Fig. 6.

The geometry of the vorticity direction: (A) the 2D vorticity direction $\tilde{\xi }={\left({\xi }_r,{\xi }_z\right)}^T$ and (B) the z-direction component ξ_z computed on the 1,024 × 1,024 mesh at τ₂ = 0.003505, shown on the region [r_l, 1] × [0, z_r], where r_l = 1 − 5.99 × 10⁻¹¹ and z_r = 2.09 × 10⁻¹². The through-plane (θ) component of ξ has a magnitude of order O(10⁻⁶) in the plotting region and hence is negligible.