Session JH - Turbulent Shear Flows.
MIXED session, Monday afternoon, November 22
Grand Crescent, Westin Seattle
Direct numerical simulations are performed to study turbulent dispersion in stably stratified homogeneous shear flow. In stably-stratified fluids, fluid particles are constrained to stay within a vertical distance of order w/N from their equilibrium density level, where w is the rms vertical component of turbulent velocity and N is the local buoyancy frequency of the fluid. However, molecular diffusion can alter the density of fluid particles which, in turn, alters the equilibrium level about which they oscillate with amplitude w/N. Thus, the vertical flux of density in a stratified turbulent flow is the result of two processes: the first is the vertical displacements of fluid particles and the second is the molecular mixing between fluid particles. These ideas are the basis of the theory of Pearson, Puttock and Hunt (1983), valid for statistically stationary homogeneous turbulence. In the present work, we test these ideas and investigate the presence of mean shear. A range of stratification levels corresponding to subcritical, critical, and supercritical flow conditions, which are associated with growing, stationary, and decaying turbulence, respectively, is considered. Lagrangian statistics are obtained by tracking fluid particles. Results show the effects of shear on vertical and horizontal displacements and the role of mixing.