Study On Wind Field Characteristics Of Moving Downburst Over Flat And Sloping Terrain

Downburst is a short-term strong downdraft air impinging on the ground during the thunderstorm,with an extremely high velocity generated close to the surface and spread around.Downburst have high frequency and strong destructive,which has attracted widespread attention from domestic and foreign researchers.In recent years,field measurements,theoretical studies,wind tunnel tests,and numerical simulations have been applied to a series of studies on downburst storms.The existing researches are mainly directed at static downburst,but actual downburst is often accompanied by storm movement.The wind field characteristics are significantly different from those of stationary storms.Similar to the atmospheric boundary layer wind field,the topography also has a significant amplification effect on the downburst wind field.In order to further study on wind field characteristics and development laws of moving downbursts considering the influence of flat and sloping terrain and further improvement on the study of related wind profiles,as well as provide a reference basis for subsequent structural wind resistance design,both wind tunnel test and large eddy simulation are adopted to study the wind field characteristics of mobile downburst in this paper.The main contents include:?1?A movable impinging jet device is used in a wind tunnel laboratory to simulate the wind field characteristics of flat and sloping terrain in static and moving downburst.The results show that the nozzle diameter has little influence on the normalized impinging jet wind field.The nozzle movement speed has more obvious amplification effect on the peak value of the curve.The jet speed has little effect on the peak value.The position of the ravines with different gradients ha the acceleration effect on the wind speed.And the greater the slope is,the more pronounced the acceleration effect will be.?2?Large eddy simulate on method was used to simulate the three-dimensional scale of moving downburst,verifying the transient numerical simulation reliability.On this basis,a number of simulation conditions were added to study the wind field characteristics of moving downburst under flat terrain.The results show that the direction of the wind speed changes significantly after the mobile downburst impacts the ground,and the moving speed has a significant increase on the horizontal wind speed in front of the storm,while the wind speed behind the storm has a certain degree of reduction.The peak position of the curve is proportional to the ratio of 1:2:3 with the moving speed.The duration of the descending segment of the curve is inversely proportional to the moving speed,basically satisfying the ratio of 3:2:1.While the proportional relationship of the jet velocity is just on the contrary.The peak value of the wind speed time history is related to the eccentric distance.And the larger the offset distance is,the smaller the peak value will be.?3?Large eddy simulation was used to study the wind field characteristics of sloping terrain under moving downburst.The results show that the horizontal wind profile of the slope is in the range of-2D_jet²D_jet and the extreme wind speed can reach about 62m/s,which may cause serious damage to the horizontally distributed transmission tower line system and multi-span plant.So we should take full consideration.The wind speed of the slope reaches the maximum at the cornice and the magnitude of the positive and negative peaks differs by about 25%.The peak value of the wind speed time history curve is related to the slope and the eccentric distance.The larger the slope and the eccentric distance are,the smaller the peak at the same location is.