BUDGETS OF TURBULENT STRESSES AND FLUXES IN A VERTICAL SLOT NATURAL-CONVECTION FLOW AT RAYLEIGH RA=10(5) AND 5.4 10(5)

A direct numerical simulation (DNS) of natural turbulent convection in a differentially heated infinite vertical slot has been computed with a mixed finite difference/Fourier code at Rayleigh numbers of R(a) = 1.0 10(5) and R(a) = 5.4 10(5). A database containing up to second-ord er budgets has been collected, and the physics of the Reynolds stresse s and turbulent heat fluxes is analyzed in light of the relevant conse rvation equations. Unusual features are the negative production terms and countergradient turbulent transport. Near-wall flow characteristic s are strongly influenced by transport of quantities from the core of the ''Couette flow'' where most of the turbulence is produced. A fairl y simple second-moment closure, relying on elliptic relaxation instead of damping functions for near wall effects, is found to perform fairl y well on a global scale. Although the modeling approach is open for i mprovements if a term-by-term analysis is conducted. (C) 1997 by Elsev ier Science Inc.