CFD-CFD coupling: A novel method to develop a fast urban microclimate model

Computational fluid dynamics (CFD) technique is well-known for its powerful capability of modelling the cross-ventilation. CFD is broadly coupled with energy simulation programmes, such as EnergyPlus, to expand its application in building energy calculation. During the coupling process, iterative calculation is required to improve the accuracy of the coupling method, which means the scale of the model should be designed with extra care so that the simulation can be practical in terms of computational cost. A coarse-resolution mesh (here denoted as CFD_c) cannot properly represent the required local environment to study the underlying physics. However, a fine-resolution CFD microclimate model (here denoted as CFD_f), which includes both indoor and outdoor spaces, always requires a large number of cells to capture the complexities of environment; this makes the coupling procedure a challenging problem. This study aims to propose an innovative, high-resolution and computationally cost-effective CFD_f-CFD_cmodel to overcome this gap. The full-scale CFD_fworks in an off-line manner at the preliminary simulation stage and generates detailed flow parameters at the interfaces for CFD_c. At the dynamic stage of the simulation, CFD_cparticipates in the coupling procedure with the other tools, for example, building energy simulation (BES) tool (e.g. EnergyPlus). The coupling of CFD_f-CFD_c-BES is about 200 times faster than an ordinary coupled CFD_f-BES method with a significantly quicker and more stable achievement in the convergence.