The investigation of turbulence characteristics in an internally-heated unstably-stratified fluid layer

Turbulence characteristics of the hydro- and thermal-fields in an internally-heated horizontal fluid layer are numerically investigated for Rayleigh numbers up to 5 . 10(8) using a finite-difference code for direct numerical simulations. Calculated results indicate significant anisotropic turbulent behaviour and non-equilibrium of turbulent kinetic energy and thermal variance under unstable-stratification conditions. It was found that important turbulence constants are remarkably non-uniformly distributed across the layer and strongly dependent upon Rayleigh and fluid Prandtl numbers. These factors pose the principal difficulty in developing a generic higher order turbulence model for this type of buoyant flows. (C) 1997 Elsevier Science S.A.