Progress towards the Simulation of Very High Reynolds Number Stratified Sphere Wakes

We report our latest progress towards implicit Large Eddy Simulations (ILES) of stratified sphere wakes at body-based Reynolds numbers of Re = 1.6 × 10⁶ and internal Froude numbers Fr = 4. Such a value of Re enables a sufficiently long window of operation of the highly energetic and relatively unexplored Strongly Stratified Regime (SSR ; de Bruyn Kops and Riley J. Fluid Mech. 2019), extending as far as Nt ≈ 500.

Conducting such simulations, under the tenet of resolving as deep as possible into the turbulence dynamic range, involves highly costly simulations with 35 billion grid points performed in parallel on 8,000 cores on DoD-HPC platforms. Beyond leveraging high-accuracy numerical methods, such as Fourier-Galerkin and modal Spectral Element techniques, flow solver development has involved non-trivial effort towards minimizing memory footprint and optimizing code performance.

Beyond state-of-the-art scientific software design, this presentation will also discuss aspects of the efficient generation of initial conditions for Re = 1.6 × 10⁶ body-exclusive wake ILES. Our first results of actually stratified wake ILES at Fr = 4 will then be presented, extending up to times Nt ≈ 50. The initial focus will be on intermediate-to-late wake vorticity field structure, highlighting the significant enhancement of finer-scale granularity at the target Re as contrasted to lab-scale wakes. Finally, the role of Re on stratified wake trajectories on appropriately-defined regime diagrams will be shown.