Experimental balances for the second moments for a buoyant plume and theirimplication on turbulence modeling

The experimental budgets for the transport equations for heat flux and Reyn olds stress are presented for a round turbulent buoyant plume. The pressure correlation terms are deduced as the closing terms and are found to consti tute a substantial part of these budgets. Even though a buoyant plume is in itiated by buoyancy, it is found that the production of heat flux and Reyno lds stress is largely maintained by the mean flow gradients, because the bu oyancy production terms are not as large. The results are used to assess th e local equilibrium assumption, which implies that the production and destr uction terms of the transport equations balance each other. The results are also used to investigate why the mechanical to thermal time scale ratio fo r a buoyant plume is different than the commonly used value. Finally, some simpler models for the pressure correlation terms, which appear in the heat flux and the Reynolds stress equations, are assessed against those deduced from the experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.