Parasite Drag Tools

[Gordon Yuhim Lai]

Hi,

I have been recently exploring the parasite drag tools that comes with OpenVSP 3.13.3. Yet when I clicked "Calculate CD0" after importing the sketched components to the table, the table disappeared and all my components became " No show" in the sketch pad, without giving a result at the bottom-right corner of the Parasite Drag's UI. I note that the table was blank (except laminar % and Q, which are the only edit-able items) after I import the components to the tools, is this what caused the problem?

By the way, is there any tutorials or standard procedures for using this tool?

Attached is what it looks when I selected the components to be calculated with the tool.

Thanks.

Gordon

[Rob McDonald]

The first thing the parasite drag calculator does is to run CompGeom.  This may include no-showing all the components.  It should show the resulting Mesh though.  If the mesh didn't appear, I suspect it was a problem with CompGeom -- are all your components individually water tight?

If you run CompGeom on its own, it may give you some clues to the problem.

Rob

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[Gordon Yuhim Lai]

Thanks for the help Rob.

I have made sure all my components are individually water-tight, as there are no indication of open meshes in CompGeom. However, I found that if I run Parasite Drag tools with "All" set instead of "Shown" set, the tool works fine. So I doubt if there is a small bug in the set selection.

By the way, is there anyway to know whether the CD0 from the result is reasonable? (i.e. no meshing problems)

Thank you very much again.

Gordon

Rob McDonald於 2017年10月23日星期一 UTC+8下午10時31分15秒寫道：

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[Rob McDonald]

Ahh, I didn't catch that you were using 'Shown'.  I'll check to see if I can find a bug related to that.

In the meantime, I suggest you either create a 'OML' set to use for Parasite Drag or, stick to using 'All'.

The meshing is pretty robust -- it either works or it doesn't.  If components come back with zero wetted area, then you want to check them out.  If it comes back with a reasonable area, you're good to go.

Rob

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[Gordon Yuhim Lai]

Rob,

Thanks for the help. Recently I found that some of my components got zero wet area (especially pod geom and vertical wing geom), resulting in zero CD0, What could cause the problem? On the other hand, does the tool handle components individually? Can it handle components which are partially overlapping with each other as a whole just like the vspaero?

Many thanks,

Gordon

Rob McDonald於 2017年10月24日星期二 UTC+8下午12時10分01秒寫道：

[Rob McDonald]

Try running CompGeom stand-alone on the same Set.

It will likely report that some open geoms were dropped.

Not sure how this would happen with a Pod, but perhaps it had trouble for some reason -- you could try making a small perturbation to your geometry.

Yes, the CompGeom process calculates the wetted area and uses that for the Parasite Drag buildup.

Rob

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