With some insane amount of work could be done in ilustrator, with some real life photos for reference.

But they are more easity done taking a photo... you gessed... Ink on a water tank.

https://www.google.com/search?q=ink+on+a+tank+photo+tutorial

They also can be done in 3D with a specialized particle generator and render engine: https://www.afterworks.com/FumeFX/Overview.asp

or try blender

• https://www.google.com.mx/search?q=blender+smoke

• https://www.blender.org/manual/pt/physics/smoke/index.html

With some insane amount of work could be done in ilustrator, with some real life photos for reference.

Here is a first attempt using a Mesh fill on Corel. But as you can see this will become extremely complex...

But they are a heck more easily done taking a photo... you guessed... Ink on a water tank.

https://www.google.com/search?q=ink+on+a+tank+photo+tutorial

They also can be done in 3D with a specialized particle generator and render engine: https://www.afterworks.com/FumeFX/Overview.asp

or try blender

• https://www.google.com.mx/search?q=blender+smoke

• https://www.blender.org/manual/pt/physics/smoke/index.html

I really would not waste time doing it natively in Illustrator. Of course, you can vectorize it or trace it after you have a base image. But... That is cheating :o).