Mixing efficiency in shearless, inhomogeneous, and stably stratified turbulence

Large scale simulations of the Earth’s oceans and atmosphere rely on crude parameterizations of turbulent processes using bulk quantities due to the prohibitive mesh resolution required to capture these processes directly. An interesting flow regime useful for evaluating existing models is one in which shearless turbulence, generated in a localized region of space, decays and interacts with background stratification, a scenario common in geophysical settings.



We propose a series of high-resolution large eddy simulations (1 – 8.5 billion mesh points) to investigate this problem with the goal of identifying limitations of popular models of the mixing efficiency and propose improvements that can handle this highly nonlinear regime. The code we will use is a high order incompressible Navier Stokes solver using a combination of pseudo-spectral and compact difference schemes. The flow is driven by a spatially localized body force which generates negligible mean flow. We have run a series of low-resolution cases (2 million mesh points) to validate the forcing method and determine the parameter space of interest which includes the energy dissipation rate, integral length scale, Reynolds number, Froude number, RMS velocities (stream- and span-wise), and turbulence kinetic energy as functions of distance from the forcing layer.