With refference to the lifting line model, do we consider trailing votex or vortex sheet to be inside the flow field ? because the vortex core is rotational and we violate one of the flow field requirements of potential flow ?

If the answer is no, for far field integrals do we consider a control volume with a paper like cavity from trefftz plane to the wing excluding the wake ?

Thanks and appreciate any feedback


1 Answer 1


No, the starting vortex is not part of the flow of interest. This is because, as you mentioned, the flow is treated as potential but a vortex is rotational (and its very formation requires viscosity, so that's another strike against including it in these idealized models).

So what happens is you cut the domain apart into two pieces. If I may reuse my stunningly beautiful illustration from another answer, you end up with a domain like:

enter image description here

where you ignore the right side of the cut line and consider only the left side of the cut line. Global vorticity is conserved and Lord Kelvin rests easy because we "attach" a fixed vorticity to the wing itself. Or to the lifting line or the small panels or whatever approximate method you are using.

  • $\begingroup$ Hi, thanks for the reply. I was actually asking about trailing vorteces not the starting $\endgroup$
    – Jujubs
    Feb 9, 2017 at 6:21

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