Simulation of scale-resolved mixing of passive scalars in waves and turbulence

The accuracy of global circulation models partly relies on understanding the dynamics at the coupled atmosphere-ocean interface. Related current research efforts focus on a range of aspects, including the quantification of energy budgets, an understanding of wave growth mechanisms as well as other processes relating to the interaction between waves and ambient turbulence of the upper ocean. The latter is particularly important for the understanding of gas transports close to the surface in the presence of old and long waves (swell). Reported efforts are based on a previously introduced hybrid scale-resolving, numerical method that fully resolves both the air and water phase at realistic Reynolds numbers [Phys. of Fluids, Vol. 35 (7): 072108]. In this context, we enhanced the model by a passive scalar transport procedure to observe the transport of an arbitrary number of passive scalars close to the surface within the upper ocean layer. The presentation will address the treatment of numerical issues, primarily related unintended numerical diffusion through the interface, and explain the layout of a method to obtain accurate results for different wave-turbulence scenarios. Data processing follows experimental approaches [Journal of Fluid Mechanics, Vol. 962: R1], thereby supporting future joint numerical/experimental studies. Results display wave effects on both the turbulence and the scalar transport close to the surface. In particular, enstrophy and turbulent kinetic energy (TKE) are affected in the vicinity of surface waves. The developed two-phase flow model proves to be a promising approach for future collaborative experimental/numerical studies of transport processes in this highly dynamic domain.