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Sonic tubes

Posted: Sun Jun 04, 2017 9:42 am
by Robert Biegler
The designer of the Rave V foiling trimaran says that sonic tubes at the junction of V-foils reduce cavitation. See from 12:30. Does anyone know how these work? When I search for "sonic lifting tube," I only get sites associated with the Rave V, asserting the benefits without explanation of how these things work.

Re: Sonic tubes

Posted: Tue Dec 05, 2017 8:54 pm
by John Perry
Having just watched the part of the video that you refer to I have to say that this sounds suspiciously like an attempt to impress the viewer with scientific sounding waffle! If the presenter believes that the 'sonic tube' design provides a performance benefit then why does he not present data to support this, or at least offer his reasoning as to why he thinks there may be a benefit?

He talks about vortices being generated at the junction between the two legs of the 'Vee'. If there is no side loading on the hydrofoil assembly, i.e. only lifting force, then the apex of the 'Vee' is right on the plane of symetry and surely there is no flow perpendicular to such a plane of symetry, so I would have thought no vortex generated from any point on that plane. Adding a side loading, as occurs due to lee way on a sailing craft breaks the symetry and would be expected to produce a vortex, although since the geometry of the whole craft sugests that such side loading is fairly small compared to the weight of the craft this would a relatively weak vortex. I cannot guess whether a tube located at the apex of the Vee would reduce the effect of such a vortex but it will certainly increase the total wetted area and hence skin friction.

I think it has been sugested that it is beneficial to include a streamlined body of rotation - a 'torpedo' shape - at the junction between two foils and indeed I have an idea that this has been incorporated in some successful designs of 'Tee' foil rudders. I dont know what evidence there is to support this idea, I would be interested if anyone can shed light on this. I can see that a solid 'torpedo' at the bottom of the junction might offer some structural benefit, or possibly simplify construction if the Vee is constructed as two separate legs that are then joined.

I would think that Computational Fluid Dynamics analysis (CFD) could provide understanding of the flow in this situation and could enable assessment of any benefit due to either a tube or a solid shape at the apex of the Vee. Indeed I think there is huge application for CFD in better understanding many aspects of sailing boat design.

Sonic tubes? what has this to do with sound?