Imagine a boulder in a stream. As the water hits the boulder, it splits around the object. Once it’s passed around, the two flowing streams crash together, creating turbulent conditions that, if visible, would manifest as chaotic whorls and vortexes. This isn’t just true of water. It’s true of all fluids, including air.
The mathematical equations underlying fluid motion — known as the Navier-Stokes equations — are among the most notoriously challenging partial differential equations because in principle they encode complex behaviors similar to the one you just imagined.