One of the taps in my bathroom at home issues water in laminar flow – without any turbulence. Sometimes the flow from the tap to the bucket looks like it’s frozen: there are no disturbances on the water’s surface to indicate that it is flowing through the air; the fact of the flow becomes evident only when it strikes the water already in the bucket.
If the water in the bucket is otherwise still, i.e. undisturbed by any other jerking motion, the flow from the water seems to create a small depression when it strikes the surface, like a ball might create a depression when it lands on suspended fabric. But when I took a closer look, it was less a depression localised to the surface and more the origin of a vortex plunging into the water, like an underwater tornado!
When I closed this magic tap and opened the one next to it, it gushed a turbulent stream of water into the bucket. There were no vortices, or none that I could see. I remember learning in engineering college that turbulent flow is characterised by the production of many vortices that all interact with each other in a chaotic way, creating a drag force that impedes the fluid’s smooth flow.
Where there is a vortex, there is or will be turbulence. In this case, the laminar flow from the tap could be transitioning to a turbulent state as it flows into the still water, until at the bottom of the vortex the flow dissipates completely. Such a lovely sight.
