Stratified wake of a 6:1 prolate spheroid at a moderate pitch angle

The on-body flow and near-to-intermediate wake of a 6:1 prolate spheroid at a pitch angle of $\alpha = 10^{\circ }$ and a length-based Reynolds number, ${Re}_L = U_\infty L / \nu = 3 \times 10^4$ , are investigated using large eddy simulation (LES) across four stratification levels: ${\textit {Fr}} = U_{\infty }/ND = \infty , 6, 1.9$ and $1$ . A streamwise vortex pair, characteristic of non-zero $\alpha$ in unstratified flow over both slender and blunt bodies, is observed. At ${\textit {Fr}} = \infty$ (unstratified) and $6$ , the vortex pair has a lateral left–right asymmetry as has been reported in several previous studies of unstratified flow. However, at higher stratification levels of ${\textit {Fr}} = 1.9$ and $1$ , this asymmetry disappears and there is a complex combination of body-shed vorticity that is affected by baroclinicity and vorticity associated with internal gravity waves. Even at the relatively weak stratification of ${\textit {Fr}} = 6$ , the wake is strongly influenced by buoyancy from the outset: ( a ) the vertical drift of the wake is more constrained at ${\textit {Fr}} = 6$ than at ${\textit {Fr}} = \infty$ throughout the domain; and ( b ) the streamwise vortex pair loses coherence by $x/D = 10$ in the ${\textit {Fr}} = 6$ wake, unlike the ${\textit {Fr}} = \infty$ case. For the ${\textit {Fr}} = 1$ wake, flow separation characteristics differ significantly from those at ${\textit {Fr}} = \infty$ and $6$ , resulting in a double-lobed wake topology that persists throughout the domain.