Aerodynamics of blade of HAWT

Aerodynamic Of Blade Of HAWT

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Wind

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Importance of Wind Energy

1. A country will become more self-sufficient by using

alternatives such as wind power.

2. No CO₂ emissions

3. Creates jobs

4. Can be used for charging batteries or can be combined

with a diesel engine to save fuel

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Fundamentals of Wind Turbines

• Wind Power: Conversion of wind energy into a useful

form of energy.

ex. wind turbine, wind mills, wind pumps

• Wind turbine: A wind turbine is a device that converts

kinetic energy from the wind into electrical power.

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A Typical HAWT

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Horizontal Axis Turbine

• This is the most common windturbine design. In addition tobeing parallel to the ground, theaxis of blade rotation is parallel tothe wind flow.

• Some machines are designed tooperate in an upwind mode, withthe blades upwind of the tower.

• In this case, a tail vane is usuallyused to keep the blades facing intothe wind. Other designs operate ina downwind mode so that the windpasses the tower before strikingthe blades.

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Horizontal axis wind turbine (HAWT)

• Rotor may be upwind or downwind of the tower.7

• Lift is the main force

• Much lower cyclic stresses

• 95% of the existing turbines are HAWTs

• Nacelle is placed at the top of the tower

• Yaw mechanism is required

HAWT

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Economic Advantages

• Greater fuel diversity

• No delay in construction

• Low maintenance costs

• Reliable and durable equipment

• Additional income to land owners

• More jobs per unit energy produced

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Airfoil Nomenclature

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Airfoil Shape

• Just like the wings of an

airplane, wind turbine blades

use the airfoil shape to create

lift and maximize efficiency.

The Bernoulli Effect

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Drag Force-“When an object place in the wind mill , it

experiences forces on the body. This forces are called as Drag

Forces.”

Lift Forces-“The force created due to pressure difference between

upper and Lower surface of the blade.”

• The forces on lower side is more than that on upper side

• For efficient operation lift must be more than Drag forces.

• The lift to drag ratio should be large for good operation

• Low pressure side of the blade is called as Aerofoil.

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Aerodynamic on Airfoil

Angle of attack-“The angle made between direction of wind and

chord line of the blade is called angle of attack.”

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Low Angle of attack Medium Angle of attack High Angle of attack

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Twist & Taper

• Speed through the air of apoint on the blade changeswith distance from hub.

• Therefore, tip speed ratiovaries as well.

• To optimize angle ofattack all along blade, itmust twist from root to tip.

Fast

Faster

Fastest

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Aerodynamic on Airfoil

p

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i

α

Aerodynamic Forces acting on Airfoil

• Where,

w- relative wind velocity

u- linear velocity or rotational velocity of blade

v- velocity of wind

FL- lift force

FD- drag force

F- total force

α- angle of attack

I – flow angle

i- pitch angle

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Aerodynamic Forces acting on Airfoil

• Consider a cross section of airfoil.

• Wind of velocity v acting on blade at point p as shown in

figure.

• Blade is rotating anticlockwise direction with velocity u.

• Take negative component u in a opposite direction a blade

rotation.

• This velocity component added vectorially to the impinging

wind velocity gives the resulting wind velocity, w.

• At right angle w, is the lift force FL caused by the

aerodynamic shape of the blade.

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Aerodynamic Forces acting on Airfoil

• The drag force, FD is parallel to the w.

• The vector sum of FL and FD gives resultant or total force,

F acting at point P due to wind as shown in figure.

• Now draw the projection line of vector, which states that

the total force acting in the direction of blade rotation.

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