Bug found when using twist

[Hussein Nasr]

Hello VSP team,

 

I am designing a flying wing and I notice that when I have a twist that ranges from 5 degrees root to -3 degrees tip, the cl and cl*c/cref curves have spikes. I noticed that the spike always happen right at the section where the AOA across the span goes from positive to negative. If I change the twist or move the section where the AOA goes from positive to negative across the span there is always a large spike at that section. If I select a high AOA so no section across the span switches AOA sign then the spike will happen at the tip.  

 

I thought it might be a numerical error problem as things get close to 0 deg AOA. So I tried rotating the wing 90 degrees around the y axis and adjusting the AOA to -90. This caused the spike to disappear in version 3.1.2.1. The curve was very smooth.  When I updated to 3.1.3.3 the spike came back when I rotated to 90 degrees w/ -90 AOA and the spike was the same un-rotated. So no matter how i rotated my wing + AOA the results where the same. 

 

I was wondering what I can do to get around this anomaly or if Aerovsp even supports large twist distribution. 

The files I have attached is an example of the spike I mentioned. 

Thank you

[Rob McDonald]

That is an interesting observation.

Can you put together a simple example file that recreates this problem
with the latest version?

Rob

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[corp...@gmail.com]

Hi Rob and Hussein,

I tried to replicate the problem in version 3.13.3. win32.

Flying wing with only one section, root incidence of 5° and tip twisted -2°. Tip cluster is 0.15. Airfoil of root and tip are the same (randomly chosen Naca4415).

VLM analysis with a.o.a. range -6°<alfa<8°

The pictures show the results, where the spike is present at the tip but , in this test, doesn’t appear in any intermediate section in a.o.a. range.

 

Corrado