Parasite drag calculation of cylinder

[Tasos Seitanidis]

Hello and happy new year,

I am trying to validate OpenVSP's parasite drag results by using a circular symmetric cylinder stemming from the StackGeom. As I understand it, the tool always assumes that the geometry is facing the flow direction (which in my case should have been perpendicular to the cylinder) and for this reason I can't get the correct results. My question is how do I use the tool correctly in my case? Is the geometry selection wrong? The answer could be simple I guess, but I am really new here.

Thanks in advance,

Tasos

[Rob McDonald]

Not only does OpenVSP assume the flow is generally aligned with the original orientation of the StackGeom -- the form factor equations are based on non-separated flow.  So, even if you made something that oriented properly looked cylinder like, it would still not have the right drag.

Rob

[Tasos Seitanidis]

Thank you for the answer. Is it possible to do this another way or should I use a different tool?

[Rob McDonald]

You should use a handbook method such as Hoerner's Fluid Dynamic Drag to estimate the drag on the cylinder.

If it is a part of an aircraft model in OpenVSP, you should then add it to the rest of the buildup as an excressence.

Rob

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[Rob McDonald]

In this case, the parasite drag tool is treating the cross section as an attached airfoil with t/c=1.0 -- there is little reason to think this corresponds well to a cylinder.

Rob

On Tue, Jan 2, 2024 at 11:44 AM Tasos Seitanidis <tasos...@gmail.com> wrote:

For anyone interested I think I solved the issue by using a wing and circular coordinates in the airfoil file. This way the parasite drag tool gave me correct results for the cylindrical geometry. Thank you again for your answers.

To view this discussion on the web visit https://groups.google.com/d/msgid/openvsp/c9cef593-f552-42bd-b9f5-e16795d44c91n%40googlegroups.com.