Formation Mechanism And Risk Assessment Of Low-level Wind Shear At Airports Under The Influence Of Terrain

Low-level wind shear at airports is the "invisible killer" of aircrafts during takeoff and landing stages,known as "the devil of aviation flight".Low-level wind shear caused by the mountain terrain has the characteristics of small spatial and temporal scale,high intensity,strong paroxysm,and great difficulty in early warning,which seriously threatens the safety of aircraft during take-off and landing and reduces the operational efficiency of airports.Mountainous terrain regions are widely distributed in China.With the continuous development of civil aviation power construction in China,especially the rapid development of many branch transport airports and general airports,more and more airports will be adversely affected by the low-level wind shear caused by surrounding terrains.Therefore,it is necessary to explore the formation mechanism of the low-level wind shear under the influence of terrains and evaluate its risk,to provide theoretical support for reducing the risk of low-level wind shear accidents caused by mountainous terrains.By means of the atmospheric boundary layer wind tunnel test and the numerical simulation of winds,the formation mechanism and risk range of low-level wind shear under the influence of typical mountain terrains were studied.Firstly,based on the investigation of the mountain terrains around the actual airports and relevant literature,four typical mountain terrain schemes were proposed,namely cosine-single-mountain,cosine-double-mountain,cosine-mountain-range,and cosine-canyon.Then,aiming at the influence of four typical mountain terrain on the wind field,the atmospheric boundary layer wind tunnel test was carried out,and the characteristics of the average wind field under the influence of typical mountain terrains were analyzed.Next,the reliability of the numerical simulation method used in the study was verified by the wind tunnel test results.On this basis,the numerical simulation experiments were carried out for 120 working conditions of 4 types of typical mountain terrains including5 kinds of mountain slopes and 6 kinds of mountain heights.Then,based on the wind field numerical simulation results,the formation mechanism of low-level wind shear under the influence of typical mountain terrains was analyzed,and the risk of low-level wind shear caused by typical mountain terrains was evaluated by using the crosswind shear assessment method based on virtual glide path detection.Finally,taking Hong Kong International Airport and Nyingchi Meilin Airport as practical cases,the risk of low-level wind shear under the influence of the surrounding terrain of the airport was examined based on the wind numerical simulation,and the numerical simulation results were verified based on the actual observation data of the airport.The results show that the wind numerical simulation method used in the study could effectively represent the average wind field characteristics under the influence of typical mountain terrains.Under the influence of cosine-single-mountain and cosinemountain-range,the v-shape variation of crosswind on the virtual glide path is the main cause of the low-level crosswind shear.Under the influence of cosine-double-mountain and cosine-canyon,the "W" shape change of crosswind on the virtual glide path is the main cause of low-level crosswind shear,and the increase of intermediate wind speed reflects the crossing effect between the middle of the double mountain and the middle of the canyon rather than the narrow tube effect.The method proposed in this paper could be effectively applied to the risk assessment of low-level wind shear in practical airports.In addition,the crosswind shear risk assessment method based on virtual glide path detection was adopted in this paper to obtain the crosswind shear risk range assessment tables under the influence of typical mountain terrains,and the impact of mountain height and slope changes on the risk range was analyzed.The results of this study contribute to the overall understanding of the low-level wind shear caused by mountain terrains.Besides,the results could provide references and theoretical supports for the risk avoidance strategy of the low-level wind shear at the airport planning,site selection and runway layout phases,and could improve the effectiveness of the layout of meteorological and wind field observation equipment at airports.Therefore,this study is expected to help in reducing the adverse risk of lowlevel wind shear caused by mountain terrains to the civil aviation safety and the airport operation,and it possesses important theoretical significance and great practical value to ensure the safety of aircrafts during take-off and landing and improve the operational efficiency of airports.