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

Abstract

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 et al., 2011a). This CWF was intended for forced-convective 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.