Aerodynamic sound generation induced by flow over small, cylindrical cavities

An experimental investigation has been conducted on the production of high intensity tones by small cylindrical cavities in a flat surface. The application of such a mechanism is to the acoustic coding of moving objects containing drilled holes. The sound intensity and frequency have been determined as functions of flow velocity, diameter and depth of the cavities. As a practical matter, it is possible to produce a whistle producing 106 dB at 30.5 cm distance from a cylindrical hole of 0.5 cm diameter and 1.2 cm deep with an airflow of 60 m/s past the hole.