Air Strippers - what if the barrel itself was a cone??

[Turnup]

There's a big difference between a shock wave and flow. One is a pressure wave propagating through the medium, the other is the medium moving.

Yes there is, and Schlieren photography can reveal both. I once took a Schlieren photograph of the turbulent heated air rising off my outstretched hand.

EDIT: more precisely it reveals density differences, from which flow can be deduced.