Research On Wind Pressure Distribution Of Single-column Billboards Under The Thunderstorm Downburst

With the aggravation of climate change and global warming,the downburst as the representative of strong convective weather gradually increased.The downburst is developed by the exchange of cold and warm air in thunderstorm that generate the strong sinking airflow slammed into the ground.The special wind profile keep on bringing damage to the structures such as billboards and transmission towers,which has caused serious impacts.The current load code in China lack effective guidance for the extreme weather such as downburst.This paper attempts to adopt numerical simulation CFD methods to investigate the billboard structure wind pressure character under the thunderstorm downburst,and the effects of radial position and wind direction of the downburst on wind pressure characteristics of billboard have been studied.The main contents of this thesis include as follows:(1)The wind pressure coefficient distribution on single-column-supported two-plate billboard in different radial position and wind directions were investigated.The paper mainly study the influence of radial position and wind directions on pressure coefficients of plate,and analyze the flow characteristics around the billboard in different wind directions.The results show that all surfaces of the model are subjected to greater positive pressure at R=0Djet,the wind pressure coefficient on the windward surfaces gradually decrease with the radial distance increase,and the strength of the rear vortex on the back side gradually decrease.The distribution of the wind pressure coefficient on the surface changes significantly as the wind direction change,the peak wind pressure coefficient gradually decrease,and the wind pressure coefficient around this area becomes no longer full.Meanwhile,the wind pressure coefficient distribution on the windward surface changes from symmetrical to asymmetrical,and reach the peak on the side near the wind field,then decrease along the side far from the wind field.The resistance to the incoming flow gradually decrease as the wind direction increase,and the vortex behind the back side disappear.In the upper part of the back side surface of the model,the flow separates at the front edge then attaches at the rear end.(2)The wind pressure coefficient distribution on single-column-supported three-plate billboard in different radial position and wind directions were investigated.The results show that all surfaces of the model are subjected to greater positive pressure at R=0Djet,and reach the peak at R=1Djet,then gradually decrease with the radial distance increase.At α=0°,the flow separates at the windward edge then generate vortex in the hollow area of the billboard,the flow mainly produce suction at the inside surfaces of the model.At α=30°,the flow vertically hits the windward surface of the billboard,and the windward surface is subjected to greater positive pressure.Considering thewind pressure superposition of rear surface,the maximum total wind pressure coefficient changes from 1.53 to 1.60.(3)The wind pressure coefficient distribution on single-column-supported four-plate billboard in different radial position and wind directions were investigated.The results show that the wind pressure distribution on the windward surface is basically the same as the two-plate billboard.As the radial distance increase,the wind pressure coefficient gradually decreases.The flow separates at the windward edge and then produce suction at the side surfaces.As the wind direction continues to increase,the area where the flow vertically impacts becomes no longer full.In the inside of windward,the suction near the wind field gradually increases,and the maximum total wind pressure coefficient moves to the side near the wind field.The vortex formed in the hollow area of the billboard and then attaches at the back surfaces.