ON THE MODELING OF HOMOGENEOUS TURBULENCE IN A STABLY STRATIFIED FLOW

The decay of incompressible, homogeneous turbulence in a stably strati fied medium is investigated. A conventional high-Reynolds-number, two- equation model with suitable improvements for buoyancy effects is used to calculate the velocity field, while an explicit algebraic heat-flu x model that depends on the velocity held and the transport of the tem perature variance and its dissipation rate is invoked for the temperat ure field. The model thus derived could account for buoyancy flux and streamwise heat transport correctly and is used to investigate the dec ay of grid generated turbulence in a stably stratified medium. This cl ass of flows displays countergradient transport of the vertical turbul ent heat Aux. Flows with buoyancy frequencies ranging from 0 to 2.42 a re calculated. The results are compared with experimental data as well as with the calculations of a constant turbulent Prandtl number model , an algebraic-flux model and a second-order closure. The present mode l is found to be capable of correctly reproducing the countergradient heat transport phenomenon and the turbulence decay characteristics ove r the range of buoyancy frequency studied. However, the countergradien t heat transport region is not captured by the algebraic flux and the constant turbulent Prandtl number model. Furthermore, the present resu lts are in good agreement with data and with the predictions of a seco nd-order closure. (C) 1995 American Institute of Physics.