Vortex z = r sin(3θ + t) / 4
Equation: z = sin(3 * atan2(y, x) + t) * sqrt(x^2 + y^2) / 4
atan2(y, x) is the polar angle θ. The factor 3 gives threefold symmetry; adding t spins the arms.
Amplitude grows with r, so the surface flattens at the origin and flares outward — unlike a Gaussian.