LES of fluid and heat flow over a wall-bounded short cylinder at different inflow conditions

We report on LES studies of flow patterns, vortical structures and heat transfer in flows over a short single cylinder of diameter D placed in a plane channel of height h=0.4D in which the bottom wall is heated. The Reynolds number of 6150, based on D, corresponds to the water experiments reported by Sahin et al. (2008). For the basic computational domain of 24x14x0.4D three different inflow conditions have been considered: a non-turbulent flow with a uniform initial velocity developing along the channel (NT), a fully developed channel flows (FD) (generated a priori) and periodic conditions (PC). The latter boundary conditions have also been considered for two shorter domain lengths of 6D and 3D corresponding to a cylinder in a compact matrix. For the long domain, despite the length of the channel of 9.5 D before (and after) the cylinder, the inlet conditions show strong effects on the formation and evolution of the multiple vortex systems both in front and behind the cylinder, influencing significantly also friction and heat transfer. Simulations show some agreement with experimental data though the comparison is impaired by the uncertainty in the experimental inflow conditions. For the shortest cylinder spacing the wake never closes and the flow shows enhanced unsteadiness and turbulence level. Interestingly, the comparison for the same short domain (3Dx3D) using the mean temperature at the inflow to this domain as a reference shows the lowest average base-wall Nusselt number in the PC 3D case that corresponds to compact heat exchangers.