This is part 3 of my series: "How Does a Wind Turbine Work?" In this video I show you how to use the blade element momentum theory, BEM, that we discussed in the previous videos to design an efficient wind turbine rotor.

Topics include:
00:33 Elevator Comparison
00:47 Optimal aerodynamic conditions with constant circulation along the span
01:05 How local wind speed and angle vary over the length of the blade
01:22 How to change the chord and twist angle along the blade span
01:50 Why designers normally adjust the chord division to have smaller chords at the root
02:28 The torque equation and why tip aerodynamics are more important than the root
02:52 What happens if you use a turbine at a different wind speed than it was designed for?
03:46 How variable speed turbines can operate efficiently across a range of wind speeds
04:18 What is tip speed ratio (TSR) and why is it important for wind turbine designers?
04:48 Firmness of the blade
06:07 How do you find a starting point in the design process of wind turbine blades?
07:22 Why are wind turbine blades getting so thin?
07:54 Reducing wind turbine noise by limiting rotation speed
08:29The different requirements for airfoils at the base versus the tip of the blade

Check out parts one and two of my series "How Does a Wind Turbine Work?" where I go through the mechanical engineering and aerodynamics theory needed to understand how a wind turbine works and to design a wind turbine blade:
How much energy is in the wind?
https://www.youtube.com/watch?v=7-awFXqisYA&t=7s
How to Calculate Wind Turbine Power: Blade Element Momentum Method
https://youtu.be/o6BCnhubbiQ

If you would like to follow the derivations I mentioned in this video, please see section 3.7.2 of Burton's /"Wind Energy Handbook./"
Available through Amazon (affiliate link), and your university library probably has it too!
https://amzn.to/32Pb1fh

The optimal aerodynamic design equation at 6:10 has the following parameters:
sigma_r = chord strength at the radial location (chord length divided by the circumference of the circumference at that radial location)
lambda = tip speed ratio (tip speed due to blade rotation (radial location times rotation speed) divided by wind speed)
C_l = local lift coefficient
mu = r/R (radial location divided by radius)

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