High-Reynolds-number wake of a slender body

Abstract

The high-Reynolds-number axisymmetric wake of a slender body with a turbulent boundary layer is investigated using a hybrid simulation. The wake generator is a prolate spheroid and the Reynolds number based on the diameter is. The transition of the wake to a state of complete self-similarity is investigated by looking for the first time into the far field of a slender-body wake. Unlike bluff-body wakes, here the flow is not dominated by vortex shedding in the near wake. Instead, the recirculation region is very small, the near wake is quasi-parallel and is characterised by the presence of broadband turbulence. Until, the wake decay of a slender body with turbulent boundary layer is very similar to the classic high-behaviour,. Extrapolation of this observation to larger has led to the belief that these wakes decay following the asymptotic decay law. Our results show, however, that this is not the case and the wake transitions to a faster decay rate once complete self-similarity is achieved. In this later region (20 < 80), mean and turbulence profiles are self-similar. Furthermore, despite the high global and local Reynolds numbers, the classic hypotheses that lead to the well-known decay exponents are not fulfilled. Instead, turbulent dissipation follows a non-equilibrium scaling and a new decay rate is observed. The transition from to is preceded by the dominance of the azimuthal mode and the emergence of a large-scale helical structure.