DOI: 10.1615/TSFP5
DIRECT NUMERICAL SIMULATION OF TURBULENT CONVECTION IN A RECTANGULAR RAYLEIGH-BENARD CELL
ABSTRAKT
In the present study Rayleigh-Bénard convection within a rectangular cell is analysed. Turbulent Rayleigh numbers up to Ra = 6.0 × 108 have been simulated using Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) employing the tensor diffusivity model by Leonard and Winkelmans (1999). The effective exponent of the Nusselt-Rayleigh relation is found to be 0.284 which matches theroretical and experimental predections of 2/7 (~ 0.286) very well. Furthermore, the thermal dissipation rate distribution is investigated based on the approach by Shishkina and Wagner (2006). The distribution function is found to consist of three distinct regimes featuring the thermal turbulent background, the plumes and the conductive sublayer. Two functions are defined to approximate the distribution of the turbulent background and the conductive sublayer, and hence limits could be defined for the integration of the three regions. With these limits it is possible to quantify the respective contributions of the different parts of the flow field showing that the contributions of the turbulent background up to Ra = 6.0 × 108 are very small but increse rapidly, once a fully developed turbulent field is established. For the highest simulated Rayleigh number it occupies more than 80% of the fluid volume.