Question

Which type of flow (laminar or turbulent) is preferred when there is a high tendency for the flow to separate and why?

Answer 1

Hey .
Here is your answer.

A laminar flow is certainly "nicer" than a turbulent one, but that is not always what you want when you want to reduce drag. In particular, there's no obvious reason why dragging fluid around (via a laminar wake) is going to be better than casting it off, as shed vortices go.

In particular, keeping the main part of the vortex around will mean that you've got a continuously-reinforced low-pressure system behind you. Shedding it means that it can go on its merry way, and stop sucking you backwards. You can therefore think of it as trading a constant drag for a sawtooth wave of sorts.

The higher the fluid velocity relative to the surface, the lower the pressure. In the turbulent case the higher relative velocity leads to lower pressures near the surface such that pressure from the surrounding fluid further away from the surface (the same in each case) forces the streamlines towards the surface for a longer distance compared to the laminar case.

Thanks.