Production-limited DDES of turbulent flow and opposed mixed convection in a vertical concentric annulus

This paper conducts a numerical investigation of turbulent and mixed convection flows within a vertical concentric annulus (VCA) at a Reynolds number (Re) of 26,600, which are pivotal in many engineering applications, such as heat exchangers and chemical reactors. It originally evaluates the performance of the walladapting local eddy -viscosity (WALE) model which is an LES model, and two delayed detached -eddy simulation (DDES) models, namely the improved DDES (IDDES) and the production -limited DDES (PL-DDES) models, in simulating developed turbulent flows in a VCA. Among these, the PL-DDES model demonstrates superior accuracy in predicting time -averaged turbulent flow characteristics, as validated against experimental data, outperforming both the IDDES and WALE models. Subsequent simulations of opposed mixed convection flows with varying Buoyancy number (Bo = 0, 0.8, 3.2) utilizing the PL-DDES model add depth to our understanding of how buoyancy affects turbulent flow and heat transfer in a VCA. The results reveal that increases in Bo lead to reduced skin friction coefficients on the inner and outer walls. Conversely, the Nusselt number (Nu), wall -normal turbulent heat flux, and Reynolds shear stress near both walls are augmented. Additionally, quantitative analyses of these mixed convection flows indicate a more pronounced influence of Bo on the flow field compared to the thermal field, particularly in the outer wall region, underscoring the significant impact of buoyancy effects on convection dynamics.