Laboratory, numerical and theoretical modeling of a far wake flow in a stratified fluid

A laboratory study and direct numerical simulation (DNS) of far wake flow in a stratified fluid are performed. The laboratory study employs the PIV technique to measure the velocity field in a wake behind a towed sphere at high Reynolds and Froude numbers. The DNS parameters and initialization are prescribed in accordance with the experimental data, which allows a direct comparison between numerical and experimental results. The results of the DNS and the laboratory experiment are compared with predictions of a theoretical model, which considers the wake as a quasi-two dimensional turbulent jet flow with the main mechanism of evolution associated with transfer of momentum from the mean flow to quasi-two dimensional sinuous disturbances growing due to hydrodynamic instability. The time evolution of the wake axis velocity and its width obtained within the framework of the model is in good agreement with the experimental and numerical data

Turbulent Transport in a Stratified Shear Flow

Within the framework of the theory of unsteady turbulent flows in a stratified fluid, a new parameterization of the turbulent Prandtl number is proposed. The parameterization is included in the k-ε-closure and used within the three-dimensional model of thermohydrodynamics of an enclosed water body where density distribution includes pycnocline. This allows us to describe turbulence in a stratified shear flow without the restrictions associated with the gradient Richardson number and justify the choice of closure constants. Numerical experiments, where the downward penetration of turbulence was considered, confirm the advantage of the developed approach in describing the effects neglected in the classical closures