Laminar flow over an airfoil typically occurs at Reynolds numbers below 5 x 10^5, but this is not a strict threshold. The transition to turbulence is influenced by various factors, including the airfoil shape, surface roughness, and flow quality, making it difficult to pinpoint a universal transition Reynolds number. In many cases, transition occurs at Reynolds numbers well into the millions, especially in turbulent wind tunnel conditions. For internal flow, determining the transition Reynolds number is generally simpler, but challenges remain even for basic geometries like flat plates. The discussion emphasizes the complexity of flow behavior around airfoils, particularly the NACA 0012 symmetrical airfoil in CFD simulations.
