"Blade Design:Now, in the wake of achieving efficiency the design of the blades plays an importantrole. In order to understand the different methodologies involved in the designing ofthe blade, we shall first describe the composition of a blade.- Spar cap endures most of the force and bending moment acting on the bladebeing the main component of the blade; the size of the spar plays animportant role in deciding the blade mass and also the stiffness of blade. Italso influences the strength of blade. The effect of edge wise bending loads isrestricted by spars and internal webs. The edge wise bending loads arecarried by edges of the profile. 85- 90% of the load acting on the blade iscarried by the Spars, making it an indispensible part in the wind turbineblade.- There are different ways of designing shear web - either as a girder- structure, connected by one or two shear-webs or as a full box-like beamstructure. The performance demands on such load carrying structures aredirectly proportional to the length of the blade. The crucial element here isthe stiffness of the material in the structural beam as it prevents the bladefrom striking the tower when rotating.Cross Section:- The blade root is usually circular in cross section to connect to the pitchbearing the hub. The blades are fixed to the hub via a bolted connectionthat allows them to be removed. Most blade roots comprise of a thicksolid laminate with studs or T-bolts either screwed or bonded in. Thegrinder structure (or box section) of the load carrying spar must be joinedto the cylindrical laminate at the root. Normally this is done byincorporating a smooth curved transition area. Care must be takenduring the curing of the composite structure as the high thickness in thelaminate sections could lead to a build up of high exothermictemperature. (HEXCEL) Therefore many manufacturers make roots as a separate component. The bonding of this joint is critical andconcentration of stress in this area must be avoided.- The aerodynamic shape is formed by shells which are stiffened by using asandwich construction. Thin skins, usually of glass reinforced plastic, areplaced either side of a light weight foam core. The resulting sandwichconstruction is stiff enough to resist bending due to aerodynamicpressures and buckling. With diagonal fibres in the laminate, the shellprovides the blade with the necessary torsional stiffness. (Tony Burton,2011)Different methods for designing blades:- FEM (Finite Element Method) or Finite element analysis is a method fordesigning a blade. In this method, the whole body is divided into smallelements all the sections are analyzed for stress and loads acting on them.(Vipin Kumar Singh, 2013) Generally it is done in ANSYS. The FE-simulationusually predicts the global stiffness and stresses with a high qualityaccuracy. (Nitin Tenguria, 2010) FEM is extensively used to analyze complexload cases inheriting the actual wind conditions. Flap wise loading aregenerally analyzed by FEM.- CFD (Computer Fluid Dynamics) is a branch of fluid mechanics that usesnumerical methods and algorithms to solve and analyze problems thatinvolve fluid flows. It is used for prediction of aerodynamics and loadcharacteristics of wind turbine blade.- BEM (Blade Element Momentum) theoryAs explained in the work of (Manwell, 2009), “the momentum theory refers toa control volume analysis of the forces at the blade based on theconservation of linear and angular moment. Blade element theory refers toan analysis of forces at a section of the blade, as a function of the bladegeometry”. Both theories can be combined into what it is known as BladeElement Momentum (BEM) theory. The BEM extends the theory of theactuator disc incorporating the influence of the rotor blades. The effect ofeach elemental ring is defined by analyzing the aerodynamic response of theblades to the flow in which they are immersed.BEM is mainly used to predict the chord length and thickness of the blade.It also yields efficient information regarding the wind loads. All theaerodynamic forces acting upon the rotor blade can be efficiently measuredthrough BEM. A blade is divided into smaller elements and each element isanalyzed for the wind load. (Vipin Kumar Singh, 2013) The following assumptions are made:- There is no aerodynamic interaction between elements- The forces on the blades are determined by the lift and dragcharacteristics of the airfoil shape of the blade. Selection of a wind turbine profile is a key aspect for the wind turbine blade.Although BEM is very efficient in predicting the chord length and twist of theblade, yet it can give inaccurate results if the data is not corrected forrotational aspects. This is the reason that CFD is used for such analysis ofnew blade design. (Vipin Kumar Singh, 2013)Aerodynamic Analysis:In This section, we explain the rotor blade design parameters used to calculate itsaerodynamic performance.The wind turbine parameters considered in the design process are as follows:? Swept area? Power and power coefficient? Tip speed ratio? Blade chord? No. of blades? Solidity? Initial angle of attackSwept areaThe swept area is the section of air that encloses the turbine in its movement, theshape of the swept area depends on the rotor configuration. This way the sweptarea of the HAWT is circular in shape, while for a straight bladed vertical axis windturbine, the swept area has a rectangular shape and is calculated using:S=2RL2 Where S is the swept area [m ] R is the rotor radius [m]L is the rotor blade length [m]The swept area limits the volume of air passing by the turbine. The rotor convertsthe energy contained in the wind in rotational movement. So, bigger the area,bigger the power output in the same wind conditions.Power and power coefficientThe power available from wind for a vertical axis wind turbine can be found fromthe following formula: "