This isn’t a computer-generated image. It’s an actual picture of what happened when NASA decided to test the air flow around an F-18 by putting a model plane, and a lot of dye, in a water tunnel.
These images were created at the Dryden Flight Research Center, back in 1985. Specifically, they were created in the Dryden Water Tunnel. NASA had a procedure for simulating, and visualizing, the flight of a air craft without endangering the air craft:
“Water is pumped through the tunnel in the direction of normal airflow over the aircraft; then, colored dyes are pumped through tubes with needle valves. The dyes flow back along the airframe and over the airfoils highlighting their aerodynamic characteristics. The aircraft can also be moved through its pitch axis to observe airflow disruptions while simulating actual flight at high angles of attack.”
The procedure is used to check for vortices, swirls of air that might drag the plane back or knock it around.