A thermal similarity model of a curved double-skin façade

Curved double-skin façades (CDSFs) have been widely used as building envelopes that combine the advantages of aesthetic and energy-saving. However, because of its complex structure and airflow, it is difficult to be precisely reduced in experiments and has been barely studied in the existing literature. Hence, a thermal similarity mathematical model for the CDSF is developed and validated by using methods combining CFD and experiments. The validation results show a good similarity between the reduced-scale model and the full-scale model. On this basis, the influence of dimensionless numbers, boundary conditions, size and appearance on the similarity are analyzed. The results show that the similarity improves with the increment of the Reynolds number until it reaches the self-similarity region. And the Grashof number shows a significant impact on the similarity when the Richardson number >1. So, it is necessary to ensure that the Richardson number <1 when the similarity of the Grashof number cannot be guaranteed. Moreover, solar radiation intensities between 200 W/m2 and 400 W/m2 and solar incident angles between 45° and 60° show the best similarity between the reduced-scale model and full-scale model. The scale of the model has a significant effect on the similarity and is recommended between 1/20 and 1/50 for large buildings with CDSFs. Besides, a smaller ellipse aspect ratio shows a better similarity between the two models. Therefore, a scaled CDSF model with ellipse aspect ratios less than 1 exhibits better validity compared to models with the ratio larger than 1.