Large‐eddy simulations of neutrally stratified airflow over the complex terrain around Hong Kong International Airport with a three‐runway system

Situated just north of the mountainous Lantau Island, Hong Kong International Airport (HKIA) can experience terrain‐induced airflow disturbances under certain meteorological conditions, such as during a tropical cyclone. For approaching aircraft, such disturbances can lead to wind shear, jeopardizing flight safety. In this numerical study, large‐eddy simulations of turbulent airflow over Lantau Island are performed under neutrally stratified conditions with a view to understanding how terrain‐induced disturbances affect the headwind and crosswind experienced by aircraft landing at HKIA. Analysis of 1 min output data shows that, consistent with previous studies, high‐speed transient flow disturbances can emerge from gaps in the mountains of Lantau Island, producing spatiotemporal variations in wind speed and direction along the glide paths. An attempt is made to quantify the relative likelihood of wind shear by analysing how frequently wind‐speed fluctuations due to terrain interaction exceed predefined thresholds within a prescribed time window. The results show that wind shear is most likely to occur (1) on the eastern approach to the south runway (25L) in a southerly background wind; and (2) on the western approach to the south runway (07R) in a southeasterly background wind. These findings are consistent with the present operations at HKIA, where the north runway, which has a lower likelihood of wind shear, is used as the predominant landing runway. The simulations also show that the proposed third runway, which is currently under construction, will see an even lower likelihood of wind shear because it is the farthest of the three runways from Lantau Island. The study provides new insight into the unsteady flow behaviour at an airport surrounded by complex terrain, contributing to aviation safety. Hong Kong International Airport (HKIA) is known to be susceptible to terrain‐induced airflow disturbances arising from Lantau Island. For approaching aircraft, such disturbances can cause wind shear, jeopardizing flight safety. Here large‐eddy simulations show that high‐speed transient airflow disturbances can emerge from gaps in the mountains of Lantau Island, producing spatiotemporal variations in wind speed and direction along the glide paths of aircraft landing at HKIA. The study provides new insight into the unsteady flow at an airport surrounded by complex terrain, contributing to aviation safety.