Flow over a square

Particles that only collide and stream, and a square in their way. Push the Reynolds number up and watch the wake come alive. The whole solver is below (… lines).

The entire solver

Flow runs left to right. The top, bottom and inlet are walls moving with the stream, and the outlet copies populations from upstream. Below Re ≈ 50 the wake is steady, and above it the wake sheds. At the top of the range the lattice is far too coarse to be accurate, but it stays stable and keeps swirling. Research codes add curved walls, multiphase flow, GPUs and much more.