The article explains the physics ... scaled tornado. https://aviation.stackexchange.com/questions/21219/how-does-this-vortex-form-inside-a-jet-engine It is a common phenomenon, though the atmospheric conditions needed to opacify the vortex are less common. Some vortices are deliberate. The chine or strake shown here generates a visible vortex that delays airflow separation at low speed and high angle of attack ... rather useful when taking off and landing. The absence of "source scuzz" shows that a different mechanism is working here. Twisted love!