Research On Downburst Wind Field And Its Wind Loads To High-rise Buildings Considering Rough Topography

Downburst is a partial regional convective storm,the radial velocity is harmful to the near surface structure,so it is be included in the structural wind engineering field at very early time.In China,there are many study considering the influence of terrain factors on the wind field and wind load as well as the impact of the storm on various types of buildings and plants,but there has few studies considering the impact of different roughness topography on the wind field of downburst.In this paper,we stud y the characteristics of the wind field under different roughness topography,and on this basis,we further study the characteristics of wind load on the surface of the high-rise buildings within different roughness topography:(1)Based on the physical wind tunnel test and the numerical simulation method based on the explicit modeling of roughness,the effect of roughness on the wind field is studied.It is found that the radial distance and roughness have a very important effect on the flow attenuation.In the center of the storm,the intensity of the outflow is great,and the wind field is less affected by roughness.With the increase of the radial distance,or the greater the roughness,the more obvious the air flow attenuation,the lower the radial wind speed.Because downburst is a partial regional convective storm,the scale range is smaller,so the wind field is less vulnerable to the geomorphic characteristics,the impact of the scale characteristics of the wind field is greater.The absolute value of the extreme wind speed decreases,the position of the peak wind speed increases,and the roughness has a lifting effect on the wind profile.By comparing the transient characteristics,it is found tha t with the increase of roughness,the time of extreme wind speed will be advanced.(2)By comparing the transient development process of the cooling source model and the impinging jet model,the cooling source model and the impinging jet model are greatly different at the near surface zone.Because of the cooling source model considering the effect of gravity,the vertical wind field under jet region is more stable,the primary vortex of cooling source model is lower,the radial movement of primary vortex is more stable.The wind field of cold source model is more sensitive to roughness,and the difference of vertical wind profiles between different roughness landforms is larger than that of imping jet model.The cold source model uses compressible fluid and considers the coupling of temperature and density.It involves many complex physical processes such as viscous flow and heat conduction,so the energy loss is greater.(3)Based on the physical wind tunnel test and the numerical simulation method based on the explicit modeling of roughness,the effect of roughness on the wind pressure on the surface of high rise buildings in the wind field is studied.It is found that different roughness topography has an influence on the wind pressure on the building surface,but the effect is relatively small.The mean wind pressure coefficient(Mean Cp)results show that: With the increase of roughness,the windward wind pressure coefficient increases slightly,and the absolute value of leeward wind pressure decreases,the effect of roughness on the lateral wind pressure coefficient is not obvious.The RMS wind pressure coefficient(RMS Cp)results show that: with the increase of roughness,the fluctuating wind pressure coefficient increases with the increase of roughness,but the fluctuating wind pressure coefficient on the windward and leeward side is not obvious.Consistent with the wind field,the position of the e xtreme wind pressure coefficient increases with the increase of the roughness.