cannot be fit in the nearby surrounding.

3. High cut-in speed of small scale wind turbine which is quite a problem, so it cannot be installed anywhere. 4. High tip speed ratio is required for obtaining maximum power coefficient which determines a wind turbine’s capacity. 1.4 Objective 1.4.1 General Objective To design, conduct CFD analysis and develop a model of Archimedes spiral-type wind turbine. 1.4.2 Specific Objectives 1. 2. 3. 4.

Selection of best model of Archimedes wind turbine with the help of CFD analysis. Numerical study to calculate the mechanical output. Fabricate a scaled down model to fit in the wind tunnel available. Experimental verification through wind tunnel test for the fabricated model.

1.5 Methodology The methodology adopted during the project is described below: 1.5.1 Problem Statement The problems that the project had to infer or deal with were assessed through various discussions with experts who have been working on the required field. As a result, we found that an appropriate small scale wind turbine that could fulfill the energy requirements defected due to loadshedding problems could be a real boon for the energy crisis of the country. 1.5.2 Literature Review The literature review was carried out throughout the schedule until the project’s completion. It was done through web-based research, expert consultations and manual study. The literature related to simulation and optimization was studied on the internet. Research on selection for design parameters for the turbine was carried out thoroughly. The turbines that were studied previously and installed were looked into in order create a basis for the turbine used in the project. 1.5.3 Design The selection of the most efficient design for the given constraints was done by following steps given below:

1.5.4 Fabrication The fabrication was done using 3d- printer for the construction of the turbine blade and shaft produced integrated as a whole. Then, the frame was attached separately using suitable materials unified with the other part using appropriate processes, resources and tools. 1.5.5 Testing and Results The turbine was tested for the comparison of the theoretical values obtained during CFD analysis with the experimental values. The testing was exercised in the wind tunnel available in the laboratory of Kathmandu University (KU). 1.6 Scope of Work The Archimedes wind turbine targets the households of urban areas as the wind energy available could be harvested. The proposed turbine could be installed at a place where the wind speed is less than 3 m/s. The turbine easily fits on the roof just as the solar panels. So, the turbine can be used in cities in order to fulfill the daily energy needs. The turbine can also be used for following applications such as in between the large power generating wind turbines which require minimum speed of more than 3m/s, street lighting, as hybrid source

with solar panels for constant output as well as used as backup sources for different purposes. 1.7 Limitations 1. Unavailability of appropriate wind tunnel for testing procedure. 2. CHAPTER TWO: LITERATURE REVIEW 2.1 Historical Background Wind energy has been used for thousands of years for milling grain, pumping water and other mechanical power applications. Wind energy was the fastest growing energy technology in the 1990s, in terms of percentage of yearly growth of installed capacity per technology source. By the end of 1999, around 69% of the worldwide wind energy capacity was installed in Europe, a further 19% in North America and 10% in Asia and the Pacific. . Greenpeace states that about 10% of electricity can be supplied by the wind by the year 2020. Considering Nepal, it is a mountainous country with a high potential for wind energy. On average, Nepal gets 18 hours of wind every day in particular areas and at least two days a week, it is really windy all over the country. The analysis done by the Solar and Wind Energy Resource Assessment concludes that about 6, 074 square kilometers of land all over the country has the potential for wind power with density greater than 300 watt per square meter. The analysis established that more than 3,000MW of power with an installed capacity of 5MW per sq km was possible and Kathmandu Valley alone was capable of producing 70MW, whereas two districts, Mustang and Manang, have a potential of more than 2500MW. Wind generation capacity is particularly high in the river corridors and mountain valleys. Wind power development in Nepal dates back to 1970s with a pilot project in Agricultural farm of Rampur VDC of Chitwan district and installation of wind turbine for pumping water in Ramechhap district. The first wind turbine of 20 kW capacity was installed in Kagbeni of Mustang District in 1989, however blade and tower of the wind generator were broken within a short period of installation and it is not in operation anymore. Wind turbines were installed in Chisapani of Shivapuri National Park and the Club Himalaya in Nagarkot, both of which are not functional anymore. In 2011, Alternative Energy Promotion Centre with the financial support from Asian Development Bank installed two 5 kW wind turbines in Dhaubadi village of Nawalparasi District with solar hybrid systems for rural electrification.

There were also other attempts made by Research Centre for Applied Science and Technology, Nepal Army, Practical Action, AEPC, Department of Hydrology and Meteorology (DHM) among others. These organizations have collected vital information regarding prospects of wind energy in Nepal while installing wind turbines in their selected sites. A modern large wind turbine is not practical in Nepal as the blades cannot be disassembled and need to be delicately handled, which requires good road access for transportation. So for the time being, smaller wind turbines are ideal for the country. The hill effect on wind turbines placed on hills provides additional benefits to the wind turbine projects in Nepal. Surrounding mountainous range around the Kathmandu Valley is about 105 km and if small wind turbines as pilot project could be installed at an interval of 100 meters, it could generate about 5MW. If they are installed as a cluster, certainly more power could be obtained. . The development of small scale wind power system could be done including turbine, generator, controller and tower using local resources. Lack of proper testing to obtain performance of the system such as power curve with respect to tip speed ratio and unavailability of wind data are the major factors impeding the development of the technology. . With a good design, the system can be manufactured locally to reduce the cost of the technology. The indigenous manufacturing techniques can be used with some clever design of wind turbine rotor and low speed permanent magnet generator. 2.2 Types of wind turbines There are two great classes of wind turbines: those whose rotors spin about a horizontal axis and those whose rotors spin about a vertical axis. Vertical-axis wind turbines (VAWT) can be divided into two major groups: those that use aerodynamic drag to extract power from the wind and those that use lift. The vertical axis of rotation also permits mounting the generator and drive train at ground level. The disadvantages of this type of rotors is that it is quite difficult to control power output by pitching the rotor blades, they are not self – starting and they have low tip-speed ratio. Horizontal – axis wind turbines (HAWT) are convectional wind turbines and unlikely the VAWT are not omnidirectional. In a HAWT the generator converts directly the wind which is extracted from the rotor. The rotor speed as well as the power output can be controlled by pitching the rotor blades along their longitudinal axis. A mechanical or an electronic blade pitch control mechanism can be used in order to achieve this. An important advantage for HAWT is that blade pitching acts as a form of protection against extreme wind conditions

and over speed. Also the rotor blades can be shaped to achieve maximum turbine efficiency, by exploiting the aerodynamic lift to the maximum. 2.3 Features and components of HAWTS The main parts of a HAWT are the blades, the hub, the transmission system, the gearbox, the generator and the yaw and pitch control systems. The blades are the key to the operation of the wind turbine. Three – bladed designs are the most common for modern wind turbines. The blades of a HAWT are fastened to the central hub. As the rotor turns, its blades generate an imaginary surface whose projection on a vertical plane is called the swept area. 2.4 Archimedean Spiral-Type Wind Turbine The Archimedes spiral wind turbine, which is a new HAWT concept, was designed using the Archimedes spiral principles. Unlike traditional HAWTs, which use the lift force to take power from wind energy, the Archimedes spiral wind turbine uses both the lift and drag force. The Archimedes spiral wind turbine can utilize the kinetic energy from wind energy. This special structure determines the special aerodynamic characteristics of small scale wind turbines. In particular, the advantages of the Archimedes spiral structure will be more obvious in many circumstances, such as around buildings, because the wind turbine operates at low wind speeds. The wind direction in an urban environment changes constantly but the Archimedes wind turbine follows the wind direction automatically because the yaw is passively controlled due to the drag force. Other advantages include low noise because of the relatively low rotational speed. The disadvantage of the Archimedes wind turbine is the high thrust force compared to a propeller-type conventional HAWT. 2.4.1 The Archimedean Spiral Archimedean spiral is a spiral named after the 3rd century BC Greek Mathematician Archimedes. It is the locus of points corresponding to the locations over time of a point moving away from a fixed point with a constant speed along a line which rotates with constant angular velocity. In polar coordinates (r, θ) it can be described by the equation r=a+bθ

2.4.2 Archimedes Rotor The Archimedes rotor has the characteristics of both resistance and lift type turbine. A resistance characteristics are that the turbine blades are flat sheets, can work under a large margin of error, produce very low noise and is lightweight. Likewise, the turbine rotor can work with tip speed ratio greater than 1, and its efficiency is extremely high which are the characteristics of the lift type. The rotor is designed on the basis of Archimedean Spiral. The spiral shape given to the blade enables the air to flow thoroughly within the blade and use both drag and lift force. The rotor consists of three blades connected with each other with 120 deg. And each blade has a symmetric arrangement around the shaft and its shape is similar to a triangular pyramid. The spiral wind blade with an Archimedes shape shows relatively high rotor efficiency compared to the aerodynamic performance of the other blades like the Savonius type rotor in the lower tip speed ratio range.

Archimedes spiral wind turbine, is one of the HAWT, however, there is marked contrast between new wind turbine design and traditional HAWT models. The spiral allowed better measurement of a circle’s circumference and thus its area. However, this spiral was soon proved inadequate when Archimedes went on to determine a more accurate value of Pi that created an easier way of measuring the area of a circle. In old HAWT scheme, lift force is the one of the main factor to take power from wind energy, but the Archimedes spiral small wind turbine is mainly depended on the drag force. In Fig. diagram of Archimedes spiral wind turbine is illustrated which can produce around 100W.

Fig 1.Geometry of Archimedes Wind Turbine Blade In March 2007, Tu Delft carried out a test which showed the efficiency of approximately 10%. In 2009 an improved model was tested at the Peutz wind research center which broke at 21 m/s so the number of revolutions along the rotor axis was reduced to one. This increased efficiency to about 15 %. In 2012 a very detailed study at Pusan Korea University was begun. CFD analysis confirmed the calculations made earlier and the theoretical efficiency was determined at 25%. Over the two subsequent years rotor efficiency rose to an astonishing 52 %. 2.5 Turbine Aerodynamics 2.5.1 Tip Speed Ratio

The tip speed ratio is the ratio of the blade tip speed over wind speed. It is a significant parameter for wind turbine design and its definition is shown in the equation below: Definition of tip speed ratio  ¿

ω∗R V0

� is the angular velocity of the wind turbine rotor, R is radius of the rotor and

V 0 is the

wind speed. A higher tip speed ratio generally indicates a higher efficiency. The relationship between rotational speed and tip speed ratio is shown in below equation: =

2 Πnr 60V 0

Where n is the rotational speed of the rotor, r is the rotor radius and V0 is the wind speed. Thus, an inverse relationship between the rotational speed and the blade span can give the required speed. Due to the same tip speed ratio, a blade with a big span has a low rotational speed. 2.5.2. Power and Torque In reality, a wind turbine cannot derive all the wind power from wind stream when it passes through the rotor of the wind turbine, which means that some part of the kinetic energy of the wind is transferred to the rotor and the rest of the energy leaves the rotor. Therefore, the amount of wind energy which is converted to the mechanical power by the rotor is defined as the efficiency that is usually termed as the power coefficient, Cp. τ∗ω Aerodynamic Efficiency, Cp=

1 ∗ρ∗A∗V 3 2

Where, �= torque �= Angular velocity A= Cross-sectional Area of the Blade V= wind Velocity

2.5.3 Betz limit

The efficiency is defined as the ratio between power coefficient Cp and the Betz limit, Betz = 16/27 ≈ 0.593. This value was concluded by Albert Betz who was a German physicist in 1919, 0.593 is the maximum power efficiency of a wind turbine which converts the kinetic energy to mechanical energy, So efficiency is given by: Betz limit=

16 C 27 p

Where Cp= power coefficient 2.6 Finite Element Method (FEM): The FEM is one of the most significant numerical methods for solving the partial differential equations which are faced in engineering problems. This process uses a variational problem which involves an integral of the differential equation over the model domain. This domain is divided into a finite number of sub domains called elements and the elements are connected to each other at the points called nodes. The sub domains can be solved by defining approximate interpolation or shape functions for each element.

These functions

should be a complete set of polynomials, which maybe linear, quadratic or higher order. When the polynomial functions of all the elements are known then they are placed together in order to find a solution for the entire region. The major steps in FEM are: 1. Find the strong form of the governing differential equation of the system. 2. Convert the strong form of the equation to the weak form. 3. Choose suitable interpolation (shape) functions. 4. Choose the weight functions and set up the algebraic equations for each element. 5. Obtain the global matrix system of the equations through the assembly of all elements. 6. Impose boundary conditions. 7. Solve the system of algebraic equations. 8. Post process the results. 2.7 Computational Fluid Dynamics (CFD) CFD is a numerical method which can be used to predict fluid flow, heat transfer and chemical reactions in complex systems. CFD has been applied most widely in the industrial and non-industrial application areas due to less times and cost requirement in designing the models. In order to analyze a fluid problem with CFD, we need to obtain the mathematical equations which describe the behavior of the fluid flow. 2.7.1 Principle theories relevant to CFD modelling No matter what kind of CFD software is, the main processes of simulation are the same. Setting up governing equations is the precondition of CFD modelling; mass, momentum and

energy conservation equation are the three basis governing equations. After that, Boundary conditions are decided as different flow conditions and a mesh is created. The purpose of meshing model is discretized equations and boundary conditions into a single grid. A cell is the basic element in structured and unstructured grid. The basic elements of two-dimensional unstructured grid are triangular and quadrilateral cell. Meanwhile, the rectangular cell is commonly used in structured grid. In three-dimensional simulation, tetrahedral and pentahedral cells are commonly used unstructured grid and hexahedra cell is used in structured grids. The mesh quality is a prerequisite for obtaining the reasonably physical solutions and it is a function of the skill of the simulation engineer. The more nodes resident in the mesh, the greater the computational time to solve the aerodynamic problem concerned, therefore creating an efficient mesh is indispensable. Three numerical methods can be used to discretize equations which are Finite Difference Method (FDM), Finite Element Method (FEM) and Finite Volume Method (FVM). FVM is widely used in CFD software such as Fluent, CFX, PHOENICS and STAR-CD, to name just a few. Compared with FDM, the advantages of the FVM and FEM are that they are easily formulated to allow for unstructured meshes and have a great flexibility so that can apply to a variety of geometries. 2.7.2 Turbulent models In CFD software, wind turbines are simulated under the turbulent flows. There are three different types of simulated methods under the Indirect Numerical Simulation which are large eddy simulation (LES), Reynolds-averaged Navier-Stokes (RANS) and detached eddy simulation (DES). The equation of Reynolds-averaged Navier-Stokes (RANS) is defined as:

[(

D Ui ∂ P ∂ Ui ∂ Ui ∂ = + μ + − ρu' j u' i Dt ∂ X i ∂ X i ∂ x j ∂ xi

)

]

The left hand side of the equation describe the change in mean momentum of fluid element and the right hand side of the equation is the assumption of mean body force and divergence stress.

ρ u' j u'i

is an unknown term and called Reynolds stresses.

2.7.3 Solution Methods o Standard k−ε model: it has a nice stability and precision for high Reynolds number turbulent flow but it is not suitable for some simulation with rotational effect.

o RNG k−ε model: it can used for low Reynolds number flow, as considering the rotational effect, the simulated accuracy will be enhanced in rapidly strain flow. o Realizable k−ε model: it is more accurate for predicting the speeding rate of both planar and round jets but it will produces non-physical turbulent viscosities when the simulated model includes both rotating and stationary fluid zone o Standard k-ω model: it contains the low-Reynolds-number effects, compressibility and shear flow spreading. It has a good agreement with measurements with problems of far wake, mixing layers and plane, round, and radial jets. o Shear-stress transport (SST) k-ω model: because it absorbs both the property of good accuracy in the near-wall region of standard k-ω model and nice precision in the far field region of k−ε model, it is more accurate and reliable for a wider class flow than the standard k-ω model. o Reynolds stress model: Abandoning the eddy-viscosity hypothesis, the Reynolds stress model (RSM) calculates the Reynolds stresses directly. Theatrically, it is much more accurate than k−ε and k-ω model, but five additional transport equations

in 2D flows and seven additional

transport equations in 3D flows seize huge resources in computer and a long simulated time. CHAPTER THREE RESEARCH METHODOLOGY 3.1 Concept and Incubation The research is conducted on Initially, different designs of turbine along with blades and shaft are put into simulation software and a virtual condition is created. Then, their aerodynamic properties are checked in order to find the best model. Initially, only a single wind speed is taken and 3.2 Software description To obtain the desired geometry of the turbine, SOLIDWORKS 15 is used to design the turbine’s geometry. SOLIDWORKS provide correct guidance and easiness while designing the turbine. Likewise, the CFD simulation process was conducted with academic multipurpose CFD solver, ANSYS FLUENT. The code is idealized according to the Reynolds Averaged Navier

Stokes Equation and the Finite Volume Method of the governing equations. The k-ω Shear Stress Transport (SST) turbulence model is used to predict the separation of flow accurately. The mesh was generated used the ANSYS MESHING. 3.3. Design Parameters estimation In order to define the system used in the turbine simulation, various parameters are used that give the turbine its virtual existence. There are basically two kinds of parameters used. The first ones are the Input parameters and the second ones are the Variable parameters. Some geometric constraints are also taken into account. The Input parameters are: 1. Wind Velocity 2. Angular Velocity (RPM) The variable parameters are: Pitch 1. Opening Angle Geometric constraints: 1. Blade Diameter 3.3.1 Wind Velocity The velocity of the input wind is the known as the wind velocity. In context of Nepal, various ranges of wind speeds are found. But, the average wind velocity of Kathmandu Valley is 3.5 m/s which is taken into account and considered as the constant wind velocity throughout various simulations of the turbine geometries and when the best geometry is obtained, the wind velocity is relatively varied. 3.3.2 Angular Velocity (RPM) Angular velocity is the velocity at which the turbine rotates. Exactly a single rotational velocity cannot be taken into consideration on random basis since its not sure what velocity gives the maximum efficiency of the turbine so a range of the rotational velocities are input and analyzed. 3.3.3 Pitch of the blade The pitch of the wind turbine blade is an essential parameter for designing the turbine. It controls the rotational speed of the turbine and limits it as the speed of the wind changes. The estimation of the proper pitch becomes a detrimental factor for producing maximum power and minimizing the fatigue loads on the turbine. The pitch is varied and studied in the simulation process.

3.3.4. Opening angle The opening angle of the turbine determines what amount of air circulates within the blades’ faces and periphery. It also determines the tip vortex created at the end of the turbine blade. Likewise, the pressure difference created along the blades of the turbine also gets affected with the change in opening angle. The opening angle is varied and studied in the simulation process. 3.4 Aerodynamic Analysis of the Turbine 3.4.1 Construction of Geometry The turbine incorporates a single shaft and three blades of equal diameter. The turbine is initially designed in SOLIDWORKS 15. The blades are kept at a diameter of 150 mm. Likewise, a helix of variable pitch provided in the software is used to give the curvature that the blade required and the required variable pitch is input accordingly. Total of 20 different geometries of various dimensions of same parameters were constructed.

Figure: Model of turbine rotor with pitch at 112.5 mm 3.4.2 Grid Generation (Mesh Geometry)

The geometry is now imported in ANSYS MESHING 16. A single domain is created where the turbine is incorporated. Around the turbine geometry, an O-grid is created. The O-grid facilitated us with the advantages of dense mesh around the turbine and proper inflation. The nodes provided differed according to the mesh density required. Wall distance for the first edge near the wall is calculated using reference length, flow velocity and other flow parameters like density and viscosity. +¿=

u∗y v

Y¿ Where u is the friction velocity at the nearest wall, y is the distance to the nearest wall; ν is the local Kinematic Viscosity of the fluid. Y+ is the non-dimensional wall distance for a wall bounded flow. The Y-plus value of the model is found to be in the range from 0.2mm to 0.32 mm according to the increase in velocity which was taken from the online source www.cfdonlinetools.com using the Y-Plus Distance Estimation tool. The input parameter being free-stream velocity, density of fluid, dynamic viscosity, boundary layer length and desired Y-Plus value to be 1mm, we get the approximate value of Reynolds number and the y-plus value. The input parameters for the Y-plus estimation is given below: Table 4.1: Basic Parameters S.N. 1. 2. 3. 4.

Parameters Freestream Velocity Density Dynamic Viscosity Boundary Layer length

Value 3.5 m/s 1.225 kg/m3 1.875*10-5 kg/ms 0.162 m

3.5 Fluent Simulation The developed mesh is imported to Fluent and the setup is done. During setup, the fluid properties and the turbulence model are chosen, and the flow velocity and pressure values are supplied using boundary conditions. The cell conditions are changed to fluid in the ANSYS MESHING itself. The setup is then initialized and then calculation is done. 3.6 Quality of Mesh The statistics relating to mesh is given below: Table 6.2: Mesh Statistics Mesh metric

Minimum value

Maximum

Average Value

Standard

Orthogonal

5.7401*10-3

value 0.99999

0.69143

Deviation 0.29708

Quality Aspect

1.1605

135.54

4.3035

5.3091

Ratio Jacobian Ratio Warping Factor Parallel

-100 0 0

212.94 0.23646 101.68

1.0692 1.6622*10-2 10.688

0.61786 1.8075*10-2 11.145

Deviation 3.7 Fluent setup parameters For the relevant comparison of different geometry, fluent setup parameters are kept same for each trail. The models selected are as follows: Viscous model: SST -with all parameters kept by default Material: Simple air (Incompressible) Viscosity: Constant Ambient pressure and temperature: Standard atmosphere (101325 Pa and 300K) 3.8 Boundary conditions The constant speed of the turbine is 3.5 meters per second. The operating condition is at sea level. The fluid is thus at normal atmospheric pressure. Therefore, the gauge pressure is taken as 0. The Reynolds number was calculated as Re = 4.937* 10 4 using the following equation: ℜ=

ρVl μ

Where, ρ=1.225 kg/m3, µ= 1.875 *10-5 kg/m-s, D= chord length= 162mm Different models were used for the same boundary conditions but with varying tip-speed ratios.

Table 4.3: Table representing Different Boundary Conditions S.N.

Zone

Boundary Type

Operating Condition

1.

Inlet

Velocity Inlet

3.5 m/s

2.

Interior-domain

Interior

0

Pressure Outlet

Pressure) 0 Pascal(Gauge

3.

Outlet

pascal

(Gauge

pressure) 4.

Top, Bottom

Velocity Inlet

3.5 m/s

Velocity inlet boundary condition is defined to provide the flow velocity of the incompressible fluid flow. The velocity magnitude and direction helps to provide the flow at

different

inclination

from

the

global

axes.

Pressure outlet boundary conditions require the specification of a static (gauge) pressure at the outlet boundary. Reference Values The reference values to be set are Area, Density, Enthalpy, Length, Pressure, Temperature, Velocity, Dynamic Viscosity and Ratio of Specific Heats. For the analysis, all the parameters are set to default once we choose to compute from Inlet. Solver Second order discretization upwind is used to solve the problem with a pressure based solver. Each boundary conditions are initialized with flow velocity value. Then iterations are run. Two pressure-based solver algorithms are available in ANSYS FLUENT, a segregated algorithm, and a coupled algorithm. A coupled algorithm or scheme is selected for the problem.

3.9 Determination Of Best Model The results of simulations of various geometries where each geometry is analyzed through a range of tip speed ratios from 1 to 2.25 due to which is considered to obtain the maximum output are given below Table 7.1: Simulation data for different tip speed ratios at P=0.25R Λ 1 1.25 1.5 1.75 2

ω(rad/s) 46.666666

T(N-m) 0.001039

P(W) 0.048507

Cp 0.1045262

67 58.333333

444 0.000864

396 0.050429

58 0.1086675

33

501 0.000725

234 0.050780

35 0.1094253

81.666666

442 0.000610

905 0.049846

33 0.1074114

67 93.333333

363 0.000471

303 0.044004

04 0.0948235

70

33

479

691

95

Here, for pitch= 18.75mm, for tip speed ratio of 1.5 which yields 70 rad/s of angular velocity, the maximum power coefficient Cp obtained is 0.109425333.

Cp vs λ

Figure 3.3: Graph representing Cp Vs λ at P=0.25R

Table 7.2.: Simulation data for different tip speed ratios at P=0.5R Λ

ω(rad/s) 58.333333

T(N-m) 0.001093

P(W) 0.063782

Cp 0.1374419

1.25

33

415 0.000952

565 0.066659

86 0.1436408

1.5

70 81.666666

276 0.000823

289 0.067253

99 0.1449215

1.75

67 93.333333

514 0.000704

612 0.065752

79 0.1416869

2

33

491 0.000584

514 0.061328

34 0.1321545

2.25

105

084

813

13

Here, for pitch= 37.5mm, for tip speed ratio of 1.75 which yields 81.66 rad/s of angular velocity, the maximum power coefficient Cp obtained is 0.144921579.

Cp vs λ

Figure 3.3: Graph representing Cp Vs λ at P=0.25R Table 7.3: Simulation data for different tip speed ratios at P=0.75R λ

ω(rad/s) 58.333333

T(N-m) 0.001577

P(W) 0.092020

Cp 0.1982896

1.25

33

487 0.001407

093 0.098536

78 0.2123316

1.5

70 81.666666

665 0.001218

522 0.099501

19 0.2144108

1.75

67 93.333333

385 0.001031

434 0.096279

6 0.2074674

2

33

563 0.000818

213 0.085971

53 0.1852549

2.25

105

772

086

65

Here, for pitch= 56.25 mm, for tip speed ratio of 1.75 which yields 81.666 rad/s of angular velocity, the maximum power coefficient Cp obtained is 0.21441086.

Cp vs λ

λ

ω(rad/s) 58.333333

T(N-m) 0.001325

P(W) 0.077333

Cp

1.25

33

717 0.001174

509 0.082213

0.166642265

1.5

70 81.666666

482 0.001068

768 0.087251

0.1771585

1.75

67 93.333333

381 0.000925

115 0.086408

0.188013237

2

33

805 0.000752

441 0.078988

0.186197401

2.25

105

271

437

0.17020839

Figure 3.4 : Graph representing Cp Vs λ at P=0.75R

Table 7.4: Simulation data for different tip speed ratios at P=R Here, for pitch= 75mm, for tip speed ratio of 1.75 which yields 81.666 rad/s of angular velocity, the maximum power coefficient Cp obtained is 0.188013237.

Cp Vs λ

Figure 3.5 : Graph representing Cp Vs λ at P=R

Table 5.4: Simulation data for different tip speed ratios at P=1.25R

λ

ω(rad/s) 46.666666

T(N-m) 0.001985

P(W) 0.092672

Cp 0.1996964

1 1.25

67 58.333333

849 0.001745

935 0.101835

56 0.2194393

33

743 0.001515

02 0.106075

94 0.2285771

1.5

70 81.666666

365 0.001294

55 0.105730

08 0.2278336

1.75

67 93.333333

66 0.001045

55 0.097611

85 0.2103380

2

33

836 0.000785

379 0.082505

72 0.1777863

2.25

105

763

133

48

Cp vs λ

Figure 3.6 : Graph representing Cp Vs λ at P=1.25R

Table 5.6: Simulation data for different tip speed ratios at P=1.5R λ

ω(rad/s) 46.666666

T(N-m) 0.002121

P(W) 0.098984

Cp 0.2132971

1

67 58.333333

098 0.001834

587 0.106990

33 0.2305487

1.25 1.5

33 70

123 0.001565

532 0.109579

58 0.2361286

81.666666

428 0.001275

981 0.104192

38 0.2245193

1.75

67 93.333333

826 0.000980

473 0.091559

56 0.1972975

2

33

996

657

06

Cp vs λ

Figure 3.7 : Graph representing Cp Vs λ at P=1.5R

Table 5.7: Simulation data for different tip speed ratios at P=1.75R λ 0.75 1

ω(rad/s)

T(N-m) 0.002591

P(W) 0.090703

Cp 0.1954519

207 0.103189

85

46.666666

52 0.002211

67

203

455

0.222358

35

1.25 1.5 1.75

58.333333

0.001875

0.109379

0.2356967

33

078 0.001541

538 0.107924

14 0.2325615

81.666666

78 0.001206

593 0.098538

22 0.2123351

67

59

175

81

70

Cp vs λ

Figure 3.8 : Graph representing Cp Vs λ at P=1.75R

Table 5.8: Simulation data for different tip speed ratios at P=2R λ 0.75

ω(rad/s) 35

T(N-m) 0.002677

P(W) 0.093722

Cp 0.2019581

46.666666

787 0.002238

528 0.104473

73 0.2251253

1

67 58.333333

722 0.001848

689 0.107849

34 0.2324007

1.25

33

857 0.001458

963 0.102114

04 0.2200416

1.5

70 81.666666

778 0.001080

488 0.088215

06 0.1900913

1.75

67 93.333333

19 0.000689

492 0.064335

27 0.1386341

2

33

312

822

73

Cp vs λ

Figure 3.9: Graph representing Cp Vs λ at P=2R

After analyzing the above data and graphs, we conclude a final pitch value where the maximum power coefficient is obtained which is at P=1.5R with tip speed ratio of 1.5. Opening Angle: Now, some of the opening angles which are previously used in other HAWTS are used and varied to find out the optimum result.

Table 5.9: Simulation data for different tip speed ratios at Angle=30 degrees λ

ω(rad/s)

T(N-m) 0.00225038

P(W)

Cp 0.16972353

0.75

35 46.6666666

4 0.00170199

0.07876343

1 0.17115178

1

7 58.3333333

1 0.00117384

0.079426237

4 0.14755197

1.25

3

5 0.00065293

0.068474298

5 0.09848881

1.5

70

7

0.045705604

1

Cp vs λ

Figure 3.10: Graph representing Cp Vs λ at opening angle at 30 degrees

Table 5.10: Simulation data for different tip speed ratios at Angle=45 degrees λ

ω(rad/s) 46.6666666

T(N-m) 0.00215449

P(W)

Cp 0.21665506

1

7 58.3333333

1 0.00175170

0.100542899

5

1.25

3

8 0.00135961

0.102182973

0.22018918 0.20508372

1.5

70 81.6666666

4 0.00096811

0.095173001

9 0.17036853

1.75

7

5

0.079062758

9

Cp vs λ

Figure 3.11 : Graph representing Cp Vs λ at opening angle at 45 degrees

Table 5.11: Simulation data for different tip speed ratios at Angle=60 degrees λ

ω(rad/s) 46.6666666

T(N-m) 0.00212109

P(W)

Cp 0.21329713

1

7 58.3333333

8 0.00183412

0.098984587

3 0.23054875

1.25

3

3 0.00156542

0.106990532

8 0.23612863

1.5

70 81.6666666

8 0.00127582

0.109579981

8 0.22451935

1.75

7 93.3333333

6 0.00098099

0.104192473

6 0.19729750

2

3

6

0.091559657

6

Cp vs λ

Figure 3.12 : Graph representing Cp Vs λ at opening angle at 60 degrees

Table 5.12: Simulation data for different tip speed ratios at Angle=75 degrees λ

ω(rad/s) 58.3333333

T(N-m) 0.00164705

P(W)

Cp 0.20703412

1.25

3

4 0.00144414

0.096078121

8

1.5

70 81.6666666

6 0.00124899

0.101090206

0.21783443 0.21979731

1.75

7 93.3333333

3 0.00104690

0.10200112

4 0.21055286

2

3

4

0.097711059

7

Cp vs λ

Figure 3.13 : Graph representing Cp Vs λ at opening angle at 75 degrees

Table 5.13: Simulation data for different tip speed ratios at Angle=90 degrees λ

ω(rad/s) 58.3333333

T(N-m) 0.00123573

P(W)

Cp 0.15533181

1.25

3

7 0.00108256

0.072084682

8 0.16329401

1.5

70 81.6666666

7 0.00093000

0.07577969

4 0.16366238

1.75

7 93.3333333

8 0.00077178

0.07595064

7 0.15522085

2

3

4

0.072033188

8

Cp vs λ

Figure 3.14 : Graph representing Cp Vs λ at opening angle at 90 degree The final optimum results are given in the table below: Table 5.14: Pitch Vs Cp

PITCH(x R)

Cp

0.25

0.109425333

0.5

0.144921579

0.75

0.188013237

1

0.21441086

1.25

0.236128638

1.75

0.235696714

2

0..232400704

Where R=radius of the Turbine Blade= 75 mm

Table 5.15: Opening Angle Vs Cp Opening Angle, θ (degree)

Cp

30

0.171151784

45

0.22018918

60

0.236128638

75

0.219797314

90

0.163662387

Opening Angle vs Cp

Pitch vs Cp

So, from the data and graphs above, the best model selected would be the turbine with pitch at 112.5mm and the opening angle at 60 degrees.

Figure: At Constant Opening Angle (θ) of 60 degree, assembled pressure contours at a) P=0.5R b) P=0.25R c) P=0.75R d) P=R

a)

c)

b)

d)

Figure: At Constant Opening Angle (θ) of 60 degree, assembled pressure contours at a) P=1.25R b) P=1.5R c) P=1.75R d) P=2R

Figure: At constant pitch of 1.5R, pressure contours of turbines at a) Θ= 30 degrees b) θ=45 degrees c) θ= 60 degrees d) θ=75 degrees

a) c)

b) d)

The above figures show the calculated ensemble pressure contours of the overall flow field on the central plane of the Archimedes spiral wind turbine at three single wind speed of 3.5m/s, which were characterized by the contours. The tip speed ratios taken at in-flow velocity of 3.5 m/s were, respectively. The tip speed ratios were 1, 1.25, 1.5, 1.75, 2 and 2.25 respectively.

The flow field along the turbine rotor is from right to left. Because of the spiral effect, the velocities from the leading edge increases at the inner side of each blade. A recirculation zone with lower speeds is also observed in the wake regions because the incoming airflow is obstructed by the hub cone and rotor. A circular accelerating zone exists behind the rotor, which results in a low pressure near the wall of the rotating domain. A low-speed region formed behind the hub of the rotor, indicating the wake region. The pressure distribution is in the center plane of the wind turbine. When the blade is rotating, there is a pressure difference between the pressure side and the suction side. Due to the spiral surface of the blades, the pressure difference (a force) generates torque. In general, the front side of the blade has higher pressure while the corresponding rear side has a lower pressure. When the in-flow velocity increases, the pressure difference becomes larger. The pressure difference is large at the blade tip but small at the root region. This means that most of energy can be extracted near the blade tip like a three blade HAWT. The maximum pressure differences between the root and tip were approximately 3 Pa. On the suction side, however, the pressure differences are much higher. The pressure differences were more than 15 Pa lower at the tip than the root. Therefore, the pressure difference between the two sides at a section increase towards the tips of each blade. For all the cases, the rear side pressure is negative, so that thrust force can be exerted to the shaft. Aerodynamic characteristics of Best Geometry Model: At 3.5 m/s, λ 0 0.25 0.5 0.75 1 1.25 1.5 1.75

ω(rad/s) 0 11.66666667 23.33333333 35 46.66666667 58.33333333 70 81.66666667

T(N-m) 0.002676918 0.002515319 0.00284726 0.002549867 0.002121098 0.001834123 0.001565428 0.001275826

P(W) 0.029345388 0.066436069 0.089245349 0.098984587 0.106990532 0.109579981 0.104192473

ω 0 20 40 60 80

T 0.008046714 0.008010519 0.008408262 0.007559825 0.006494972

P 0.16021038 0.336330468 0.453589488 0.519597736

Cp 0.063234968 0.143159894 0.192310515 0.213297133 0.230548758 0.236128638 0.224519356

At 6 m/s, λ 0 0.25 0.5 0.75 1

Cp 0.068524542 0.143853921 0.19400748 0.222240263

1.25 1.5 1.75

100 120 140

0.005637094 0.004828972 0.003971157

0.56370942 0.579476688 0.555962008

0.241107536 0.247851449 0.237793844

ω 0 26.66666667 53.33333333 80 106.6666667 133.3333333 160 186.6666667

T 0.01446539 0.014366756 0.015078755 0.013483683 0.011624316 0.010100424 0.008666423 0.007135509

P 0.383113493 0.804200267 1.07869464 1.23992704 1.3467232 1.386627712 1.331961699

Cp 0.069132846 0.145117972 0.194650494 0.223744887 0.243016259 0.250217029 0.240352545

T 0.022760614 0.022472945 0.02370392 0.021125459 0.018246039 0.015865623 0.013637553 0.011246979

P 0.749098167 1.580261333 2.1125459 2.4328052 2.6442705 2.7275106 2.6242951

Cp 0.069209066 0.146000105 0.195177795 0.224766503 0.24430375 0.25199429 0.242458226

T 0.032940932 0.03262114 0.033751621 0.03050053 0.026393546 0.022955622 0.019757694 0.01630959

P 1.3048456 2.70012968 3.6600636 4.22296736 4.5911244 4.74184656 4.5666852

Cp 0.06977784 0.144391961 0.195725326 0.225827132 0.245514674 0.253574682 0.244207765

At 8 m/s, λ 0 0.25 0.5 0.75 1 1.25 1.5 1.75

At 10 m/s, λ 0 0.25 0.5 0.75 1 1.25 1.5 1.75

ω 0 33.33333333 66.66666667 100 133.3333333 166.6666667 200 233.3333333

At 12 m/s, λ 0 0.25 0.5 0.75 1 1.25 1.5 1.75

ω 0 40 80 120 160 200 240 280

Cp vs λ

Effect of Drag forces: At 6 m/s, λ 0 0.25 0.5 0.75 1 1.25 1.5 1.75

D 0.37345641 0.37834384 0.41036625 0.37715865 0.3370608 0.31038735 0.28642996 0.26210378

Cd 0.958428379 0.970971346 1.053152789 0.967929707 0.865023675 0.796569658 0.735086063 0.672656016

D 0.66836777 0.67517844 0.73178179 0.66924164

Cd 0.9648441 0.974675865 1.056387478 0.966105604

At 8 m/s, λ 0 0.25 0.5 0.75

1 1.25 1.5 1.75

0.59984034 0.55212179 0.50928986 0.46592857

0.865919093 0.797033423 0.735201993 0.672606388

Cd vs λ

Effect of viscosity Table : Pitch 0.25 0.5 0.75 1 1.25 1.5

λ 1.5 1.75 1.75 1.75 1.5 1.5

ω(rad/s)

Torque

Torque

Cp

C

70 81.66666667 81.66666667 81.66666667 70 70

(pressure) 0.001047109 0.001199356 0.001455495 0.001607615 0.001864212 0.00191146

(viscous) 0.000321667 0.000375842 0.000387114 0.00038923 0.000348867 0.000346032

(pressure) 0.157945172 0.21106162 0.256136826 0.282906834 0.281196382 0.288323359

(v 0 0 0 0 0 0

1.75 2

1.25 1.25

58.33333333 58.33333333

0.002184988 0.002154671

0.00030991 0.000305815

0.274651703 0.270840949

Cp (Pressure)

Cp (Viscous)

Testing setup: The testing procedure is conducted in the wind tunnel rig available in the laboratory of Kathmandu University. The open suction type wind tunnel employed in this study has 25cm×25m as a cross-sectional area. The experimental model was placed in the one-third of the total distance of the wind tunnel. The ball bearings were installed in the frontward and backward of the blade shaft. Wind turbine model employed in this study was consisted with Archimedes spiral wind blade and a dc motor employed with pulley. The motor was mechanically assembled backward of Archimedes spiral wind blade through main shaft of wind turbine model. For the power coefficient calculation as a function of torque, the current

0 0

and voltage were calculated obtained from multimeter reading. In the case of high flow condition, to provide the stability of the spiral wind turbine model, the frame was constructed with a thick metal base. To investigate the approaching wind speed, anemometer was placed at the center of the wind tunnel. The experiments condition on the approaching wind speed were controlled from 3 m/s to 11 m/s with step of 1 m/s. In the case of 3m/s as wind speed, even though the generated power was not so sufficient, the generated maximum aerodynamic power with approximately 13.32 Watt through Archimedes spiral wind blade can be observed at 8.08 as angular velocity.

Wind

Maximum

Maximum

Velocity

Aerodynamic

Power

Power

Coefficient[%]

RPM

Angular

Tip

Velocity

Ratio

Speed

3 m/s 4 m/s 5 m/s 6 m/s 7 m/s 8 m/s 9 m/s

Conclusion When the in-flow velocity increases, the pressure difference becomes larger. The pressure difference is large at the blade tip but small at the root region. This means that most of energy can be extracted near the blade tip like a three blade HAWT. Through wind tunnel experiment, the higher output power as a function of rotational velocity than design specification was investigated successfully. And also power coefficient as a function of tip speed ratio with more than……% of Betz limit can be observed successfully. From this sense, aerodynamic conversion performance through Archimedes spiral wind turbine model employed in this study from wind energy seems to have very higher efficiency between the small wind turbine models. The performance characteristics of the Archimedes spiral wind turbine employed in this study shows the similarity with Modern multi-blade turbine. And

the maximum power coefficient as a function of the torque shows the similar that of Ideal Efficiency of Propeller-type turbine. Recommendation:

References Arman Safdari, K. C. (January 2015). Aerodynamic and Structural Evaluation of Horizontal Archimedes Spiral Wind Turbine. Journal ofClean Energy Technologies, Vol. 3, No. 1. Ho Seong Ji, Kyung Chun Kim, Dr. Joon Ho Baek, The aerodynamic method of the Archimedes wind turbine, drs. M. Mieremet, Msf May 27th ,2014. Ho Seong Ji, Joon Ho Baek, Rinus Mieremet, Kyung Chun Kim, The Aerodynamic Performance Study on Small Wind Turbine with 500W Class through Wind Tunnel Experiments, International Journal of Renewable Energy Sources, Volume 1, 2016 Kyung Chun Kim,