Wind blowing past a structure can sometimes result in auditable sounds. You have most likely heard a howling or whistling sound in the wind, or heard a thin plate “singing” in the wind. In the same way, you have most likely heard something rattling or banging against something.
This can cause discomfort to inhabitants or users of both buildings as well as on bridges or other structures. We refer to these sounds as wind-induced noise.
If the wind conditions resulting in noise occurs frequently it is necessary to find suitable mitigation measures. Wind tunnel testing on full-scale mock-up models is an effective tool for evaluating wind induced noise.
Wind induced noise may be generated in a number of ways. Field measurements and structural are often used to identify the most likely source of the sound.
A classic example is when one blows across the top of an empty bottle. This may cause resonance in the air in the cavity. The phenomenon is also know as Helmholtz resonance. The same principle is used in organ pipes, where it – intentionally – generates sounds at one fundamental frequency. Unfortunately, the same phenomenon may cause – unintended – sounds of a façade skin.
Wind blowing over small holes, sharp edges or extruded profiles may cause high (say >5kHz) whistling. Cables may generate aeolian tones like a wind harp.
Further, complicated interactions between vortices in the wind and structural frequencies may cause e.g. vibrations in plate-elements used for façade skin. This has been experiences in the 500-2000Hz band disturbing for human hearing.
Finally, loose structural components may cause rattling or banging.