text: It is important to note, that negligible viscosity can no longer be assumed near solid boundaries, such as the case of the airplane wing.  In turbulent flow regimes (Re >> 1), viscosity can typically be neglected, however this is only valid at distances far from solid interfaces.  When considering flow in the vicinity of a solid surface, such as flow through a pipe or around a wing, it is convenient to categorize four distinct regions of flow near the surface:
  * Main turbulent stream: Furthest from the surface, viscosity can be neglected.
  * Inertial sub-layer: The start of the main turbulent stream, viscosity has only minor importance.
  * Buffer layer:  The transformation between inertial and viscous layers.
  * Viscous sub-layer: Closest to the surface, here viscosity is important.
  Although these distinctions can be a useful tool in illustrating the significance of viscous forces near solid interfaces, it is important to note that these regions are fairly arbitrary. Assuming inviscid flow can be a useful tool in solving many fluid dynamics problems, however, this assumption requires careful consideration of the fluid sub layers when solid boundaries are involved.