For stills or animation ya could just put the flames in the renders or add them in post.

For a still ya could just paint it in post.

For anamtions app's like after effects.
I'm sure there' more then a few CGI flames app's out there.
Blender can make Flames.

 

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The Artist that will fight for decades to conquer their media.
Even if you never know their name ,your know their Art.
Dark Sphere Mage Vengeance