ABSTRACT
Existing data from Large Eddy Simulations (L.E.S.) of the stratified turbulent wake of a towed sphere over a broad range of Reynolds and internal Froude number are analyzed. The focus is on quantifying the associated vertical momentum transport during the prolonged Non-Equilibrium (NEQ) regime at higher sphere-based Reynolds numbers, Re. During this regime, when vertical motion is commonly assumed to be suppressed by buoyancy, intermittent secondary Kelvin-Helmholtz instabilities and turbulence drive intensified vertical fluxes of turbulent momentum whose magnitude scales with Fr−4/3, where Fr is the internal Froude number. The associated eddy viscosities are found to be as much as ten times larger as their molecular counterpart. At geophysically relevant Re, the transport coefficients in the NEQ regime are anticipated to be even greater, motivating a reconsideration of the parameterization of stratified turbulence in both similarity-based and larger-scale circulation models.
