Numerical Simulation of Characteristics of Wind Field at Bridge Sites in Flat and Gorge Terrains under the Thunderstorm Downburst

To investigate the effects of thunderstorm downburst on the characteristics of wind field at bridge sites in flat and gorge terrains, firstly, numerical simulation of wind fields in the flat terrain under the thunderstorm downburst was conducted through the SST k-ω turbulence model, combined with the impinging jet technology. After verification of the reliability of the numerical model, settings, and methods, the characteristics of wind field over a long-span bridge site in a gorge terrain under the thunderstorm downburst were investigated and the distributions of wind speed and wind attack angle in the flat and gorge terrains were compared. The results show that, under the effects of the thunderstorm downburst, the wind speeds are relatively maximum at the midspan point of the girder in the flat terrain. Besides, the farther away from the midspan point, the smaller the wind speeds, which is opposite to the case in the gorge terrain. The wind speeds at each typical monitoring point are basically the same in the two terrains, before the thunderstorm downburst hits the bridge girder. Later the wind speeds at each point in the gorge terrain are much higher than those in the flat terrain. Most wind attack angles are negative at the monitoring points in the flat terrain, but the farther away they are from the midspan point, the greater the wind attack angles will be. However, the wind attack angles at the monitoring points in the gorge terrain are generally larger than those in the flat terrain, and they gradually turn to be positive farther away from the midspan point. In the flat terrain, both wind speeds and wind attack angles (or their absolute values) at the girder are large within about t = 75∼130 s, indicating that the thunderstorm downburst may exert significant effects on the bridge. However, in the gorge terrain, due to the large wind speeds and wind attack angles (or their absolute values) at the girder after t = 75 s, full attention needs to be paid to the effects of the thunderstorm downburst during this period.