[riquelmebk]

Hi all,
I have some questions about Separation of inviscid core region and boundary layer.
For a Transient axisymmetric Poiseuille flow, the liquid is viscous, the velocity near the wall is zero due to non-slip condition, and the velocity of fluid in the centerline is the largest. Why the region near the centerline is inviscid core while the region near the wall is viscous?
For a viscous region, is it true that it's difficult to change the motion direction of liquid, compared to inviscid region?
Can the model in the figure 2 explain the physical process in the figure 1?
Thank you very much!