Originally Posted by
Owain Glyndwr
No problem with Sir Isaac and changes to the integrated pressures normal to the surface, but the measurements (NACA TN 1095 again) show that the pressure changes are such that the pressures on the upper surface are barely affected by the presence of ground whereas the pressures on the lower surface increase substantially in a manner that indicates that the flow over the lower surface is retarded.
That is why I'm still convinced that the downwash behind the wing leads to a 'choking' of the mass stream underneath the wing as it displaces the streamlines normally exiting along the lower surface downward toward the ground which themselves are displacing other streamlines.
As the ground puts a fixed barrier to this mutual displacement, the effective freestream area behind the TE is reduced.
Assuming mass flow = free stream speed x effective free stream area this will reduce mass flow and thus velocity underneath the wing, leading to increased static pressure on the lower side.
Sorry for defending Mr. Bernoulli again.
