Below is short list of selected resources if you’re studying (advanced) fluid dynamics.
If you’re getting started with fluid mechanics at an advanced level I recommend you the following select resources. I also invite you to check previous posts on fluid dynamics most of which are videos or images of amazing fluid flows.
In a previous post I shared with you an image of milk vortices created in a hot coffee cup. Today I share with you a demonstration of vortex formation using a free jet of air of a speed higher than that (stagnant) surrounding it.
This is one case of fluid instability called the Kelvin-Helmholtz instabilities (KHI) which occurs when two fluids have different velocities. A very popular and practical example of it are sea surface waves which are created due to the velocity difference between the water and wind.
More accurately, the shear force applied by one fluid (air in this case) on the other (water) creates a shear stress in the other fluid which if greater than the surface tension of the second fluid results in the KHI.
It is also common in clouds and on gas planets like Saturn and Jupiter as the following image of Saturn show.