SPINNING UP THE FLOW…

How a Flag FluttersFluid streaming past a blunt obstacle can’t stay tidy: above a certain speed it peels off alternating swirls, first one side then the other, forming the staggered von Kármán vortex street — the same trail of eddies that makes flags snap and power lines hum. The journey: rather than solving the fluid equations directly, this uses the lattice Boltzmann method — imaginary particles hop between grid points along nine directions and gently relax toward local equilibrium after each hop. Densities in, swirl out. Colour is vorticity (spin direction), brightness is speed.