Direct and large eddy simulation of the transition of two- and three-dimensional plane plumes in a confined enclosure
The authors investigate the free convection flow induced by a line heat source in a confined geometry. The buoyancy forcing of this flow is characterized by Rayleigh number, Ra, which is chosen in the range where an intermittent spatial transition from laminar to turbulent flow takes place. The governing non-dimensional equations are solved numerically using a finite volume method in the case of air flow, i.e. the Prandtl number \(\text{Pr}=0.71\) and \(\text{Ra}= 10^{10}\). For the numerical simulation, the authors use the direct numerical simulation (DNS) and large eddy simulation (LES) schemes. First, they consider a two-dimensional representation of this flow at resolution of \(195^2\). Next the three-dimensional case at resolution of \(195^3\) has been treated. The three-dimensional simulation reveals a symmetrical time-mean recirculation which covers the domain above the heat source. The LES method for the same flow is carried out at a resolution of \(45^3\). There are many interesting results reported in this paper, but we mention here only the following ones: 1) the time-mean turbulent flow which arises under transient conditions shows a symmetrical profile. All fluctuations have their maximum near the top wall at the centre of the box. In particular, the fluctuations in the axial direction show a relatively sharp increase just below the top wall; 2) On the average, most of LES computations produce a solution which is similar to the DNS solution. Especially, relatively simple equilibrium models lead to a good agreement between LES and DNS.
transition from laminar to turbulent flow
scientific article; zbMATH DE number 1502272