HEAT TRANSFER IN LOW-PRANDTL NUMBER FREE CONVECTION FROM INTERNALLY HEATED RECTANGULAR ENCLOSURES

Two-dimensional direct numerical simulations (DNS) were performed for the free convection flow of a low-Prandtl number fluid (Pr=0.0321) in rectangular enclosures with internal heat generation, adiabatic top/bottom walls and isothermal side walls. Three different values of the aspect ratio (height/width of the enclosure) were considered: AR=4 (slender cavity), AR=1 (square cavity) and AR=0.25 (shallow cavity). For each aspect ratio, at sufficiently high Grashof numbers fully chaotic flow was obtained. Results were compared with predictions based on turbulence models of the k-e family. It was shown that turbulence models predicted poorly turbulence quantities (Reynolds stresses and heat fluxes), while yielding a satisfactory agreement with time-averaged DNS