Right now, I am programming the engine plumes for a game called Spaceflight 3D, or basically a better version of KSP2 that my team of developers are working on. Mainly to be made for my company to simulate our spacecraft in flight and orbits.
For the engine plumes, I want them to look like this example: 
This is the exhaust plume of a Falcon 9. As you can see, they expand outwards convex. Can someone tell me a method to code it. I intend to make the engine plumes animations, then use the same logic for every plume for the expantion. Will changing scale be enough? Or has it to be a separate piece of code on its own?