Numerical study of the effects occurring near a circular cylinder in stratified fluid flows with short buoyancy periods

Flow around a two-dimensional circular cylinder of a stratified fluid with periods buoyancy $T_b = 25.2$ and $6.28$ sec is studied numerically over a wide range of Reynolds and Froude numbers. It is found that in the presence of a perturbation ahead of a cylinder which moves downstream with increasing Reynolds number, the salinity isolines have the shape of a semi-circular comb with sharp teeth. The shape change of the attached waves and the occurrence of fluid layers of different densities in the cylinder wake are studied. In flows with a buoyancy period $T_b = 6.28$ sec at Reynolds numbers $\mathrm{Re} < 60$ , stagnant zones are found in the cylinder wake, and at $\mathrm{Re}>60$ , these zones are absent.