Numerical Simulation Of Downburst Wind Load

Downburst is a devastating strong wind appearing in thunderstorms, and its windprofile is quite different from those of atmospheric boundary layer wind. The windspeed of downburst increases rapidly with height at first and then increases rapidly,while the wind speed of atmospheric boundary layer wind always keep increasing withheight in height of gradient wind. Recent years, disasters caused by downburstprompted civil engineers to rethink the inadequate of doing wind field structural designwith traditional style of the atmospheric boundary layer wind. But the researches onwind load caused by downburst are rare so far, among which the study of a singlebuilding is the most. The former research didn’t examine the impact of the changes inbuilding height、cross-sectional shape and other factors, which will result in impact onpressure distribution and wind load characteristics. In order to study wind loadcharacteristics of downburst systematically, providing a reference for engineeringdesign, this paper did a list of numerical simulations on flow around buildings indownburst. After those simulations, the laws of wind load distribution andcharacteristics of on buildings were obtained. These laws are compared with those ofatmospheric boundary layer wind.In order to ensure the reliability of the numerical calculations, the analysis ofcomputation accuracy and grid patience are taken at first in this thesis. After the suitablenumerical model and grid size are found, the study of what kind of changes will becaught on pressure distribution with different aspect ratio is taken. At last, numericalsimulations of atmospheric boundary layer wind and downburst are taken respectivelywith two kind of building sections, four kind of building height. The main conclusionsare as follows:1. The position at which the largest wind pressure appears in downburst is low,about70m height, and wind pressure rises rapidly at fast, as well as decline. it isnoteworthy that the impact on200m high-rise buildings is significant;2. The wind load at each layer caused by downburst isn’t always increases withheight. The maximum wind load is probably appears at the position of70m high,followed by a downward trend, which is consistent with the wind profile characteristicsof downburst;3. In aspect of wind load, these caused by downburst is greater than those of atmospheric boundary layer wind in all numerical simulations. For low-rise buildings,the situation in downburst is worse. With the increase in the height of the building, thewind loads caused by atmospheric boundary layer wind is reaching those of downburst;4. In aspect of basal moment, these caused by downburst is greater than those ofatmospheric boundary layer wind, except for the200m high circular building. Also, thesituation in downburst is worse for low-rise buildings.