Acoustic emission of water drops impacting on a heated surface

The sound generated by the impact of water drops on heated surfaces is studied experimentally, with the purpose to identify the sound features characteristic of the various impact morphologies. Whilst the sound of drops impacting on liquid surfaces has been investigated extensively, little attention was given to the sound of drops on solid, heated surfaces. The identification of sound features specific to different impact morphologies would enable the impact regime recognition without the need of high-speed imaging visual inspection, and can be used to train machine learning algorithms for automatic impact regime detection. Water drops were generated from a hypodermic needle suspended above a polished aluminium surface at temperatures between 100°C and 400°C, with impact Weber numbers ranging from 30 to 150. The sound generated upon impact was captured by a supercardioid condenser microphone, and compared with high-speed video recordings of the the impact. Results suggest different impact morphologies generate a sound with distinctive spectral features.