Fluids & Combustion (real CFD)
Rayleigh–Bénard Convection
heated floor + buoyancy → rolls

Heating the floor and cooling the ceiling of the fluid box spins up convection rolls — warm fluid rises, cool fluid sinks, exactly as in a heated room or a pot of water.
Computed & rendered in pure C# on the frozen OnlyCSharp 1.8 library — animation baked to GIF with the library's own
Gif encoder (no GPU, no ffmpeg, no external packages).