SEMINAR ON

DESIGN OF WIND TURBINE BLADE

SUBMITTED BY: K.VENKETESH

31506209

NATIONAL INSTITUTE OF TECHNOLOGY KURUKSHETRA

INTRODUCTION OF WIND TURBINE:A Wind turbine is a device which converts kinetic energy from the wind into useful work.Smaller turbines are used for application of battery charging for auxiliary power boats, slightly larger turbines are used in domestic power supply.Bigger turbines are increasing important source of renewable energy and is a strategy to reduce reliance on fossil fuels.So in many countries wind turbine is a widely used to produce power from wind which is abundantly available in nature.

TYPES OF WIND TURBINE:HORIZONTAL AXIS:In horizontal axis wind turbine the main rotor shaft and electric generator at the top of the tower and must be pointed into the wind. And have a gear box which converts low speed to high speed.

VERTICAL AXIS:Vertical axis turbines have the main rotor arranged vertically. Turbine need not point to the wind to be effective. Generator and gear box placed near the ground.Low speed of the rotor.High cost of drive train.Dynamic loading in each cycle resulting to fatigue failure.

DESIGN OF WIND TURBINE BLADE:Before designing wind turbine blade following thing

must be taken into account:

Types of structural load.

Types of stress generated due to load.

Material needed to withstand the load.

Maximum strain and tip deflection.

Cost of the turbine blade.

STRUCTURAL LOAD ANALYSIS

Flap wise bending – Result of aerodynamic loads. It is therefore efficient to place load bearing material in the spar cap region of the blade at extreme portions from the central plane of bending.

Edgewise Bending -The edgewise bending moment is a result of blade mass and gravity.

Fatigue loading – Fatigue loading is a result of gravitational cyclic loads, which are equal to the number of rotations throughout the lifetime of the turbine.

SECTIONAL VIEW:

Cross section of a blade with references to the airfoil shell, spar flanges and shear webs :1, 2 and 3 respectively.

MATERIAL SELECTION:

•Needs –lightweight and high stiffness, hence composites.•Wood/laminates•Glass fibre laminates•Carbon fibre laminates

STEEL-Heavy and expensiveAluminium Lighter weight and easy to work withExpensiveSubject to metal fatigue due to cycilc loading.

CALCULATION OF WIND POWER:Power in the Wind = ½ρAV3

– Effect of swept area, A– Effect of wind speed,

V– Effect of air density,

Swept Area: A = πR2 Area of the circle swept by the rotor (m2).

BETZ LIMIT:All wind power cannot be captured by rotor or air would be completely still behind rotor and not allow more wind to pass through.

Theoretical limit of rotor efficiency is 59%

Most modern wind turbines are in the 35 – 45% range

R

Solidity = 3a/A

ROTOR SOLIDITY:Solidity is the ratio of total rotor planform area to total swept area.Low solidity (0.10) = high speed, low torque.

High solidity (>0.80) = low speed, high torque

Number of Blades – One• Rotor must move more

rapidly to capture same amount of wind– Gearbox ratio reduced– Added weight of

counterbalance negates some benefits of lighter design

– Higher speed means more noise, visual, and wildlife impacts

• Blades easier to install because entire rotor can be assembled on ground

• Captures 10% less energy than two blade design

• Ultimately provide no cost savings

Number of Blades - Two• Advantages &

disadvantages similar to one blade

• Need shock absorbers because of gyroscopic imbalances

• Capture 5% less energy than three blade designs

Number of Blades - Three• Balance of gyroscopic

forces• Slower rotation

– increases gearbox & transmission costs

–More aesthetic, less noise, fewer bird strikes

Airfoil ShapeJust like the wings of an airplane, wind turbine blades use the airfoil shape to create lift and maximize efficiency.

The Bernoulli Effect

FAILURE CRITERIA:1) TIP FAILURE: The tip deflection criteria requires that

a minimum 30% clearance of the static tower to tip distance maintained for turning tower and 5% for parked condition. The maximum tip deflection during the (EWM) load conditions was limited 11.48m.

2) BUCKLING FAILURE: The buckling study required a 1.634

safety factor, meaning that the structure must be capable of withstanding 1.634 times the worst case buckling condition.

The maximum and minimum strain criteria were used to verify that no elements in the model exceeded the design strains of the material. The material design strains were determined from the partial safety factors for the loads and the combined partial safety factors for the materials. The partial safety factor for the material based on short term (static) verification was found to be 2.205. The partial safety factor for aerodynamic loads was defined as 1.35 in for normal and extreme loading conditions.

3)MATERIAL STRAINS:

SUMMARY OF STRUCTURAL DESIGN AND ANALYSIS:The blade length determines how much wind power can be captured, according to the “swept area” of the rotor disc. Of all the energy in the wind, only about half can realistically be extracted (Betz’s limit).

The blades have an aerodynamic profile in cross section to create lift and rotate the turbine .

Typically the rotational speed chosen so that the tips are moving at seven to ten times the wind speed, and there are usually no more than three blades.

To maintain optimum angle of attack of the blade section to the wind, it must be twisted along its length

Primarily the blade is loaded in bending, due to the aerodynamic lift forces (flapwise) and to a lesser extent the blade’s own weight (edgewise). To resist bending, unidirectional fibres running along the length of the blade are placed as far apart as possible in the flapwise direction .

The aerodynamic shape is formed by shells which are stiffened by using a sandwich construction. Thin skins, usually of glass reinforced plastic, are placed either side of a light weight foam core. The resulting sandwich construction is stiff enough to resist bending due to aerodynamic pressures and buckling .

Glass fibre reinforced laminates offer good strength to weight ratio. Carbon fibre is more expensive but much stiffer and stronger, so tends to be used for the spar caps of longer blades.

REFERENCES:•WIKIPEDIA

•FLUID MECHANICS BY MODI AND SETH

•WIND TURBINE BOOK BY E .HAU

Thank you