As the boundary thickness grows what happens to velocity gradient and shear stress
Answers
Before the fluid gets to the leading edge of the plate, all the fluid is flowing freely. As some fluid starts passing close to the leading edge, that fluid is slowed down by viscosity. But the fluid farther out is still moving along freely. That slow fluid near the plate, as it slowly moves downstream, is pulling backwards on the faster moving fluid above it. Now that fluid gets slowed down too. But it is also still travelling along parallel to the plate. So it’s further downstream. It is now slowing the fluid even farther out. That farther out stuff was moving freely until it got this far downstream above the plate. But now it is slowed down. Any fluid that is slowed down is now counted as being in the boundary layer. So as you go farther downstream along the plate, more and more fluid is involved in the boundary layer because the slowing effect has finally worked its way out to the point in the free stream. Therefore tne boundary layer is thicker than it was upstream.