A signature of a bluff body in the internal wave field?

Abstract

The wakes of bluff bodies are known to last longer in a stratified fluid than in a non-stratified fluid [3]. However, it was recently found that these wakes show little dependence on the shape of the body, since they are self-preserved [4]. The long lasting wake in fact forgets the initial conditions. Another interesting feature of stratified wakes is that they emit internal waves, which propagate on large distances without being attenuated. In this presentation, we investigate the influence of the shape of a bluff body on the set of internal waves emitted in a linear stratified fluid. At low Froude numbers, the Lee waves are predominant, as in the case of a sphere[1]. They are shown in the following figure in the case of a cylinder, moving from right to left. However, their very complex structures seem to be dependent on the shape of the object, due to the modulation of the amplitude of the various modes by the shape of the bluff body. These results will be compared to the linear theory found by Lighthill [2]