Dω/Dt = (ω·∇)u — the mechanism driving turbulent energy cascade
Vorticity stretching: the term (ω·∇)u in the vorticity equation amplifies vorticity when a vortex tube is stretched along its axis. Helicity H = ∫u·ω dV is conserved in ideal flow (Moffatt 1969). Vortex tubes are intensified by strain, forming the fine filaments seen in turbulence. The visualization shows helical vortex tubes subject to an imposed strain field, tracking how vorticity magnitude and tube geometry evolve.