Large Eddy Simulations of Turbulence under Internal Solitary Waves of Depression

The bottom boundary layer (BBL) under an internal solitary wave (ISW) of depression is examined using highly resolved, spectral multidomain penalty-method based, Large Eddy Simulation. The focus is on the three-dimensionalization of the initial shear-instability-driven near-bed vortex wake in the lee of the wave and on the downstream formation of fully developed turbulence. When the ISW propagates into quiescent water, the near-bed vortex wake forms only when the separated BBL is persistently perturbed in the form of localized volumetric forcing. In addition, the near-bed wake three-dimensionalizes but does not become turbulent. When the ISW encounters an oncoming barotropic current, a spontaneous (no perturbations required) complex structural transition to turbulence gives rise to a fully turbulent self-sustained near-bed wake upstream of the wave. Preliminary quantitative results on the turbulent BBL serve as the springboard for a more detailed forthcoming study.