Arjstte 02 003

Advanced Research Journals of Science and Technology

ADVANCED RESEARCH JOURNALS OF SCIENCE AND TECHNOLOGY

(ARJST)

AERODYNAMIC ANALYSIS OF NACA 4315 AIRFOIL WIND TURBINE BLADE FOR POWER CALCULATION USING BETZ LIMITING THEORY

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Rasamsetti Siva Manga Jyothi1, V.V. Ramakrishna2, I.Manoj Krishna3, 1Research Scholar, Department of Thermal Engineering,Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

2 Associate ProfessorDepartment of Mechanical Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

3 Associate ProfessorDepartment of Mechanical Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

Abstract With an increase energy crisis around the world it is important to investigate aiternative methods of power generation in ways different than fossil fuels . few of the energy sources available all around the world at all times “wind and solar”. In this thysis wind generation is concentrated up on . the major aerodynamic properties of wind turbine were studied. The wind that cuts the wind turbine blade flows through its cross section lie on aerofoil plays an important role in power generation . so the aerodynamics of NACA 4315 aerofoil were studied. In anysis fluent an artificial wind turbine was created around the aerofoil, the inlet conditions were given the flow of the air is taken as laminar as it could decrease the complications in the results. The amount of power generated by a blade of infinite length having the profile NACA 4315 was calculated using the BETZ limiting theory. *Corresponding Author: Rasamsetti Siva Manga Jyothi , Research Scholar, Department of Thermal Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

Published: December 28, 2015 Review Type: peer reviewed Volume: II, Issue : II Citation:Rasamsetti Siva Manga Jyothi,Research Scholar(2015) AERODYNAMIC ANALYSIS OF NACA 4315 AIRFOIL WIND TURBINE BLADE FOR POWER CALCULATION USING BETZ LIMITING THEORY

INTRODUCTION Motivation: India contributes around 1.8% of the total global CO2 emission. The global CO2 emission estimated by International Energy Agency in 2010 is 30.6 Gigatonnes from which india contributes about 1.67metric tons which is 5 % more than the earlier record which was estimated in 2008. Around 80% of this emission is from the power sector. (International Energy Agency 2011) With the major energy sources diminishing the world is looking for more and more renewable and zero emission energy sources like Solar energy, wind energy, tidal energy, biomass etc.

One of the most important sources of renewable energy is wind power. On Wind energy noted American author and Naturalist Henry David Thoreau said that “First there is the power of wind, constantly exerted over the globe. Here is an almost incalculable power at our disposal, yet how trifling the use we make of it.” (Jain 2011) This is done by using wind turbines to extract kinetic energy from wind.

In comparison with other renewable resources Wind energy is a profuse resource. Climate and weather could affect the utilization of wind energy when compared to solar energy. In order to get energy from the wind, wind turbines

were invented. The wind turbine converts the wind energy into electrical energy and is also called as wind generator.

The use of wind energy is growing rapidly in developed countries. In India wind power began in the year 1986, the first wind farms setup in coastal areas of Gujarat, Maharashtra, and Tamil Nadu with 55KW wind turbines. The present wind power in India is estimated as 24677MW as on 31st October 2015. Floating wind turbine technologies in deep sea areas is under implementation.

The main purpose of the project is to study the various designs of wind turbine blades. A lot of research is being done in blade aerodynamics which increases the energy capture thereby maximising the power production (Robinson, 2007). One of the first wind turbine developed by Poul La Cour to generate Electricity in Denmark had a rotor with four shutter sails. This four shutter sails rotor was used till a company named F.L Smidth developed an aerodynamic design of the rotor with two profiled rotor blades made of laminated wood for their wind turbine Aerometer. They worked on the concept of blade tip speed ratio which is the ratio blade tip speed to relative wind speed (Hau, 2006). So attention will be more to increase the blade tip speed ratio to increase efficiency of the turbine without causing disturbances due to increase in noise levels.

Aim: The aim of this project is to study and Analyze an aerodynamics of different wind turbine blades and to evaluate the smallest possible properties affecting the power output of the turbine..

Objectives: • Formulate the basic principles and theories used in design of wind turbine blades like moments theory, BETZ theory.

• examine the properties within the blade which affect its output power.

• Develop a product design specification table on which the aerodynamic analysis would be performed.

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Advanced Research Journals of Science and Technology

• Based on mathematical relations and calculations from literature survey aerofoil design is developed Using a CAD software • Using fluent CFD software replicate the air flow around the aerofoil and compute the power generated.

• Investigating the aerodynamic design of the blade by testing it in a wind tunnel and calculate the values of lift and drag for the observation. Compare the results from wind tunnel with the results in the standards.

• Produce a report documenting all the research and activities undertaken during the course of project.

Research Methods: The Research work done in this thesis is divided into three parts.

The curve for the aero foil

In the first part the research is done by studying the standards, patents and journal articles. The data is collected from those files. The fundamental relations are derived from the literature that was available.

In the second part a model of aerofoil section was designed on the software using these relations. This design was used to create a prototype using a Rapid Prototype machine and the prototype was tested in a wind tunnel to calculate the lift and drag properties at different wind speeds and at different angle of attack.

The curve as a closed body

In the third part the aerofoil design is used to stimulate the airflow around the aerofoil using a CFD software (Ansys-Fluent) and understand the phenomenon of Lift and Drag. Using the velocity and pressure contours generated

by Fluent for the airflow around the aerofoil the percentage of the kinetic energy of the wind converted into mechanical output is calculated.

Methodology: Flow of Fluid around a Wind Turbine Blade: When a fluid flows through a wind turbine blade it’s cross-section(Aerofoil) cuts the flow of the fluid. So for discussing flow of fluid through a wind turbine blade we have to study the flow of fluid around the aerofoil in 2-D. The speed of fluid flow on the surface is zero. The region around the surface where the speed increases to reach free stream velocity is called Boundary Layer. (Jain 2011) The fluid forces on the aerofoil can be resolved as normal and streamwise forces. The normal forces (lift) rises when buoyancy is neglected because of the fluid mechanics. The drag forces depend on the boundary layer of the fluid. (Buton 2001)Here the Coefficient of Lift, Drag and Moment on the aerofoil are studied in the wind turbine to study the aerodynamic properties of the blade aerofoil at different Reynolds number and angle of attack. While Reynolds number is related to chord length of the aerofoil and wind speed.

Aero foil prepared by extrusion of the curve

Image showing the hole cut in the aero foil

Rapid Prototyping of the Model:

These observations are made by testing a prototype of the aerofoil section of a finite span in a wind tunnel.

The process starts with designing the model in CAD software and saving it as STL file which means stereo Lithography (cooper 2001). These STL files are sent to the pre-processor which checks the files and then transfers it into. The STl file represents the solid model in triangulated portrayal. The design developed in solidworks is given as input in the rapid prototype machine. The process was 32

Advanced Research Journals of Science and Technology

completed in 8 hours and the prototype was kept in solution to remove the supporting material on it. The plastic used for making this prototype was Acrylonitrile Butadiene Styrene (ABS) though this does not have much effect on the result as we are studying the aerodynamic properties of aerofoil and it does not depend upon the material. Due to the layer- layer fabrication the surface of the aerofoil produced is rough and has many lines on it. So to make the surface the soft the surfaces were rubbed with wet and dry paper of grades 240 and 320 and then the aerofoil is spray painted to make its surface smooth. The prototype is now ready for the wind tunnel test.

The relations used to compute the values of the velocities at these three positions are

The difference between levels of the manometer tubes fitted to wind tunnel help to calculate the pressure difference.

Wind Tunnel Test:

Prototype placed in the wind turbine

A subsonic wind tunnel is used in this experiment. A wind tunnel is a test rig based on ground designed to test the flow of air or different gases around the particles. A low speed subsonic wind tunnel work under the conditions when Mach number less than 1 (Anderson 2008).

For subsonic wind tunnels Ma < 1, the value of Ma is calculated using the formula.

Ma= V/a Where V is the flow velocity at the section, A is the speed of sound. (Anderson 2008) A schematic of the subsonic Wind tunnel is shown in the figure.

Wind Turbine AF 100

Schematic Representation of wind tunnel

Here the test area is converged to increase the velocity and to decrease the pressure the mach number increases till it becomes. When it becomes 1 it will decrease as the air enters the diverging diffuser decreasing the velocity and Mach number. (National Aeronautics and Space Adminstration 2011)

Image showing wind turbine test section

Simulation of Airflow around the Airfoil using Computational Fluid Dynamics.

A fluid volume and mesh was created around an airfoil for analyzing in the fluent. â&#x20AC;˘ Created a non symmetric 4315 airfoil. â&#x20AC;˘ Choose points to 60 and point size to 4 to ensure that the points are clearly visible.

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Advanced Research Journals of Science and Technology

Aero foil inside an artificial wind tunnel designed in ANSYS

L/D vs Angle of attack for Re number 5E4

Plot of Coefficient of Lift Vs Angle of Attack: The plots for Cl vs. angle of attack indicate that the coefficient of lift of the aerofoil increases rapidly till a particular angle and then starts to decrease gradually. This phenomenon is called stall and the angle at which the stall starts is called stall angle. The angles of the different Reynold’s number at which stall occurs are 14°, 15° and 15°.

The boundaries meshed around the aero foil

Plot of L/D ratio or Sliding Rate Vs Angle of Attack: The plots for L/D vs angle of attack show results where the range of angle of attack is from -8 to +12. The graph shows that the L/D value increases till a particular value which is the optimum angle of attack and starts to fall beyond that which is knows as stalling.

For the Reynold’s number 100,000 the optimum angle of attack is 4 degrees.

For the Reynold’s number 70,000 the optimum angle of attack is 3 degrees.

Coefficient of lift vs Angle of attack for Re number 1E5

L/D vs Angle of attack for Re number 1E5 Coefficient of moment vs Angle of attack for Re number 7E4

Comparison with the NACA Results NACA has not studied the properties of 4314 but in their research of 78 aerofoils NACA 4312, 4315 are researched and studied .The figure below shows the plots for NACA 4312, NACA4315.

4.2 Fluent Results: In fluent the boundary conditions given were, angle of attack was set zero, inlet velocity 10m/sec and all the three sides were chosen as the inlet with the side of the leading 34

Advanced Research Journals of Science and Technology

edge chosen as the outlet. The boundary layer was chosen as the lamina, because if the turbulent flow was selected, there would have been a number of complex equations defining the flow so for just a test purpose the lamina flow was selected. The results were processed and were displayed as the counters of pressure and velocity. Here using the counters of the pressure and velocity it can be indicated that the velocity at the leading edge of the aerofoil is nearly equal to 0 and the velocity on the upper surface of the aerofoil is maximum and the value is equal to 1.13.101m/sec. As the velocity of the air at the leading edge is nearly 0, this increases the velocity of the air around the aerofoil. As the lower surface is a bit flat when compared to the upper on the velocity isn’t as high as the upper surface. These velocities converge at a distance away from the trailing edge. At this distance a zero velocity area is created which is called vortex. As the velocity of the upper surface is higher the pressure on the lower surface is higher, this generates the lift as the pressure evens out from lower surface to higher surface. The maximum pressure is found at the leading edge of the aerofoil which is equal to 6.1x101N/m2

Velocity Contour

Conclusion According to the research the major aims and objectives of this project which were achieved are listed below - The major aerodynamic properties of a wind turbine were studied - The wind that cuts the wind turbine blade flows through its cross section(i.e. an aerofoil) which plays an important role in power generation, so the aerodynamics of different aerofoils were studied - NACA 4315 aerofoil was selected to do the research and it was worked on both software(ANSYS-Fluent) and as well as in practical in a wind tunnel - The wind tunnel test gave the values of life and drag at different angles of attack on different Reynolds’ number - These values were plotted and they were compared with the plots developed by NACA in their technical reports

Stream lines showing air flow around the aero foil

- The plot results showed similar results as to the original ones released by NACA but the magnitude of the research values were less in comparison to the originals.

- After a brief research the fact that came to light is that the NACA used high Reynolds’ number when compared to the ones used in this project - The Reynolds’ number depends upon the chord length and the wind velocity, the wind velocities used here were 5,7 and 10 m/sec which mimicked the wind velocity in and around the UK - From the plots it was noticed that the coefficient of lift increases with increase in angle of attack till a certain value and begins to decrease as well as the coefficient of drag increases, this condition is called stall

Stream line showing the air flow around aero foil

- In ANSYS-Fluent an artificial wind turbine was created around the aerofoil, the inlet conditions were given, the flow of the air is taken as lamina as it could decrease the complications in the results - The mechanism of the lift and drag of the aerofoil were explained using ANSYS, the pressure drop and increase in velocity on the upper surface, were explained using the counter plots - The vortex at the tip of the blade was identified and the its area increases with increase in angle of attack

Pressure Contour

- The amount of power generated by a blade of infinite length having the profile NACA 4315 was calculated using the BETZ limiting theory.

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Advanced Research Journals of Science and Technology

Recommendation for Future Work This project was done in two dimensional methods and airflow around an aerofoil was analyzed. Though this was really a hard work with limited resources for a thesis, But for a research work on aerodynamics the analysis of a blade in a 3-dimensional method should be done. The blade should be designed considering the factors; blade twist, length of the blade, etc. the blade should have different aerofoils at different sections; for example; the tip of the blade should have the thinnest possible aerofoil while the hub shouldâ&#x20AC;&#x2122;ve the aerofoil the thickness of which should be very large when compared to the tip to avoid vibrations. Only the coefficient of lift and drag on different angles of attacks was studied in this thesis, different analysis of far field flow Yaw angle, stall control should be considered. The vibration problem should be discussed if a blade is considered instead of an aerofoil. The failures for the wind turbine blade should be discussed and the causes of the failures should be researched and analysed using finite element methods. Lists of failures that have occurred in recent years are mentioned in the appendix.

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Author

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Rasamsetti Siva Manga Jyothi, Research Scholar, Department of Thermal Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

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V.V. Ramakrishna Assistant Professor, Department of Mechanical Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

I.Manoj Krishna Assistant Professor, Department of Mechanical Engineering, Kakinada institute of technology and sciences, Divili,Andhra pradesh,India.

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