Which came first: the chicken or the egg? velocity or pressure?
The pressure field seems to be the quick answer to almost any question in aerodynamics (and fluid dynamics), from the cause of the lift "force" on an airfoil and wing tip vortices to more specific aspects such as fluid separation or the generation of vorticity on a surface. For example, the term "adverse pressure gradient" (it sounds so smart) is often used by those trying to justify the cause of fluid separation behind an aerodynamic body. According to a recent survey conducted in a LinkedIn CFD group (see Fig. 5), it is clear that two-thirds (36/53) of the participants believe that there is no direct cause-effect between velocity and pressure fields since both are coupled, while the remaining one-third (17/53, including me) mark a causal in one or the other direction (velocity causes pressure or pressure causes velocity). With such disagreement, this uncertainty must be considered an open question. Therefore, in this short blog post, I will try to justify, from b