The phrase "swirl effect" refers to a visual or physical pattern that resembles a swirling or rotating motion. It can be used to describe anything that has a twisting or spiraling appearance. Full definition
I add mine while it's still warm to give it a chocolate swirl effect. (thebettyrocker.com)
The mermaid skirt and train have godet panels, creating a beautiful swirling effect when you walk in this gown. (ianstuart-bride.com)
«The photo of the damaged board is massively doctored with a lot of swirl effects,» wrote another, «which is very easy to see when you know silk - screened lines [on the circuit board between the memory modules] are not supposed to be curved.» (scientificamerican.com)