Wind Energy Laboratory (part 2)


Amirkabir University of Technology


Cp-landa curve of Wind Turbines

Lift type wind turbines are widely used in modern wind energy conversion systems. 

The blades in these types of wind turbines are very similar to the wings of an air plane. 

The lift forces are generated by different air pressures between the upper side and the lower side of the blades, and rotate the blades. 

The rotating forces ( red lines on above figure ) would generate rotational torques.  The sum of all rotational torques is the total rotating torque.  This torque ( t ) depends on the wind speed ( V ) , the pitch angle of the blades , and the rotational speed of blades ( w ). 'V', the wind speed is assumed to be constant over the surface area (the blade generated circle).

The torque multiply by 'w' is the power. hence the 'P' vs. 'w' curve can be introduced;

The efficiency of a wind turbine is the mechanical power generated divided by the power of the wind available at the hub.

That is; 'Pmech.'/[1/2 r A V^3}.  The efficiency is known as power coefficient, 'Cp'; Because 'w' and 'V' are both variable, there are more

 than one curve involved.  The curves can be converted to one curve, using a parameter known as 'Tip Speed Ratio' or 'l'.

'l' can represent a point of reference for the resultant of all angles of attacks.

only the wind turbine image extracted from; ref:

This results in one curve; Cp vs 'l'.

Variable pitch results in more than one cp-l curve;




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