The Q-criterion is how fluid dynamicists see a turbulent flow's skeleton. Split the
velocity gradient into strain S (stretching) and rotation Ω (spin); then
Q = ½(‖Ω‖² − ‖S‖²). Where Q > 0, rotation wins — you are inside a
vortex tube. Here that scalar is computed on a grid from the Helix Noise velocity and its
isosurface is extracted by marching cubes, tinted by helicity sign
(teal right / amber left).
Raise coherence and watch a formless tangle condense into distinct tubes. Drag to orbit.
The Q-criterion is the standard way to visualize a flow's vortex skeleton: it isolates the
regions where rotation Ω beats strain S. Because Helix Noise gives an analytic,
divergence-free velocity field, computing Q on a grid and extracting its isosurface
is cheap and exact — a direct window onto the coherent structures the coherence
knob builds.