Aerodynamics of blade of HAWT

different force acting on cross-section of blade..

1. Aerodynamic Of Blade Of HAWT 1

2. Wind 2

3. Importance of Wind Energy A country will become more self-sufficient by using alternatives such as wind power. N o CO₂ emissions Creates jobs C an be used for charging batteries or can be combined with a diesel engine to save fuel 3

4. 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. 4

5. A Typical HAWT 5

6. Horizontal Axis Turbine This is the most common wind turbine design. In addition to being parallel to the ground, the axis of blade rotation is parallel to the wind flow. Some machines are designed to operate in an upwind mode, with the blades upwind of the tower. In this case, a tail vane is usually used to keep the blades facing into the wind. Other designs operate in a downwind mode so that the wind passes the tower before striking the blades. 6

7. Horizontal axis wind turbine (HAWT) Rotor may be upwind or downwind of the tower. 7

8. 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 8

9. 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 9

10. Airfoil Nomenclature 10

11. 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 11

12. 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. 12 Aerodynamic on Airfoil

13. Angle of attack- “The angle made between direction of wind and chord line of the blade is called angle of attack.” 13

14. Low Angle of attack Medium Angle of attack High Angle of attack 14

15. Twist & Taper Speed through the air of a point on the blade changes with distance from hub. Therefore, tip speed ratio varies as well. To optimize angle of attack all along blade, it must twist from root to tip. Fast Faster Fastest 15

16. Aerodynamic on Airfoil p 16 i α

17. Aerodynamic Forces acting on Airfoil Where, w- relative wind velocity u- linear velocity or rotational velocity of blade v- velocity of wind F L - lift force F D - drag force F- total force α- angle of attack I – flow angle i- pitch angle 17

18. 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 F L caused by the aerodynamic shape of the blade. 18

19. Aerodynamic Forces acting on Airfoil The drag force, F D is parallel to the w. The vector sum of F L and F D 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. 19