Formation of Three-Dimensional Internal Waves behind a Body in Motion in a Stratified Viscous Fluid

A uniform motion of a disk in horizontal direction along its axis of symmetry in a stratified viscous fluid at rest is studied. The disk generates three-dimensional internal gravity waves occupying the entire volume between the disk and the location of its start. The waves are observed using two-color, beta-plus visualization of the vortex flow structure calculated within the framework of the system of Navier–Stokes equations in the Boussinesq approximation. The results of the study complete considerably the earlier-published mechanism of the formation of half-waves above the axis of symmetry of the disk, where emphasis was placed on the periodic process of generation of deformed vortex rings above the location of the disk start. Their generation is due to gravitation and shear instabilities, when the left semi-ring is transformed into a half-wave of depressions or crests, while the right one vanishes with time. In this paper it is established that the left parts of the right odd semi-rings are transformed into the axial parts of the crest half-waves.