[aerohead]

The perspicacious have probably already noticed from smoke-flow imaging that, streamline flow filaments begin to displace from their 'rest' position before the vehicle's nose actually 'arrives'.
They take on the trajectory of Lanchester's pointed 'head', whether or not actually 'pointed.' Figure 4, page- 10.
You're witnessing the Lanchester/Prandtl 'surface of discontinuity.' ( Figure 20, page 30 ).
Fluid ( air ) in the presence of an obstruction, demonstrates a path of least resistance around the obstruction.
And as with Lanchester's 'pointed' nose, later in his book you notice that the streamlines follow the same trajectory if the nose is simply rounded, but also if part of the leading edge is actually removed.( Figure 16, page-27 )
The identical trajectory is maintained.
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If one observes the 'lowest' streamline which passes over a vehicle, and notes the location of where this streamline first diverges from a straight path, the 'length' of this streamline, compared to a distant streamline ( at infinity ), at any position, comparatively, this difference in length establishes the average difference in velocity between the two streams, as both, by definition, reach the same position of longitudinal distance at the same time.
Distance vs Time. d/t
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One will also observe the vertical distance a specific molecule of air will displace from it's rest position, as a function of 'where' it is along the contour of the body, and the 'time' when it's there.
On a 'streamlined' body, in which zero separation occurs, this is extremely important with respect to local pressure.
As a given air molecule resumes it's 'pre-encounter' position, it's essentially regained all it's rest energy ( static pressure ), with the exception of what it lost to friction drag heating of the atmosphere, which due to the viscosity of air, is inescapable.