## Fluids

#### Torque increases as rotational speed increases

• motoyama
Subscriber

Hi everyone,

I simulate two blade wind turbine with MRF.

but as rotational speed 'omega' increase, torque also increase.

so there is no peak on power coefficient.

How can I calculate it?

Ansys Employee

Hi,

How are you calculating torque?

Ansys Employee

Hi

How are you calculating torque? Please give more details. Please insert some images and explain the problem.

In general, you can do following to calculate torque.

Regards,

Keyur

Ansys Employee

Sorry post is giving some error to me.

1) Click “Report → Force” to open the Force Reports panel

Ansys Employee

2) In “Options”, select “Moments”

Ansys Employee

3) Enter the coordinates of the center point of the rotation for “Moment Center” and the axis at “Moment
Axis”

Ansys Employee

4) Select the Wall Zones

Ansys Employee

that will serve as the plane of rotation from where the torque will be calculated

5) “Print” will show the results in the Console Window

Ansys Employee

I am really sorry, I am getting some errors while posting it. May be some maintenance work is going on.

Hope you can read these posts.

Regards,

Keyur

• motoyama
Subscriber

I know the procedure.

but I've already checked the reference values, no problem.

and moment itself converged.

but when rotating speed increase, the torque also increase.

anyone can help?

• DrAmine
Ansys Employee

Your torque is constant from the plot. Can you please add some more information here? If there is a linear momentum then the torque will change even at constant angular velocity.

• motoyama
Subscriber

Hi Amine,

below is example of angular velocity and torque and Cp values

what do you want else?

• Rob
Ansys Employee

OK, why should torque be the same for different speeds? Ie, what is the definition?

• motoyama
Subscriber

Hi , rwoolhou

the torque value means half of the moment that i calculate

well, I think torque is not same as for different speeds.

from the tip speed ratio, there should be a Cp peak.

• motoyama
Subscriber

• Rob
Ansys Employee

I'm not sure I understand.  If you expect the torque to change with speed, what is the problem?

• motoyama
Subscriber

the problem is that torque increase and decrease as the rotational speed increase.

so Cp=torque x omega should have peak.

but this data shows torque only increases but not decrease.

• DrAmine
Ansys Employee

From the data you are mentioning I do only detect  single trend: torque is increasing as the angular velocity is increasing (due to linear mometum). So now: What is the problem?

• motoyama
Subscriber

Hi Amine

I searched the similar examples

https://www.cfd-online.com/Forums/cfx/160097-problem-torque-calculation.html

• Rob
Ansys Employee

That's not the problem, you need to define & explain why you think your answer is wrong. As you've read through the whole of that thread, have you also found the same problem with a finer & much finer mesh?