If friction is assumed to be zero, this thing can be assumed to be non-existent, allowing free slip of a fluid along the surface of a pipe.
The equation for a flow in this thing can be solved using the momentum integral method of Kármán and Pohlhausen. Using non-dimensional variables, two partial differential equations describing the flow for this thing can be transformed to a single ordinary differential equation by the Blasius method. The first physicist to derive equations for the flow of this thing was Ludwig Prandtl. Vortex sheets that are not free can diffuse to form this thing. For a sufficiently high Reynolds number, a flow can be divided into an inviscid flow and a flow named for this thing. If friction is assumed to be zero, this thing can be assumed to be non-existent, allowing free slip of a fluid along the surface of a pipe. For 10 points, identify this "layer" of a fluid, near a bordering surface, where viscosity effects are important.
The equation for a flow in this thing can be solved using the momentum integral method of Kármán and Pohlhausen.
boundary layer [or boundary layer after "layer" is read]