At 3,836 mph, which way does the air flow?

Aerospace engineers extend classical kinetic theory into high-speed aerodynamics, including hypersonic speed, which begins at 3,836 mph or roughly five times the speed of sound. The new study attempt to solve long-standing problems associated with high-speed aerodynamics.

from Top Technology News -- ScienceDaily https://www.sciencedaily.com/releases/2019/03/190312123706.htm