where $L$ is a characteristic length, such as the chord length of an airfoil.
If you have ever been told that air molecules must meet at the trailing edge because they split at the leading edge, you have been taught a lie. This "equal transit time" theory implies the air over the curved top must move faster, and via Bernoulli, that faster air creates lower pressure. It sounds neat. It is also . understanding aerodynamics arguing from the real physics pdf
$$\textRe = \frac\rho v L\mu$$
Pressure differences between the front and rear of an object due to flow separation. Streamlining, teardrop shapes, smooth transitions. where $L$ is a characteristic length, such as