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e prosegue:
In the real world, lifting flows are never precisely two dimensional, even when we try to make them so, as we do in so-called 2D wind-tunnel testing. It seems like it should be possible to produce precisely 2D airfoil flow in a wind tunnel: Just mount a 2D airfoil model so that it spans the space between parallel tunnel sidewalls. But in reality 2D flow is practically impossible to achieve because of viscous effects on the tunnel sidewalls and in the junctions between the model and the sidewalls, and results of 2D wind-tunnel testing are always questionable to some extent. On many flight vehicles, however, wings are of high enough aspect ratio that the local flow at stations over most of the span behaves at least qualitatively like the 2D ideal. Thus exploring the physics and doing some of our design work in the ideal 2D world makes sense. Even trying to simulate 2D flow in the wind tunnel can be useful in spite of the generally imperfect results. In this chapter, we'll concentrate on nominally 2D flow because it's simpler, and we can learn a lot that is generally applicable.
McLean, Doug. Understanding Aerodynamics: Arguing from the Real Physics (Aerospace Series) (pp.259-260). Wiley. Edizione del Kindle.
Poi mette tredicimila paletti per die i pagine, perchè e come si può usare l'ipotesi inviscida e quando invece ci si deve far ricorso, come per l'uscita del flusso dal ventre nel modo che osserviamo senza che questa si diriga verso il dorso dove c'è minore pressione, evento dove si può anche usare la compressibilità come argomento eccetera.
A un certo punto, salto di palo in frasca, a proposito della circolazione, fa notare :
Really understanding why something speeds up requires looking at the forces.
Che è la chiave per sapere se è nato prima l'uovo o la gallina.
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