Number of Panels chord wise and span wise

[ey1...@my.bristol.ac.uk]

Hi,

I'm fairly new to VSP and was wondering whether you could tell me how I can change or specify the number of panels I would like on a wing chord-wise and span-wise? Is there an option for this and if so can you please tell me where I can find this?

Thanks

Regards

Edward

[Rob McDonald]

The chordwise direction is set on the 'Gen' tab under 'Num W'.

The spanwise direction is set on a per-section basis on the Sect tab
under 'Num U'.

The spacing clustering can be controlled. Chordwise at the bottom of
the 'Plan' tab, spanwise per-section right next to the Num_U slider.

Rob

> --
> You received this message because you are subscribed to the Google Groups
> "OpenVSP" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to openvsp+u...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.

[ey1...@my.bristol.ac.uk]

Dear Rob.

Thank you for your reply. Unfortunately I am having a few issues with what you told me. I have tried to change the number of panels chord wise to a value of 2 but the 'Num W' box keeps displaying a value of 5 for some reason and would not lower to a value lower than this despite the help box saying that the minimum value of 'Num W' is 2

In addition, if I am to create a simple rectangular wing WITH symmetry in the x-z plane, and want to specify 2 panels chord wise and a total of 10 panels across the span, am I right in saying that I would need to have a value of 3 in the 'Num W' box and a value of 6 in the 'Num U' box? Could you please correct me if I am wrong please

Regards

Edward

[Rob McDonald]

Edward,

Why are you trying to achieve such a coarse resolution?

VSP has been designed to enforce some minimum resolution in this case.
The minimum value for NumW of 2 is misleading. In fact, it does some
behind-the-scenes conversion to limit valid values to (n*4+1) where n
is restricted to integer values of at least 2. That is why it will
only take values of 5, 9, 13, 17, etc.

This parameter controls the number of points to evaluate -- set to 5,
it forces a trailing edge, lower-surface middle, leading edge,
upper-surface middle, and back to the trailing edge. When you set it
to 9, you add an additional point in the middle of each of those
locations...

I hope this makes sense,

Rob

[ey1...@my.bristol.ac.uk]

Dear Rob,

Thank you for the reply. So if I was to change the rectangular wing to have 5 panels chord wise and 10 panels chord wise, am I right in saying that I would put 'Num W' as 5 and 'Num U' as 6 if I enable symmetry in the x-z plane then? Sorry its just that I am a bit confused with the span wise paneling concept now

Also from your response regarding Num W, you said that: 'This parameter controls the number of points to evaluate' and so just to confirm that the number of points evaluated also represents the number of panels (in the chord wise sense)? So a value of 5 for Num W represents 5 panels?

Regards

Edward

On Monday, August 1, 2016 at 10:26:26 PM UTC+1, ey1...@my.bristol.ac.uk wrote:

[Rob McDonald]

Edward,

I think you're getting yourself a bit over-confused.

Look at what you have on screen. Perhaps change the drawing style to
'Hidden'. Count the number of panels and observe what you get.

What are you actually trying to do? Are you not able to achieve it right now?

Rob

[ey1...@my.bristol.ac.uk]

Dear Rob,

Yes so I've set the view mode to Hidden but when I select the Top down view, with Num W set to 5 and Num U set to 6, I see 10 panels across the wing span but chord wise I see 2 panels. Is this what I should be expecting?

Regards

Edward

On Monday, August 1, 2016 at 10:26:26 PM UTC+1, ey1...@my.bristol.ac.uk wrote:

[ey1...@my.bristol.ac.uk]

Sorry I forgot to mention I am currently investigating the effect on accuracy of Cl and Cdi as I increase the number of panels chord wise and span wise for a simple rectangular wing

On Monday, August 1, 2016 at 10:26:26 PM UTC+1, ey1...@my.bristol.ac.uk wrote:

[Rob McDonald]

I don't know what you are expecting.

That is what the code does. That is what I expect it to do.

If you then rotate and look at the bottom of the wing, you will then
see two more panels. So, does it have two chordwise, or four?

Each panel has a start and end point. The first point (at the
trailing edge) is actually repeated. So, if you count endpoints, you
end up at five....

In truth, there are more than just the two duplicate points at the TE
-- We represent it as if those are the only two, but if you trim or
thicken the trailing edge (Modify tab), you'll see that there are in
fact more! And if you trim or thicken the leading edge, you'll find
yet more points.

'Normally' these are invisible on screen. If you don't Modify the
airfoils, they don't matter. However, it depends on what you are
going to _do_ with the wing. Are you going to output it in some
format for some analysis? If so, then you might care about those
repeated points. Hence all the questions about what you are actually
trying to do...

If you are using the thin-surface VSPAERO method, it generates a
'DegenGeom' based on the wireframe you see on screen. In DegenGeom,
the wing is smashed into a thin surface -- where the top and bottom
chordwise panels are smashed into mean-surface panels -- and you end
up with about half as many.

If you want to see what VSPAERO is doing, go into its viewer and
choose the option to view the mesh. That will probably answer all
your questions.

Rob