Can a brick 'fly' (glide)?
Yes, it can (but not in an optimal way)*. That is why aerodynamics has very little to do with curvatures, rounded leading edges, smooth surfaces, sharp trailing edges, and other embellishments; these are all just makeup! In fact, the word "aerodynamics" etymologically means "air in motion," so a turbulent fluid is more aerodynamic than a laminar one from a kinematic point of view. So, strictly speaking, a car or plane designed in the 50's or 60's is more aerodynamic than a newer one. This is not just a word game, a philosophical question, or to sound woke. In order to try to understand or explain a thing, it should be named as precisely as possible, avoiding the use of veiled terms, most of which focus on oversimplifying a complex phenomenon by trying to give only quick answers, leaving aside formal justifications.
In this order of ideas, anything can fly/glide with sufficient velocity! Exactly such a term should be considered as the real cause of everything that has been attributed to the mechanism of lift generation by various hypotheses, theories (and pseudo-theories) implying reacting forces, air downwash, pressure difference or circulation-vorticity. Aerodynamics is rude, not the pretty girl of fluid dynamics! That is why trying to understand it from a smooth-flow perspective, for instance, from an "aerodynamically" optimized surface designer's point of view, is not the best way to try to understand it more deeply. Strictly speaking, laminar fluid (defined as perfect layers flowing on top of each other) does not exist naturally in aerodynamics, since there is always friction (shear layers) between air molecules and those of the surface or other fluid molecules, among other reasons due to the fact that perfectly smooth surfaces do not exist in reality. Therefore, micro-vortices of different scales (from molecular size!) are always generated (mixed and amplified; see Kelvin-Helmholtz instability) from the first "contact" between both fluid and solid surface and then barely diffused by a relatively low viscosity. Even on a "perfectly" smooth surface, curvatures lead to flow separation (with its associated vorticity!), since the viscous effect is not relevant under high Reynolds number conditions. At this point, the idea of a laminar fluid with vorticity is not compatible with the well-known oversimplified explanation in aerodynamics, right? Well, now it does.
And where am I going with such exaggerated precision? In short, the boundary layer (laminar, transitional, and turbulent) is nothing more than a detached flow, but it is damped by the fluid viscosity, which acts mainly tangentially to the surface. I mean, it should be treated and understood from a detached flow perspective, just like aerodynamics (and fluid dynamics!) in general, without enforcing its level of attachment (a viscosity model should regulate it automatically, without any a priori assumption). Remember, aerodynamics is crude. By the way, why do most aerodynamicists talk about laminar/attached fluids ("laminar BL") under high Reynolds number conditions?** Where is it in their experimental tests? (see next video).
In the previous example, a macro-scale "attached" fluid is present only at the bottom. Already from the first second (probably about 2 degrees in AoA) the fluid in the upper part is partially detached, including diffused vorticity as a gray cloud! Thus, from this perspective, all objects immersed in a fluid generate a cloud with different scales of vorticity in the surrounding area (which can become turbulent under certain conditions; this happens even in a flat plate without any incidence!) This is precisely the approach taken in [1], a velocity-vorticity*** method based on a circulation detached from the entire surface, which is capable of capturing not only lift but also drag 'forces' and pitching moment with outstanding precision for simplified geometries. Finally, its extension to three-dimensional thick bodies should lead to the knowledge of the real cause of hydro/aerodynamic force generation: the velocity field induced by the full cloud evolution of detached vorticity, a brute force approach that allows to understand a crude phenomenon.****
Among all the known theories that try to explain the lift generation mechanism, the circulation/vorticity approach seems to be the only one with a solid mathematical foundation, based on a well-established (but partially misinterpreted [2]) Potential Flow Theory, which, compared to Bernoulli's (a subtraction) or Newton's (a change of sign) approaches, seems extremely complicated or too abstract to understand. Perhaps that is why it has not yet been the most popular explanation with the public. However, this does not mean that the work of historical scientists such as Lanchester, Prandtl, Helmholtz, Kelvin, Kutta, Zhukovski, Falkner, Weissinger, Batchelor, Chorin, Belotserkovski, Lewis, Katz, Cottet, Leonard, Winckelmans, Kamemoto or Gharakhani and more recent researchers with notable contributions to the field of theoretical hydrodynamics, potential and vortex methods must be forgotten simply because some minds want to understand complex phenomena through simple "physical" explanations (or simplified models riddled with assumptions); that is why mathematics was developed: to explain physics in a formal and sufficient way; mathematics are also crude.
Something to think about: Are the lift and drag really forces? Are not they just the components of the resultant? So does it make sense to try to explain how only one of them is produced, assuming that both are independent?
*I really hope that all readers are able to understand this by common sense, without having to prove it by an expensive wind tunnel test, a precise CFD simulation, or an analytical demonstration.
**In any case, it might be valid for extremely low Reynolds numbers (e.g. microfluidics). For high-Re conditions (millions, in practical aerodynamics), its length is at best a few centimeters along the wing!
***The pressure field is decoupled from the flow solution, so it cannot be a justification for any flow attachment ('favorable pressure gradients') or detachment ('adverse pressure gradients'); the cause of such phenomena is the velocity field! Pressure is only a consequence of velocity, not vice versa (see the dynamic pressure definition!).
****It could be explained to the public that objects (rocks, bricks, elephants, airplanes or whatever) are able to 'fly' because they float through a cloud of whirls that surrounds them. Besides, it sounds like poetry! Aerodynamics was not so crude after all...
[1] Journal article: The Full Non-linear Vortex Tube-Vorton Method: the pre-stall condition | Advances in Aerodynamics | Full Text (springeropen.com)
[2] Journal article: The Full Multi-wake Vortex Lattice Method: a detached flow model based on Potential Flow Theory | Advances in Aerodynamics | Full Text (springeropen.com)
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