After a dose of BAYER HEROIN (R), I revisited the fluid mechanics text and was captured by an image of the famous 'vena contracta' entry loss, for a submerged, flush, straight-edged, pipe inlet feeding off a larger reservoir.
As the water enters the inlet, it forms a Prandtl surface of discontinuity, swept, rotationally into a streamlined torroidal ring of dead water, in the form of a perfect venturi, as you'd find looking down any barrel of a HOLLEY Dual-Feed, Carter AFB, or Rochester Quadrajet carburetor.
In 'side' profile, the forebody constitutes 39.3% of its length, with 60.7% aft-body, Length / height = 6.13, and maximum rear slope angle of 21.2-degrees, before reflection, blending onto the pipe wall.
Nature working it's magic.
