The high-Re far wake of a slender body and the effects of density stratification

TL;DR

This study investigates the far wake of a slender body at high Reynolds number using hybrid simulations, revealing unique decay behaviors and the influence of stratification on wake dynamics and universality.

Contribution

It provides the first detailed analysis of the far field of a slender body wake at high Reynolds number and examines how stratification affects wake decay and initial condition retention.

Findings

Wake decay rate differs from bluff-body wakes.

Stratification influences the wake's evolution at different Froude numbers.

Far wake retains information of initial conditions.

Abstract

The high-Reynolds-number wake of a slender body with a turbulent boundary layer is investigated using a hybrid simulation. The wake generator is a 6:1 prolate spheroid and the Reynolds number based on the diameter $D$ is $Re = 10^5$. The transition of the unstratified 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 characterized by the presence of broadband turbulence. The simulations show that these particularities alter the decay rate of the wake significantly and challenge the notion of universality -- the idea that far from the body all turbulent wakes decay at the same rate. The influence of stratification in the wake is also studied at Froude numbers $Fr=U_\infty/ND=2$ and $10$. The results imply that the onset of buoyancy effects depends on the wake generator and that the far wake retains information of the initial conditions.