Situated at the northern end of the mountainous Lantau Island, Hong Kong International Airport (HKIA) often experiences terrain-induced flow disturbances, such as windshear and turbulence. Aircraft passing through these highly disrupted airflows can experience changes in headwind and thus lift. Alternating losses and gains in headwind due to rapid fluctuations in wind flow pattern along the glide path could be hazardous to aircraft, particularly during landing. This thesis presents numerical simulations of these complex flow features, with the prevailing wind coming from the south, southeast and east. The simulations were carried out using high-resolution terrain data and mesh, with a horizontal resolution of 12.5 m at the bottom boundary and a first cell height of 8 m. Both Reyno...[ Read more ]

Situated at the northern end of the mountainous Lantau Island, Hong Kong International Airport (HKIA) often experiences terrain-induced flow disturbances, such as windshear and turbulence. Aircraft passing through these highly disrupted airflows can experience changes in headwind and thus lift. Alternating losses and gains in headwind due to rapid fluctuations in wind flow pattern along the glide path could be hazardous to aircraft, particularly during landing. This thesis presents numerical simulations of these complex flow features, with the prevailing wind coming from the south, southeast and east. The simulations were carried out using high-resolution terrain data and mesh, with a horizontal resolution of 12.5 m at the bottom boundary and a first cell height of 8 m. Both Reynolds Averaged Navier-Stokes(RANS) simulation and Large Eddy Simulation(LES) were used. The background wind profile was assumed to be logarithmic in a neutrally stratified boundary layer. To replicate one of the worst case scenarios for flow disturbances, it was decided that conditions corresponding to the passage of a tropical cyclone would be simulated, with a speed between the No.3 and No.8 signals, measured at the standard reference height. The generation and propagation of flow disturbances associated with high-speed airstreams emerging from the mountain gaps and valleys were visualized. Headwind Index(HI) and Crosswind Index(CI) were defined to analyze the transient nature of the terrain-induced flow disturbances along the glide paths on descending aircraft. Results show that windshear is most likely to occur at two critical places: (i) the eastern part of the south runway for a southerly wind and (ii) the western part of south and north runways for a southeasterly wind. By contrast, windshear is rarely expected to occur along the glide path of the proposed 3rd runway for all three background wind conditions considered in this study.