On the dynamics of axisymmetric turbulent separating/reattaching flows

The present work focuses on the intrinsic properties of an axisymmetric separating/reattaching flow. A numerical simulation of a compressible flow over a cylinder extended by another cylinder of smaller diameter is performed at a Reynolds number based on free stream velocity U∞ and on the diameter of the larger cylinder D of 1.2×106. Statistical and fluctuating properties are scrutinized and compared with the available experimental data. Especially, experimental wall pressure coefficient and rms pressure fluctuations are well-reproduced by the simulation. A large scale coherent motion associated to fD/U∞≈0.2 rules the organization of the flow. Moreover, these properties are linked to a linear stability analysis coupled with a two-point correlation analysis unveiling the major importance of highly coherent antisymmetric modes in the flow behavior. Finally, the axisymmetric body dynamics seems to be led by a significant absolutely unstable area suggesting a global instability mechanism.