Reynolds number effects in stratified turbulent wakes

We report large-eddy simulations of the turbulent wake of a towed-sphere of diameter D at speed U in a linearly stratified Boussinesq fluid with buoyancy frequency N . These simulations are performed using a spectral-multidomain-penalty-method-based incompressible Navier-Stokes solver for Re ≡ UD/ν ∈ {5 × 10, 10, 4 × 10} and Fr ≡ 2U/(ND) ∈ {4, 16, 64}. Increasingly richer turbulent fine structures are observed in higher-Re wakes within the larger-scale quasi-horizontal vortices at later times, when it is commonly expected that buoyancy has suppressed any turbulent motions. Such phenomenology is examined using the (Reh,Fr −1 h ) phase diagram (Brethouwer et al., 2007). The body-based wake Re is the parameter which determines whether the flow can indeed enter the inviscid strongly stratified regime within which the buoyancy-driven vertical shear layers can either sustain existing turbulence or give rise to secondary shearinstabilities and localized turbulent bursts. The duration of the stratified turbulence regime also scales linearly with Re posing questions on the structural nature of the associated turbulence and its strength with respect to any background motions.