**3. VAWT aerodynamics**

## **3.1 Aerodynamic airfoil and blades**

An airfoil is identified using its aerodynamic parameters [5] as shown in **Figure 1**. The mean curve line is the focus midway points between the upper and lower surfaces of the airfoil. While the straight line connecting the leading and trailing edges is called the airfoil chord line, and the distance from the leading edge to the trailing edge measured along the chord line is known as the aerodynamic airfoil's chord (c). Finally, the angle of attack, α, is defined as the angle between the relative wind (Urel) and the chord [6].
