Energetics, flux budgets and heat transport in stably stratified turbulence: theory, experiments, simulations and astrophysical applications
by
Prof.Igor Rogachevskii(Ben-Gurion University of the Negev)
→
Europe/Stockholm
122:026
122:026
Description
We discuss physical background of the energy- and flux-budget turbulence
closure based on the budget equations for the turbulent kinetic and
potential energies and turbulent fluxes of momentum and buoyancy. The
closure is designed for stratified geophysical and astrophysical
flows from neutral to very stable stratification. In accordance to
modern experimental and observational evidence, the closure implies
maintaining of turbulence by the velocity shear or other source at
any gradient Richardson number Ri, and distinguishes between the two
principally different regimes: "strong turbulence" at Ri << 1 typical
of boundary-layer flows and characterised by the practically constant
turbulent Prandtl number; and "weak turbulence" at Ri > 1 typical
of the free atmosphere or deep ocean, where turbulent Prandtl number
asymptotically linearly increases with increasing Ri (which implies
very strong suppression of the heat transfer compared to the momentum
transfer). We also discuss resent experimental results on transport
of temperature and velocity fluctuations in stably stratified forced
turbulence. In the experiments in air flow with an imposed vertical
temperature gradient, the turbulence is produced by two oscillating grids
located nearby the side walls of the chamber. We demonstrated that
for large frequencies of the grid oscillations, the temperature field
can be considered as a passive scalar, while for smaller frequencies the
temperature field behaves as an active field. The theoretical predictions
based on the budget equations for turbulent kinetic energy, turbulent
potential energy and turbulent heat flux, are in a good agreement with the
experimental results. Finally we will discuss the results of numerical
simulations and astrophysical applications.
