Mixing in the planar turbulent wakes in passively stratified medium

The flow pattern in the planar turbulent far wake past a body in a passively stratified medium is investigated by applying a mathematical model including the following features: Rodi’s algebraic approximations for Reynolds stresses, the differential equation for transfer of a defect of the mean velocity longitudinal component, the balance of the turbulence energy and its dissipation rate, fluid mean density defect, vertical component of the mass flux vector, and the equation for variance of the turbulent fluctuations of density transfer. The far wake approximation is taken for this problem. The paper discusses an issue of the local-equilibrium truncation taken for the two last equations. We compare the solutions of self-similar degeneration of the density field characteristics for a case of a classical turbulent wake behind a towed cylinder and for a case of momentumless turbulent wake. The results of numerical experiments were a foundation for interpreting the observed significant error while using the locally-equilibrium truncation of equation for the density fluctuations variance transfer.