CFD simulation of heat transfer at surface of bluff bodies in turbulent boundary layers : evaluation of a forced-convective temperature wall function for mixed convection

Accurate predictions of convective heat transfer are essential in building-engineering and environmental studies on urban heat islands, building energy performance, (natural) building and inter-building ventilation and building envelope durability and conservation. In computational fluid dynamics (CFD) studies of these applications, wall functions are mostly used to model the boundary-layer region. Recently, an adjusted wall function for temperature (CWF) has been proposed (Defraeye, T., Blocken, B., Carmeliet, J., 2011a.). This CWF was intended for forcedconvective heat transfer at surfaces of bluff bodies, such as buildings in the atmospheric boundary layer (ABL). This CWF provides increased (wall-function) accuracy for convective heat transfer predictions and can be easily implemented in existing CFD codes. As ABL flow around buildings is often in the mixed-convective regime, the CWF performance is evaluated for situations with mixed convection in this paper. The CWF accuracy for mixed convection (~16% for the convective heat transfer coefficient, CHTC) is also much better than standard wall functions (~47% for the CHTC), but is Richardson-number dependent. The CWF approach can therefore significantly improve the accuracy of forced- or mixed-convective heat transfer in large-scale building-engineering or environmental studies, which are bound to rely on wall functions, but where accurate convective heat transfer predictions are required.