Numerical investigation of breaking internal solitary waves


la Forgia G., Tokyay T., Adduce C., Constantinescu G.

PHYSICAL REVIEW FLUIDS, cilt.3, 2018 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

High-resolution three-dimensional large-eddy simulations are used to investigate the effects of internal solitary waves (ISWs) breaking over a sloping boundary. The lock release method is applied in a two-layer stratified fluid system to generate three different breaking mechanisms (i.e., plunging, collapsing, and surging breakers). The different breaking types are investigated in terms of their effects on the dynamics of the ISW and the interaction of the ISW with the sloping boundary. During each breaking event, the pycnocline region entrains fresher water from the upper layer and saltier water from the lower one. The associated increase of the intermediate density layer also induces changes of the pycnocline water density. This process occurs with a velocity that can be evaluated using the bulk entrainment parameter. We show how the intermediate layer features depend on the ISW shoaling and breaking dynamics and we discuss entrainment in breaking ISWs. The instabilities induced by boundary layer separation allow entrainment of saltier water, while the run-up of the gravity current causes the decrease of the intermediate layer mean density. Simultaneously, the entrained water mixes into the pycnocline region. For all cases, the temporal evolution of the instantaneous mixing efficiency is discussed. The plunging breaker case shows the largest amount of mixing, which is mostly induced by rear-edge overturning in the onshore direction. The largest entrainment is observed in the surging breaker case in response to the large gravity current flowing upslope. The paper discusses how the different turbulent instabilities induced by the ISWs breaking affect the time delay between the times when entrainment of patches of salty and fresh water from the neighboring layers occurs and the time the density of the intermediate layers becomes fairly uniform via mixing. We finally point out that the entrainment parameter and the mixing efficiency describe two different effects of the turbulent instabilities occurring in a stratified fluid in terms of changes of the bulk density profile.