I'd
previously mentioned Open VDB and
what it portends. Now a SIGGRAPH preview reel pointed me to:
My current understanding of Clebsch Maps is that they represent the normals to the direction of flow. One point of interest, the Delta Wing Data Set, at 1:42, suggests that vortexes are not open-ended but are loops closed at the diffuse end (shown in the thumbnail).
Se also Fluid Processing at 0:56.