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CT and CTy value calculation
I was doing a HAWT simulation for various yaw angles[0,5,10,15,20,25] and various tip speed ratios[4,5,6,7,8]. The simulation run time was for 0.1 second. I did get the CT value for each simulations. The problem is that the documentation of Qblade says CT = 4a(1-a) where a is the axial induction. If I try to find the value of a, there are 3 blades each with PAN 0-19, therefore I cannot find it.
I also tried using the formula, CT=8*Thrust/(pi*air_desnity *wind_speed^2 *rotor_dia^2). This formula gave me the value for CT almost similar to that of simulation result. But in case of yaw 20 and 25, the value are not close as before.
I used the thrust force by taking its average in the last revolution.
My ultimate goal is to calculate the CTy ( cross- stream thrust component). I was thinking if I can use the same CTy=8*Thrust_in hub_y_direction/(pi*air_desnity *wind_speed^2 *rotor_dia^2). But since this formula did not work in case of CT, I wonder if it will work in case of CTy also.
Hi,
the UBEM (unsteady Blade Element momentum Method) that QBlade is using is detailed in the following publication by researchers at DTU:
Helge Madsen, Torben Larsen, Georg Pirrung, Ang Li, and Frederik Zahle. Implementation of the blade element momentum model on a polar grid and its aeroelastic load impact. Wind Energy Science, 5:1–27, 01 2020. doi:10.5194/wes-5-1-2020.
In practice, we evaluate the induced velocities over radial annuli at each blade station. However, the exact formulation linking induction to thrust varies between different BEM implementations. For the complete derivation and implementation details, please refer to the publication cited above.
BR,
David
