Question regarding the design of a HAWT blade

Quote from Bob on 30. November 2022, 03:39

I have 6 graphs displayed.

But the alpha and Cl/Cd graphs are not displayed.

What should I do?

 

Bob

Quote from David on 30. November 2022, 08:33

Hi Bob,

check out the documentation: https://docs.qblade.org/src/user/guigraph/guigraph.html#graph-functionality

Best,

David

Quote from Bob on 1. December 2022, 07:13

Hi David,
After importing an Airfoil from Clipboard, I used Airfoil module analysis, but, It didn’t work.
And I got
– Polar should have at least 10 points (currently: 0)
– At least 5 data points in the range 0 < alpha < 20 needed (currently: 0)
” in the Polar extrapolation section.
Sometimes the message doesn’t shows depending on the Airfoils which I import.
Could you manage that?

I appreciate your kindness.

Bob,

Quote from David on 1. December 2022, 11:49

Hello,

are you saying that the XFoil analysis is not working properly for an airfoil? Could you explain the issue more precisely and maybe share a screenshot of the issue?

At least 5 data points in the range 0 < alpha < 20 needed (currently: 0)
” in the Polar extrapolation section.

The above error message is shown when you try to extrapolate a polar that does not have enough data or is empty – so this is normal if XFoil fails.

BR,

David

Quote from Bob on 5. December 2022, 09:10

Hello,

I have designed a forward wing, but the efficiency exceeds the Betz limit.
Why is this?
If you don’t mind, please advise.

Thank you for all your replies.

 

Bob

Quote from David on 5. December 2022, 11:21

Hi,

your simulation is not converged yet. Opposed to a imple steady BEM both the unsteady BEM and the Lifting Line take into account the unsteady wake dynamics (or wake development). This means that it takes a couple of rotor rotations until the CP value has reached a steady state value. In your case you need to either simulate for a longer time or set the “Convergence Acceleration Time” to some time larger than zero so that the rotor reaches its steady state faster.

Best,

David

Quote from Bob on 5. December 2022, 13:30

I appreciate your reply.

I have tried setting the “Convergence Acceleration Time” to 10, 100, and 1000, and the efficiency is 0.56, which is still greater than Betz’s limit.

Bob,

Quote from David on 5. December 2022, 17:32

Hey Bob,

the Betz limit is around ~59%, so it should be ok…

Best,

David

Quote from Bob on 15. December 2022, 08:12

Hello David,

I have two questions.

The first is that the analysis result of Cp of “rz_0.3_6” in the attached file “final” is 1.17, which exceeds the Betz limit. Why is this? I think the values are converging.

Second, what is the difference between the Cp in the BEM and the Cp in the simulation with the icon of the rotating windmill and vortex? Sorry I have not read the manual properly.

Bob