Aerodynamic calculation of loads and dynamic behavior of wind ...

1. Maximum frequency of time histories
2. Discretization in the frequency domain
3. Maximum time period for each time history
4. Discretization in the time domain
5. Number of points along each blade, at which the wind velocity will be
calculated
6. Azimuth angle discretization
The second step requires from the user to provide the characteristics of the wind
turbine in question. These are the:
1. Wind turbine rotational speed 3
2. Blade radius
3. Number of blades
4. Hub height
5. Tower diameter 4
6. Blade - tower clearance
7. Air density
8. Blade chord variation along the blade
9. Pitch angle variation along the blade 5
10. Lift coefficient for each possible angle of attack 6
11. Drag coefficient for each possible angle of attack
The third step of the algorithm consists of all these commands necessary for the
generation of the wind-velocity time histories. The program is based on the theory
presented and analyzed in Chapter 2 and utilizes the information given by the user in
step 1.
The final part takes as input the resulting wind-velocity time history, produced in
the previous step, along with the wind turbine characteristics from step 2, and
calculates the loads exerted on the blades and, therefore, on the turbine’s tower, by
simulating the concepts described in Chapter 3.
4.3 Accuracy of the algorithm
At this point, a necessity arises for an assurance, regarding the accuracy of the
created algorithm. A relatively appropriate way to evaluate the results of the program
is to compare them with those of the references. The following comparative
diagrams, referring to the various parameters that characterize the function of a wind
3 This implies that the rotational speed of the wind turbine remains constant, regardless of the
wind velocity. However, in order to produce the highest possible power, modern wind turbines change
their rotational speed depending on the wind velocity, as to maintain a desirable tip-speed ratio.
4 In fact, the diameter of the tower varies with height. In order to take the tower shadow effect
into account, however, only the diameter at the top matters. Therefore the required information refers
to that value.
5 Ideally, a wind turbine has to continuously alter the pitch angle along the blades, depending on
the attack angle, which, in turn, depends on the wind velocity.
6 In fact, it is impossible to provide lift and drag coefficient values for every possible angle of
attack. Thus, the alogorithm uses the technique of linear interpolation to determine the coefficients for
angles not included in the tables.
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