B What is my yogurt doing?

[ROGER WALL]

Hello, I don't know anything about fluid dynamics and hope someone can tell me what it is I saw the other day. I work in yoghurt factory and had to throw out a whole vat full of product (the culture died). So i pumped the product thru a say 70mm hose and poured it into a waste bin (which was being sucked out from the bottom as I filled it up - don;t know if this has something to do with it - don't think so).

Anyway as i stood mesmerised (took 20min to dispose of all the yoghurt) i noticed that a void existed around the round stream of yogurt coming out of the hose as it entered the pool of yoghurt in the container. Being a white liquid (as oppes to looking a water) it was easy to see this 0.5mm - 1mm void around the stream of yoghurt as it formed a dark shadow.

Also the yohurt in the pool was sucked down the 'outside' of the void - proabaly not surprising - like water going down a drain hole.
SO this void - does it have a name (fancy name not just surface tension, etc). Is this phenominar used for anything? Thanks, ROger.

 

[Baluncore]

SO this void - does it have a name (fancy name not just surface tension, etc).

The stream of fluid entering the surface creates a shear zone below the surface, that is dragging fluid downwards outside the entering stream. That results in the gap forming in the viscous fluid at the surface, outside the entering fluid.

A failed yoghurt may be a non-Newtonian fluid.
There is no eponym that I know of for the described effect.