Research of snow drifting on flat roofs with parapets by numerical simulations and wind tunnel tests

Abstract

Compared with flat roofs without parapets, those with parapets often feature a more complex and varied snow distribution. The paper explores the influences of the height of the parapet on snow distribution on flat roofs using numerical simulations (modified Finite Area Element method) and wind tunnel tests. When adopting the modified Finite Area Element method (FAE method), the paper also considers the effect of snow shape variations on roof snow transport. The wind tunnel test and numerical simulation reveal that the distribution of the friction velocity and flow field around flat roofs with parapets change tremendously with the parapet height. As the parapet height increases, the recirculation area behind the windward parapet gradually enlarges and the mean friction velocity of the snow cover decreases. This indicates that higher parapets exert a more significant hindrance to the roof snow drifting in the same direction as the incoming wind, leading to a larger exposure coefficient of flat roof snow load as the parapet height increases. Furthermore, comparing the results under different incoming wind speeds, it can draw a conclusion that the influence of incoming wind speed on the snow load exposure coefficient of flat roofs with parapets decreases as the parapet height increases. Additionally, by studying four different spans of flat roofs with parapets, it is observed that the threshold friction velocity on flat roofs increases, the range of snow erosion and deposition decrease. When the threshold friction velocity is less than or equal to 0.15 m/s and the roof span is greater than or equal to 60 m, the deposition of snow drifting starts to appear in front of the leeward parapet. With further increase in roof span, roof snow drifting in the same direction as incoming wind becomes predominant, leading to increased snow deposition in front of the leeward parapet, which in turn results in a more uneven snow distribution on the roof.