Time evolution of the vorticity field for a case of θ = 88.5°. The initial stages show the onset of RT instability, followed by the formation of vortical structures in the shape of bubbles and plumes at 257.6 s. This then transitions to the late nonlinear phase at time 515.2 s, with the formation of small-scale structures due to the increasing shear at the edge of bubbles and plumes. At time 858.7 s, these substructures organize into vortices and other coherent structures, predominantly in the vertical direction.