# What happens when the surface ends at the laminar zone of the boundary layer?

When a body travels through any fluid(like aircrafts and cars), due to viscosity of the fluid a boundary layer is formed around the surface of the body which separates the velocity of the fluid inside the boundary layer(near the surface of object) to velocity of the fluid.The boundary layer consists of three zones laminar, transient and turbulent zones respectively.

Is it compulsory for all the three zones to exist in a boundary layer? If we consider a small smooth surface, is it possible that the surface ends at the laminar zone of the boundary layer and there is no turbulent zone in boundary layer over the surface? And if it is possible will there be a low pressure zone at the end of the surface or something?

• Useful search term : "Reynolds number". Commented Nov 2, 2016 at 11:00

It is certainly possible to achieve this in certain circumstances for example http://www.aviation-history.com/theory/lam-flow.htm

Typically it is a lot easier to claanly accelerate a flow arround the leading edge of a surface than to keep it attached as the flow converges again. So the best chance of achieveing this is a long tapering teardrop shape as in sprint cycling helmets and some solar powerd endurance vehicles.

However in practice achieving completely laminar flow tends to compromise practical design to the extent that it is not useful and most practical aerodynamics is more about managing turbulence and vortex generation rather than attempting to eliminate it entirely.

For example in F1 cars a lot of engineering effort goes into making vortices do a useful job (particularly) in separating the turbulent wash from the tyres from the laminar flow under the floor/diffuser)

Is it compulsory for all the three zones to exist in a boundary layer?

in practice, yes.

If we consider a small smooth surface, is it possible that the surface ends at the laminar zone of the boundary layer and there is no turbulent zone in boundary layer over the surface?

IF you have a sufficiently smooth surface, and sufficiently slow velocity, the NSE simplify (I use the term loosely) into a PDE that can be solved analytically. (stokes flow around a cylinder or sphere, for example)

The fact that they can be solved analytically indicate that the flow is not turbulent! (again, this is theoretical)

And if it is possible will there be a low pressure zone at the end of the surface or something?

I'd have to crack open my fluid mechanics books before I can give a definite answer