Vort-X tunnel fins: is there really a vortex?

According to my visualisation of half pipe tunnel fin flow, there's a slight but significant twisting of the flow as it passes through the enclosed pipe. I've been talking about this for many years, and some people have been sceptical about the existence of this vortex.

Yesterday Hans from the finfoil project posted images from his computer flow modelling of a half pipe tunnel fin, proving that the vortex is real.

The pictures show a tunnel fin with an angle of water flow attack at ten degrees:

vort-x tunnel fin for surfboard flow modellling image 1

Aside from the drag reducing benefit which the tunnel gives ny absorbing and managing the chaotic turbulence which leaves the trailing edge of the leading, planar fin (If it doesn't have leading edge vortex generators) the vortex induced by the half pipe tunnel has another advantage.
Normal flow inside a pipe produces drag inducing spanwise vortices. In the case of the half pipe tunnelhowever, the twisting motion induces beneficial lengthwise vortices instead. A full cylinder won't do this, it's the asymmetry of the half pipe which causes it.

The dreamliner aircraft uses a tunnel with trailing edge undulations to improve flow mixing and reduce drag.

Why use a tunnel fin?

A tunnel fin overview.