What is meant by the term toroidal vortex ?

Question

what is meant by this term and what is its significance during gas turbine combustion?

Answer 1

Also known as a vortex ring. It looks like a smoke ring.

As the plumes of smoke on a smoke rings make that inward rotaion and also giving lift. As in a helicopter the blades suk the air from above and push it below, but around the outer blades there are vortex rings.

I also found some information in wikipedia for you, it has some images!

Answer 2

If I remember correctly an example of a toroidal vortex would be where fuel vapour is injected into the back of an engine which has a re-heat afterburner.

It creates a doughnut shaped mist from its many injectors which in turn get burnt for reheat.