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When a body travels through any fluid, 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?

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    $\begingroup$ Likely related: On The Critical Reynolds Number For Transition From Laminar To Turbulent Flow (here). $\endgroup$
    – mins
    Nov 1, 2016 at 12:06

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Then you get a fully laminar boundary layer without transition. This can happen at very low Reynolds numbers, especially if no steep positive pressure gradients are encountered.

A steep pressure rise can lead to separation, and if the boundary layer does not change to a turbulent one, this separation can be final, with no re-attachment of the boundary layer. Then the attached flow ends before the body ends, but still the boundary layer is fully laminar.

It is not compulsory for transition to happen. If the flow is stable (either due to a negative, stabilising pressure gradient or due to very low Reynolds numbers), the boundary layer will stay laminar for its full length.

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