4 upvotes, 2 direct replies (showing 2)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
How does the physics of air on the smaller scale of insects affect their aerodynamics and flight mechanisms differently than birds or planes?
Comment by GenericUsername2056 at 14/09/2022 at 19:01 UTC
5 upvotes, 1 direct replies
To get an idea, we can look at the Reynolds number. The Reynolds number is a dimensionless number which is great for assessing dynamic similarity in fluid flows (at subsonic speeds, at supersonic speeds you'd also want to match the Mach number). The Reynolds number is defined as:
Re = (ρ L U) / μ
With ρ the fluid density, L the characteristic length (somewhat arbitrary), U the fluid velocity and μ the fluid density. At equal air flow conditions, we can immediately see the difference between an aeroplane and an insect lies in the characteristic length. Because of the much smaller dimensions of an insect, the Reynolds number will be lower as well.
The Reynolds number denotes the ratio of inertial forces to viscous forces acting on a fluid. So a lower Reynolds number means a lower ratio between these two types of forces. For the insect, this means viscous forces will play a comparatively larger role than inertial forces, relative to the case of an aeroplane in the same fluid flow. If inertial forces dominate, the fluid flow will be largely turbulent. Conversely, if the viscous forces dominate, the fluid flow will be largely laminar.
Comment by racinreaver at 15/09/2022 at 21:51 UTC
2 upvotes, 0 direct replies