High-resolution CFD simulations of forced convective heat transfer coefficients at exterior building surfaces

High-resolution CFD simulations of forced convective heat transfer at the facades of a low-rise cubic building (10x10x10m³) are conducted to determine convective heat transfer coefficients (CHTC). CFD model validation is performed based on wind tunnel measurements of the upstream near-field velocity pattern. A particular feature of the CFD simulations is the use of a high-resolution grid with control volumes of only 160 micrometer near the building surfaces to resolve the entire boundary layer, including the laminar sublayer that dominates the convective surface resistance. The study shows that: (1) wind flow around the building introduces a very distinct CHTC distribution across the facade; (2) no significant correlation exists between the CHTC and the local wind speed across the facade; (3) for a reference wind speed of 3 m/s, the laminar sublayer has a thickness of about 1 mm; (4) standard and non-equilibrium wall functions are not able to capture the complexity of wind-induced heat transfer, therefore low-Reynolds number modelling on high-resolution grids is imperative; (5) the CHTC distribution across the windward facade shows some similarity to the distribution of wind-driven rain (WDR), with both parameters reaching high levels near the top edge of the facade. This suggests that also the convective vapour transfer coefficient will be higher at this location and that the facade parts that receive most WDR also experience most intensive drying.