Analysis of the the exterior convective heat transfer coefficients of a cubic building with CFD.

Wind-induced convection at the exterior surface of specific building components or constructions has a noticeable effect on the heat transfer in the building envelope. Hence a proper knowledge of the convective heat transfer coefficients (CHTC) can improve the accuracy of numerical heat transfer modeling. In this paper, the forced CHTC on the surfaces of a cubic building is studied with CFD. Steady RANS (Reynolds-Averaged Navier-Stokes) simulations provide, for each facade, correlations of the surface-averaged transfer coefficient with the wind speed at a height of 10 m. These are compared with existing correlations. Results show a distinct variation of the values of the coefficient over the facade and significant differences are found between the surfaceaveraged transfer coefficients of the facades. RANS simulations are also compared with unsteady simulations with the Detached-Eddy Simulation (DES) model. The predicted transfer coefficients for DES and RANS are found to differ both in magnitude and distribution over the facades. Significant differences are found for the value of the CHTC on the windward facade which is partially attributed to the rather simplified inlet conditions that are used for DES. Nevertheless, a good similarity is found in the distribution over the windward facade for all models. In contrast to RANS, DES does incorporate the unsteady nature of the separated flow in the distribution of the heat transfer coefficient. This is clearly manifested in a more uniform and relative high CHTC on the leeward facade.