Dear all,
thank you for your posts which helped me a lot to calculate the aerodynamic coefficients for different pitch angles. I used the FAST model input file which Rannam suggested on 15 March 2012.
Assuming wind speed to be constant (v_w =8m/s), a Tip Speed Ratio (TSR) of 5 to 10 (step 1) and Pitch angle -5.0 deg to 9.0 deg I run a simulation with FAST. As a result, I got pretty much the same results for power coefficient obtained by FAST as Rannam posted on 14 March 2012. Hence, I assume that there should not be anything wrong.
However, I faced a problem related to thrust coefficient cT. The problem came up doing a simulation with FAST for:
Pitch Angle: 0.0 deg
Wind Speed: 3.0 m/s to 25 m/s (step 1m/s)
Rotor Speed: 1.0 rpm to 15.0 rpm
You will find the results attached.
The problem is the following:
For the same TSR I should get the same thrust coefficients (as far as I understand the meaning of thrust coefficient right). But this is not the case.
For example: For a wind speed of 3.0 m/s and a rotor speed of 1 rpm TSR= 2.20. The resulting cT=1.515.
For a wind speed of 6.0 m/s and a rotor speed of 2 rpm TSR is also equal to 2.20. However, the resulting cT=0.492.
Does anyone of you know what could be wrong in this simulation? These results were generated with the same FAST input file as mentioned above. As the results of power and torque coefficient were quite reasonable, I wonder why thrust coefficient is so strongly deviating.
Thanks in advance!
Sebastian Hippel
cT_P0deg.xls (49 KB)