How to average the torque coefficient for vertical axis wind turbine?

NotOverUnderated · March 13, 2021, 09:48

Hello,

I 've carried out a simulation in Ansys Fluent of the flow around a vertical axis wind turbine. I got the Cm (torque coefficient) as a function of time, hence azimuthal angle. I have used the rotor radius as the reference length, the swept area = diameter * height. In my case height = 1 because it's a 2D simulation.

Since the Cm coefficient is not constant over one rotor revolution, how to average it? because when I simply average:

$\overline{C_m} = \dfrac{\sum_{i=1}^{N}{C_{m,i}}}{N}$

And The average power:
$C_p = \lambda \overline{C_m}$

(where λ is the tip speed ratio).

The result is a very low Cp value. I have tried to run the simulation for several Tip speed ratios, but still, the Cp value is very low, less than 5%. (Unfortunately, I don't have experimental data to compare with).

I wonder if there is something wrong with the averaging of Cm. In VAWT nomenclature, how is the Cm value averaged?

I hope someone can give me insight.

Thank you in advance

chenxiaoxiao · August 24, 2022, 04:16

Quote:

Originally Posted by NotOverUnderated

Hello,

I 've carried out a simulation in Ansys Fluent of the flow around a vertical axis wind turbine. I got the Cm (torque coefficient) as a function of time, hence azimuthal angle. I have used the rotor radius as the reference length, the swept area = diameter * height. In my case height = 1 because it's a 2D simulation.

Since the Cm coefficient is not constant over one rotor revolution, how to average it? because when I simply average:

$\overline{C_m} = \dfrac{\sum_{i=1}^{N}{C_{m,i}}}{N}$

And The average power:
$C_p = \lambda \overline{C_m}$

(where λ is the tip speed ratio).

The result is a very low Cp value. I have tried to run the simulation for several Tip speed ratios, but still, the Cp value is very low, less than 5%. (Unfortunately, I don't have experimental data to compare with).

I wonder if there is something wrong with the averaging of Cm. In VAWT nomenclature, how is the Cm value averaged?

I hope someone can give me insight.

Thank you in advance

i have made some simulation like this, and find the same problem, in fluent , i can not get the real torque , maybe we should change the reference value

HHOS · September 6, 2022, 15:55

Hi,

I would simply write out to a file the total torque instead of the coefficient (given that it is not clear what it is doing). Then you can average as many timestep values as you want.

Regards

March 13, 2021, 09:48	How to average the torque coefficient for vertical axis wind turbine?	#1
NotOverUnderated Senior Member ONESP-RO Join Date: Feb 2021 Location: Somwhere on Planet Earth Posts: 127 Rep Power: 5	Hello, I 've carried out a simulation in Ansys Fluent of the flow around a vertical axis wind turbine. I got the Cm (torque coefficient) as a function of time, hence azimuthal angle. I have used the rotor radius as the reference length, the swept area = diameter * height. In my case height = 1 because it's a 2D simulation. Since the Cm coefficient is not constant over one rotor revolution, how to average it? because when I simply average: $\overline{C_m} = \dfrac{\sum_{i=1}^{N}{C_{m,i}}}{N}$ And The average power: $C_p = \lambda \overline{C_m}$ (where λ is the tip speed ratio). The result is a very low Cp value. I have tried to run the simulation for several Tip speed ratios, but still, the Cp value is very low, less than 5%. (Unfortunately, I don't have experimental data to compare with). I wonder if there is something wrong with the averaging of Cm. In VAWT nomenclature, how is the Cm value averaged? I hope someone can give me insight. Thank you in advance

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September 6, 2022, 15:55		#3
HHOS Member Join Date: Jul 2013 Posts: 98 Rep Power: 13	Hi, I would simply write out to a file the total torque instead of the coefficient (given that it is not clear what it is doing). Then you can average as many timestep values as you want. Regards