Numerical simulation study of the effect of buildings and complex terrain on the low-level winds at an airport in typhoon situation

Apart from terrain-induced airflow disturbances and thunderstorms, buildings and artificial structures at airports may bring about sudden wind changes to aircraft in certain weather conditions. In the typhoon situation in the morning of 22 August 2008 under a generally crosswind situation, two aircraft landing at the Hong Kong International Airport reported encountering significant wind changes, which were considered to affect the operation of the aircraft. At the same time, a wind speed difference in the order of 10-15 knots was observed between the anemometers at the north and the south parallel runways of the airport. The cause of the wind changes experienced by the aircraft is studied in this paper by using numerical simulation, namely, using mesoscale meteorological models to provide the background wind fields, and nesting them with a computational fluid dynamics (CFD) model to study the effect of buildings and terrain on the airflow along the glide path of the landing aircraft. It is found that the complete set of simulation (i.e. including both buildings and terrain) successfully captures the wind speed difference between the north and the south runways, and gives the drop of the crosswind along the glide path exceeding the 7-knot criterion as adopted for building-induced wind changes affecting the normal operation of the aircraft. The results of the present study suggest that, for the timely warning of wind changes to be encountered by the landing aircraft, it may be necessary to consider examining the low-level wind effects of the buildings on the airfield by performing numerical simulations by mesoscale meteorological models as nested with a CFD model.