Design and Analysis of Vertical Axis Wind Turbine Blade

International Research Journal on Advanced Science Hub (IRJASH) 8 Design and Analysis of Vertical Axis Wind Turbine Blade A.J Sriganapathy, S Sudhan , T. Sundarmagalingam , E.Nijilabinash , T.Siva Assistant professor, Department of Aeronautical Engineering, Mahendra institute of engineering and technology, Tiruchengode, Namakkal. Tamilnadu, India. 2.3.4.5 UG Scholar, Department of Aeronautical Engineering, Mahendra institute of engineering and technology, Tiruchengode, Namakkal. Tamilnadu, India. Sri.aero87@gmail.com, Sudhansudhan2371998@gmail.com, Sundar51098@gmail.com, randynijil@gmail.com, Sivaking921@gmail.com Abstract Wind is used from a very long time as a source of electricity. Lots of efforts have been made to develop the horizontal axis wind turbines but vertical axis wind turbines did not get much attention over the past couple of decades. In the current era of energy crisis it has acquired more significance. Blade is the most important component of a wind turbine which controls a wind turbine 's performance and the design of other components that are attached to it. Current work introduces a concept for the design of a twisted unsymmetrical blade for a small-scale vertical axis wind turbine with beam theories for analytical modeling and a commercial program MSC NASTRAN, PATRAN for numerical modeling. The design parameters of the blade such as solidity, aspect ratio, pressure coefficient etc. are calculated with the goal of the 1 kW power output and the blade design was tested under extreme wind conditions where maximum deflection and bending stress values were calculated at peak aerodynamic and centrifugal forces values. Mainly the design considered achieving the structural strength i.e. reduction of deflections and bending stresses. This blade design has high strength and lower material consumption to achieve the low cost of complete wind turbine rotor assembly which actually covers over 50 percent of total wind turbine costs.


Introduction
Wind power is a form of solar power. Wind or wind power defines the mechanism by which wind is used for electricity generation. Wind turbines convert mechanical power to the kinetic energy in the wind. Mechanical power can be transformed into electricity by a generator Mechanical control can also be specifically used for particular tasks such as water pumping. Wind is caused by the uneven heating of the atmosphere by the variations in the surface of the earth and the earth's rotation.
The National Wind Technology Center (NWTC) is the nation's leading testing facility for wind energy technology. The goal of NWTC's research is to help the industry cut energy costs so that the wind can complete with traditional energy sources, providing a clean, renewable alternative for the energy needs of our nation. The bulk of the wind industry is actually dominated by horizontal axis wind turbines. Horizontal axis means the wind turbine's rotating axis is horizontal, or parallel, to the ground. Horizontal axis wind turbines are the dominant type of turbine for big wind farms or industrial customers. However, vertical axis turbines have a role in smaller or industrial wind applications.[1−4] The benefit of the horizontal axis is that it can actually generate substantially more energy from a given amount of wind. A downside of turbines with horizontal axes is that they are usually heavier and do not produce much power in turbulent winds. Hence their location plays a big part in how successful the turbine will be and how much energy it will generate. Vertical axis wind turbines, or VAWT, work differently, as the turbine 's rotational axis stands vertically or perpendicular to the ground. As previously mentioned, turbines with vertical axes are primarily used in smaller or residential installations. Wind coming from all 360 degrees drive the vertical axis turbines. In certain situations, when the wind is blowing from top to bottom, vertical axis turbines can be powered. Due to their versatility, wind turbines with vertical axes are thought to be ideal for installations where wind conditions are not consistent.[5−9].

Computational Fluid Dynamics Analysis
To help validate the results obtained from QBlade, a simple two-dimensional computational fluid dynamics simulation was carried out using ANSYS CFX. The two-dimensional analysis is not as accurate as a full three-dimensional analysis, but does allow for greatly reduced computational demands. The meshing setup is an essential part of a CFD analyze. Because the forces on the turbine blades (i.e., lift and drag forces) are guided by the effects of the boundary layer, the mesh around the blades must be fine enough to catch these effects with precision. The approximate boundary-layer thickness for a laminar flow is given by the following formula: (1) Where ∂ is the boundary-layer thickness, is the characteristic dimension (in this case, the position along the chord of the airfoil), and Reₓ is the Reynolds number in terms of the characteristic dimension. For turbulent boundary layers, the thickness is given by: (2) The thickness of the boundary layer on the VAWT blade from the leading edge to the trailing edge was calculated shown in the Fig.1.

Boundary Condition
To simulate an incoming wind velocity, an inlet boundary condition was placed at the upstream end of the stationary domain. This inlet has assigned a constant velocity. The opposite end of the stationary domain was assigned as an outlet, allowing flow to exit against atmospheric pressure. The simulation has refined to ensure that the outlet was sufficiently far downstream for the fluid wake to stabilize prior to exiting the simulation. The sides of the stationary domain were given .[3−6].a free-slip wall condition. This allows the fluid to move freely parallel to the wall, but requires that the velocity normal to the boundary be zero is shown in figure.3.

Solver Setup and Result
The solver was run for approximately 3 turbine revolutions, or at 35 RPM for 5 seconds. All domains were given an initial inlet velocity equal to that. It took the simulation about eight hours to run. Since the simulation is in two dimensions, the raw data per unit length is in terms of torque. To achieve the results below, the raw output was multiplied by the blade length of 20 metres. P=Tω Where P is the power, T is Torque and ω is angular velocity. At a wind speed of 10 metres per second and a rotational speed of 35 RPM, the average power output was approximately 140 kW. Applying a 96% efficiency to account for generator losses, the output becomes 134 kW.  In addition to operating at peak aerodynamic efficiency it is important to design a VAWT that can withstand lift forces, drag forces and wind loads. Structural analysis was performed on individual VAWT components because different loads were placed on each element.

Blade Structural Design
Structural blade design determines the cost of manufacturing a blade, load bearing capacity and hence overall structural performance (in terms of reliability and robustness). Extreme loading analysis (i.e. tip deflections and buckling) accompanied by fatigue and modal analysis is the latest state of the art for structural blade design in terms of criticality; In blade design process, fabric (laminate) and inter-fibre failure (static strength analysis) along with aero-elastic stability (such as flutter) play a secondary role. Laminates consist of different ply layers of fibers stacked in a specific direction on top of one-another.

Analysis and Methodology
This part of the report deals with the procedure and approach used for calculating aeroelastic loads (briefly), blade layout for Finite Element Analysis ( FEA) and various branches of rotor blade computer modeling with special emphasis on Fatigue.

Blade Analysis
A typical blade of airfoil cross-sections is composed of fig.6 .. Within the blade is strengthened to preserve the airfoil's original shape during service. The airfoil parts belong to the rest of the blade, and the aerodynamic efficiency is determined. Selecting suitable cross-section shape, taper angle, and twist angle plays an significant role in maintaining aerodynamic forces. A complete methodology for selecting the blade geometry, profile, and dimensions is described in this section when designing it for the required power output.

Internal Structure
The internal structure is shown in fig.7 is conceived to obtain maximum strength with the least weight; The spars are the most important structural component of the wings, since they carry the airloads during blade rotation. Blade has a Box spars is placing at 40% of blade chord which acting as the structural reinforcement for the blade to be more efficient at resisting out-ofplane shear loads and bending moment. The Blade has a chord of 0.28m; the spar is placing at 0.112m from the leading edge of blade with respect to centre position of spar.

Twisted Unsymmetrical Blade
The unsymmetrical vertical axis wind turbine blade is designed with angle of twist which is shown in Fig.8. This design is mainly considered to reduce the deflection and bending stress. To reduce the amount of material, it was important to minimize the thickness and withstand the worst possible wind loads.
Bending, axial and shear stress analyses were performed to determine if these dimensions and material are suitable.    Fig.15 shows the stress analysis for aluminium and composite.

Conclusion:
The object of this project has to design a Maui, USA, 2011.