Impact of buildings on the low level airflow at the airport – example of hangars

Apart from terrain-induced airflow disturbances and thunderstorms, buildings and artificial structures at the airport may bring about sudden wind changes to the aircraft in certain weather conditions. In the typhoon situation in the morning of 22 August 2008, 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, wind speed difference in the order of 10 – 15 knots was observed between the anemometers at the north and the south 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. Three separate CFD simulations are performed, namely, with the presence of both the buildings and the terrain, having the buildings only, and having the terrain only. 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 a drop of crosswind exceeding 7-knot (the criterion as adopted for building-induced wind changes affecting the normal operation of the aircraft) along the glide path. Moreover, the buildings are found to be the major contributor to the crosswind change as experienced by 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 would 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.