About the panel method of VAPAERO

[muku]

Hello,

I have a question about the VSPAERO panel method, so I created a talk room.

Does the panel method here output the calculation result considering wave drag?

muku

[Rob McDonald]

The VSPAERO panel method only works subsonically.  Consequently, it does not capture wave drag.

You can also run VSPAERO in a thin-surface mode supersonically.  This mode will not capture wave drag due to volume.  It models linearized supersonic flow, so you will need to dig into that a bit to fully understand what is captured and what is not.

OpenVSP also includes a wave drag module specifically for estimating wave drag due to volume.  This uses the standard linearized theory based on the area rule.  This calculation is separate from VSPAERO.

Rob

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[muku]

Dear Rob McDonald

Thank you for answering!

I will contact you if you any new questions.

muku

2021年1月15日金曜日 3:02:15 UTC+9 Rob McDonald:

[muku]

Dear Rob McDonald .

When calculated by the panel method, Cp is displayed in Launch Viewer.

Is it possible to check Cp numerically here?

For example,

I want to check the change of Cp in the red line part of the photo with a graph.

muku

2021年1月17日日曜日 20:59:10 UTC+9 muku:

[Rob McDonald]

You want to check out the 'CP Slicer' option on the 'Advanced' tab of the VSPAERO GUI.  It should allow you to place a cut like you want and then extract Cp data for that cut.  The slice data will display in the graphical Results Manager.

One thing to note.  The way VSPAERO works, the Cp distributions are a final post-processing step.  They are not actually used for calculating aerodynamic loads.

There are some approximations involved in generating the surface Cp (there are approximations with everything).  So, while a good Cp distribution is certainly indicative of a good solution, a less good Cp distribution is not necessarily indicative of a bad solution.  The solution and loads can be great -- and the Cp distribution might not be a great match.  That is OK.

Rob

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[mike]

Hello,

I have a question about the drag coefficient of VSPAERO panel method.
I recognize that the drag coefficient is composed of parasite drag and induced drag.
Does VSPAERO consider parasite drag?

Muku

2021年1月29日金曜日 2:14:01 UTC+9 Rob McDonald:

[Rob McDonald]

VSPAERO has a very simple parasite drag model.

CDi is the inviscid drag calculated by summing forces on vortex elements.

CDt is the inviscid drag calculated by a trailing edge technique.

CDo is the parasite drag

CDtot = CDi + CDo

CDtott = CDt + CDo

Rob

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[Reji Rejish]

Hi Rob, 

If I understood correctly, the trailing edge technique that you mentioned here is the trefftz plane integration. Am I correct?

Best regards, 

Rejish

[Brandon Litherland]

That's correct.  For VLM mode, you'll likely see CDi and CDt nearly overlap except for more complex cases.  Panel mode will tend to show more drag at higher alpha for CDi than CDt when spanwise resolution is lower or the tip gradient isn't being captured well.  Increase Num U and/or tighten the tip clustering to bring CDi and CDt into alignment.

[Reji Rejish]

Thank you very much for your support.

[Rob McDonald]

As Brandon says -- yes.

I usually refer to it as Trefftz-like as there are some differences in the formulation and approach, but it uses those core ideas.  I am not fully versed on those differences.

For example, my understanding is that the Trefftz plane formulation only works for steady flow -- the extension that has been put together for VSPAERO also works for unsteady flow

Rob