Resolving the Low Reynolds Number Paradox: Wake Formation

[Cosmossos]

The wake is made because the inertia forces in the system ,right? So if i have low Reynolds number the inertia forces are negligible and the flow doesn't separate ,right?
So In every low Reynolds number the flow doesn't separate (no wake) but low Reynolds number also indicate a viscous flow which in it there is a wake.
So we get that for low Reynolds numbers we can get a wake or not which it isn't possible.

please help me resolve this paradox.

 

[rcgldr]

A turbulent wake from a convex surface occurs because of viscosity and inertia issues. If there was very little viscosity, you'd have a huge near stagnant "boundary layer" to fill in what would otherwise be a void if the fluid doesn't follow a convex surface because of inertia issues.

In the real world, on a convex surface, there's a boundary layer that gets effectively thicker and separates with distance from leading edge of the surface. That boundary layer may be nearly laminar at low Reynolds numbers. Although the flow is laminar, the effective boundary layer separates and ends up thicker that it would if it was turbulent, so some low Reynolds number air foils deliberatly trip up the boundary later to trigger turbulent flow, which costs energy at the trigger point, but reduces the effective profile drag by making the effective boundary later thinner. This is mostly an issue for gliders, which rough up the surface of a wing or use turbulator strips.

Although the wiki article diagram shows the turbulent portion of the boundary layer to be thicker, the over thickness would be smaller if the transition to a turbulent boundary layer occurred sooner (reducing separation which isn't shown, since the diagram is of a flat surface):

http://en.wikipedia.org/wiki/Boundary_layer

As mentioned some gliders either rough up the surface of a wing or use turbulator strips:

http://en.wikipedia.org/wiki/Turbulator