The Interior Tunnels

Interior tunnels connect two spiral arms of the same spiral vortex without connecting to any other vortex externally. The connection happens at the high end of the spiral that is located at the inner end of the vortex and so far this only applies to vortices above the central balance point. Only two of these types of vortices are known at this point, which is the gyroduct, which forms at the inner end of the revolute, and the ultraduct, which forms at the inner end of a scroll ring.

Interior tunnels are hollow vortices that are completely enclosed. There are no openings in its outer shell. From the few observations of an interior tunnel we might suspect that such a tunnel can not exist without the two spiral arms. I have only seen interior tunnels within spirals, not as standalone vortices. While the vortex is hollow, I do suspect that some other medium, or a different density of medium is contained within the vortex.

I am not sure if there are other type of vortices that precede these two vortices below the eighth dimension level. I expect there to be no interior tunnels of a lower dimensionality than the gyroduct, but it could very well be that some other class of vortex is what precedes the gyroduct in the morph sequence. If so, then those vortices should connect to the outer end of the spirals, not the inner end, because below the central balance point this characteristic is mirrored into its opposite.

Gyroduct

The vortex that connects two revolute spiral arms at their inner ends, making a hollow 4.25D tube, is called the gyroduct. The whirlpit has a periphery, we know this because it is a visible vortex. Because the whirlpit connects to the inner end of two revolutes, it is also likely that it has no core. The gyroduct is the high dimensional equivalent of the whirlpit. One vortex lies 1,5 dimensions above the central balance point, the other lies 1,5 dimensions below the central balance point. The gyroduct is a rotational vortex.

The image below shows how the gyroduct looks like deep within a revolute. The gyroduct lies at the same position where a belt would start. The gyroduct is nothing more than a circular tube. It is unknown how many individual movements it has or how the trajectories of those movements look like.

(There is a mistake I made in this image. The cross-section of the gyroduct is supposed to be circular, not egg shaped. Only the outer windings of a revolute are non-circular and get progressively rounder as they spiral to the center. But it is quite difficult to make a complete correct 3D model.)

From the outside, a gyroduct looks somewhat similar to a scroll ring, which is not hollow but spirals inward. But despite that both vortices are donut shaped, it is not that hard to tell them both apart. First way to tell them apart is that a scroll ring is thinner than a gyroduct, but only when the scroll ring is unmorphed. A descended scroll ring can look just as thick as gyroduct. So this characteristic alone is not always enough to tell them both apart. A better way to tell them both apart is the presence of a revolute around the gyroduct. If you see a vortex ring deep within a revolute then that vortex is gyroduct. When there is no revolute around the vortex ring then that vortex ring is a scroll ring (or an ascended revolute, which is almost the same).

(A scroll ring can also appear deep within a revolute, connected by a belt, which is something that is predicted by the transformation sequence. But unfortunately, that hasn't been observed yet).

Gyroducts are found only within some revolutes. The reason as to why it forms in some revolutes and not all is not clear to me. An example of a gyroduct is the bright ring deep within a mushroom cloud (mesocyclic). Gyroducts are also observed in outer space. There, the revolute can not be observed, you can only see the gyroduct. This is logical because the revolute is the state of equilibrium for the outer space medium, this means that the outer space medium already behaves like one big revolute, and a revolute itself can not be observed in that medium.
 

The Bright Ring Deep Within a Mushroom Cloud

In some mushroom clouds you can spot a bright ring in the center of the vortex. This ring is often mistaken for one of the inner windings of the revolute. But it is not one of the inner windings. This ring is much brighter then any of the preceding windings of the revolute. There's a clear distinction between the density of this vortex and the vortex around it. In the left image you can see that the ring is made of what looks like bright hot plasma. The ring is hotter then the rest of the mushroom cloud. The reason that this ring is hotter because for at least one reason it must be higher dimensional than the rest of the mushroom head. Yet it is probably not the dimension level that makes it higher dimensional. Perhaps the vortex is higher dimensional because it merges two vortices together, thereby combining their number of meridians.

In the image on the right you can see a ring that is blown by a volcano. Around the ring you can see a revolute. If we would not have paid attention and we had not seen the revolute then we would have believed that it was a scroll ring, but it is in fact a gyroduct. Here too the ring is very bright.

Core of a vortex ring. The ring is produced by diffraction of a pressure pulse out of a tube in air. The waves have subsided, leaving the vortex ring moving away from the mouth of the tube. The dark portions of the core are visible in this spark shadowgraph because of the naturally occurring reduced density in the rotational flow. In addition, the tube was precooled to aid in the visualization of the outer portions of the ring. Only the upper half was photographed, and then reflected in the axis to give the effect of a complete ring. Photograph by Bradford Sturtevant [text and image from 'An Album of Fluid Motion' by Milton van Dyke. Image was edited with text and lines].

The image above shows a gyroduct within a revolute. Here you can clearly see that this vortex is hollow. There's a thin line at the center of the gyroduct which could be a ultraduct.

Ultraduct

The vortex that connects two scroll ring spiral arms at their inner ends, making a hollow 5.25D tube within the spiral, is called the ultraduct. The shape of this vortex is that of a hollow hoola hoop, a very thin torus. The ultraduct is a rotational vortex.

The logic as to why this vortex is expected to exist is quite clear. There is one such internal tunnel vortex at the inner end of the revolute, so one would expect to find a similar class of vortex at the inner end of the scroll ring. We know more or less how the gyroduct forms and what its shape is, so we can predict the shape of the ultraduct, based on shaped of the scroll ring and the location of the inner end.
 

Screenshot from video by Dustin Kleckner & William T. M. Irvine (2013). Line and text was added.

The video above shows one such ultraduct (in the first part of the video). It is an ultraduct at the inner end of a scroll ring. The fluid that is ejected forms a highmorph revolute which will eventually morph into a lowmorph scroll ring. If the ejected fluid had formed an unmorphed revolute then the vortex ring within that revolute would probably form a gyroduct, which is a much thicker ring. Because of the proportions of this ultra thin ring it is however most likely that we are looking at an ultraduct. Scroll rings and tubular rings can not reach such a thin radius by morphing before its shape collapses. Also, as you can see in the video, the vortex around the thin bright ring is morphed into a higher state that that of a full revolute, it looks almost like a scroll ring.

The ring in the video is very high dimensional, it contains many meridians (individual movement), for this reason it is possible to create a similar type of vortex with a knot, as the video shows. One would not be able to create a knot in a vortex that is low dimensional.