# Pitching moment and Yaw moment coefficient

Dear Bonnie.Jonkman,

I want to ask you about difference of experimental data and simulation results.
The experiment and input of FAST are the same.

Input: 2-blade downwind, hub height: 1.6m, rotor radius: 0.8m, mainstream velocity: 8m/s
parameters of bade and tower of FAST are used from other experiment.

The cyclic pitch control was used in this experiment.
For pitching moment: phase of pitch angle = 45 deg, both results are the same.
phase of pitch angle = 0 deg, there is difference.
Why is there difference?
Simimlarly with Yaw moment?

Thank you very much for your help.

Le Quang Sang.
New Microsoft Word Document.docx (1010 KB)

Dear Le Quang Sang,

I’m sorry, but I don’t really understand what you are showing or asking. A few questions:

• In your plots, are some of the results from FAST and some of the results from experimental data…if so, which?
• What is meant by phase of the pitch angle?
• Are you plotting the amplitude of the tower-top pitch and yaw moments as a result of cyclic pitch on the y-axis?

Best regards,

Dear Bonnie.Jonkman,

I’m so sorry, I told unclearly. Can you explain the difference of simulated results and experimental data?
Parameters of bade and tower of FAST are used from other experiment.

1- I used cyclic pitch control to decrease load of WT. Pitch angle is defined as in the attached file
2- Pitch moment and yaw moment are considered on the rotor surface.
pitch moment on the x-axis, yaw moment on the z-axis.

Le Quang Sang.
New Microsoft Word Document.docx (1.01 MB)

Dear Le Quang Sang,

A couple more questions:

• Does the y-axis on the plots show the resulting amplitude of the cyclic moment?
• Does the simulation or experiment have a shaft tilt or shear, or is the flow uniform are perpendicular to the rotor?

Best regards,

Dear Bonnie.Jonkman,

1. the y-axis on the plots are the resulting amplitude of the cyclic moment
2. the conditions of experiment and simulation are the flow uniform and perpendicular to the rotor.

what is the difference between experimental data and simulation results?

Le Quang Sang.

Dear Le Quang Sang,

OK, I finally understand what you doing.

To me, the FAST results make sense because at 45-deg phase angle for the cyclic pitch angle, I would expect identical magnitudes of the cyclic pitch and yaw moments, which is what FAST is showing. However, the experimental data does not show this consistency.

Best regards,

Dear Bonnie.Jonkman,

I’m so sorry, because I didn’t understand clearly.
Can you explain clearly for me?
What is the reason caused in that phenomenon?

For the pitch moment:
At phase of pitch angle is 45 deg, there is the same results both the experiment and simulation.
At phase of pitch angle is 0 deg, there is large difference.

For the yaw moment:
At phase of pitch angle is 0 deg, there is slight difference of the experiment and simulation.
At phase of pitch angle is 45 deg, there is large difference of the experiment and simulation.

Note: in the two figures, the pitch angle is negative, the difference is larger than positive pitch angle.

Best regards.
Le Quang Sang.

Dear Sang,

I don’t really know why the experimental results are different from FAST. I was simply pointing out the inconsistency in the experimental results at 45-deg phase angle, where I would expect the magnitude of the the pitch and yaw moment amplitudes to be identical, which is what FAST is showing, but is not what the experimental data is showing.

I would review the experimental set-up to understand why it is showing this inconsistency at 45-deg phase angle.

Best regards,

Dear Bonnie.Jonkman,

Thank you very much for your help.

My experiment carried out in the wind tunnel.
It is attached.
Please see it and suggest for me.

Best regards.
Le Quang Sang.
Experimental condition.docx (39.9 KB)

Dear Sang,

I’m sorry, but I can’t really comment as to why your experimental data is showing an inconsistency at 45-deg phase angle.

Best regards,

Dear Bonnie.Jonkman,

Thank you very much for your email.
I also find the reason.

If you have idea, please talk to me.

Best regards,
Le Quang Sang.