Study On The Characteristics Of Wind Field Over Mountain Pass Topography By LES

Mountain pass is a typical topography of complex mountain areas.When wind flow over mountain pass terrain,there are many complex flow phenomena,including the canyon wind,cross-mountain wind and backflow impact.The complex flow is easy to induce difficulties in the prediction of wind speed around mountain pass terrain.For wind resistant design of buildings and bridges in mountainous areas and the utilization of wind energy,it is of great significance to investigate the wind field characteristics around the mountain pass terrain.In this paper,the spatial-averaged large eddy simulation(LES)method was used to study the wind field characteristics of mountain pass landform under different parameters.The corresponding mechanism of the flow field was analyzed.The main contents of this paper are as follows:(1)The numerical simulation method and parameter settings were verified by comparing the LES calculation results of independent mountains with the corresponding wind tunnel test data.The wind field characteristics of typical mountain pass landform were compared and analyzed in detail.The influence mechanism was discussed with combination of the simulated flow field.Affected by the upstream slope in front of the pass and the mountains on both sides,the backflow phenomena were observed,as well as the standing vortex produced by the accumulated energy.There exists relatively strong impacting phenomenon on the leeward sides when flow around the mountains,inducing obvious vortex shedding.Multiscale vortices gradually appear around the mountain pass,resulting in relatively concentrated energy.The above phenomena are the main reason for the relatively large value of the averaged and fluctuating wind speed at the entrances of both the mountaintop and the valley of the mountain pass.(2)Taking an actual mountain pass as the object,the most unfavorable wind direction was firstly determined by stead-state numerical simulation under different wind directions,based on the Reynolds averaged turbulence model.Large eddy simulation of flow around the actual mountain pass was then carried out for the most unfavorable wind direction.Characteristics of wind filed of the actual mountain pass were analyzed for the simulated results by LES,in the aspect of the wind profiles and variation of the flow field.Larger mean wind speed is observed at the higher side mountaintop.The mean wind speed is relatively small at the entrance of the valley.As for the impact of the wind field of the mountain pass,the influence of mountain crossing wind is greater than that of Canyon wind.(3)According to the main topographic characteristics of the actual mountain pass,a simplified model of the mountain pass was established.Unsteady flow around the simplified mountain pass was simulated by LES at the most unfavorable wind direction,determined by the steady-state RANS calculation.By comparing the simulated wind field results with those of the above actual mountain pass,the simplified model was found to be capable of reflecting the wind field characteristics around the actual mountain.Numerical simulations were then performed on the simplified model with different elevation and length of the mountains.Corresponding effects on the averaged and fluctuating wind profiles,the terrain correction coefficient,and the flow field are analyzed.Based on the proposed expression of mountain pass topographic correction coefficient and the present parametric analysis results,the modified topographic correction formula of mountain pass with different parameters is presented.