The Numerical Simulations Of Thunderstorm Downbursts And Its Effect On Low-Flat Structures

Thunderstorm downbursts is attributed to extreme wind. Due to its high intensity, short duration and wind velocity profiles different significantly from boundary layer profiles, thunderstorm downbursts has severally damaged many buildings such as long-span structures and transmission towers. Therefore, it has been a critical issue for wind resistance design.Using the state art of CFD, the study on wind field characteristics of thunderstorm downbursts and its affect on Low-Flat roof were deeply conducted. Considering many factors, intensity,diameter,height of impinging,Reynolds ,etc, horizontal and vertical wind velocity profiles along height(Z) and horizontal distances(r) were approached. On the basis of 2-D simulation, geomorphologic and inclined angle of impinging jet were taken into account in 3-D simulation. In addition, using 2-D and 3-D simulation results, the empirical models for horizontal and vertical wind velocity profiles were established, and compared with existing CFD simulation and scaled test results.In unsteady wind filed characteristic, considering thunderstorm translation and utilizing dynamic mesh of FLUENT to simulate dynamic flow field, horizontal wind velocity profiles from different times and locations were attained. By settting monitoring points in flow filed, wind velocity time-history curves at different points were obtained. Furthermore, wind velocity time-history curves were also gained using Velocity-Compose-Model. It is demonstrated results of two methods show good agreement with field measurement results.In addition, in aspect of downbursts effects on Low-Flat roof, it is calculated that the distribution of the wind pressure coefficient on roof under horizontal and vertical wind loads of downbursts using full-scale model. According to the theory of boundary layer wind tunnel, wind pressure height coefficient of downbursts and local shape coefficient of Low-Flat roof were approached, which supplies some suggestion to designers on resistance to thunderstorm downbursts.