Acoustics of a liquid jet impinging on a solid surface
course project - JNCASR
Introduction
It is a common observation that a liquid jet emerging from an ori ce and impacting a solid surface has a distinct acoustic signature. In this study the mechanisms for this sound production were investigated experimentally.
Experimental setup
The setup mainly involved an apparatus to produce the liquid jet and measurement tools to study the flow structures and sounds including a high speed camera and condenser microphone. The jet was maintained at a given flow rate using a constant head tank and was made to impinge on a heavy glass plate. Care was taken in draining the liquid from the glass plate so as to avoid any secondary sounds which may contaminate the acoustics data. To study how the flow structures of the jet before and after impingement affect the acoustics we added a simple mechanism to precisely align the video and audio frames. Two sets of images were collected: one of the jet before impingement and a second of the underside of the glass plate on which the jet impinges. The videos were shot at 3000 fps and the audio sample rate was 44100 Hz.
Results in brief
The audio tracks were Fourier transformed to yield the frequency spectrum of the sound. Also the envelope of the sound signal was plotted with respect to time. It was found that there were two distinct types of sound signatures. The first was a continuous "pitter-patter" type sound which resulted from the impact of the water droplets on the solid surface. The second was a clear sharp sound with discernible pitch which appeared seemingly at random. Beyond a certain separation between the nozzle and plate and a low enough flow rate the jet displays the classic Rayleigh-Plateau instability and breaks up into droplets. The separation between these droplets is found to be inversely proportional to the dominant frequency in the fi rst type of sound. The second type of sound was seen to have a positive correlation to bubbles formed in the liquid pool on the glass plate. This was shown by comparing the video and audio tracks and analyzing the sounds at the precise moment of bubble formation. Furthermore, comparison of the dominant frequencies of this second sound type was made with simple estimates from radial oscillations of a gas bubble in water and was found to compare very well. The amplitude of this sounds was also seen to be proportional to the number of bubbles formed at that instant.
To know more about this work you can read the report: Experimental investigation of the acoustics of a liquid jet impinging on a solid surface
It is a common observation that a liquid jet emerging from an ori ce and impacting a solid surface has a distinct acoustic signature. In this study the mechanisms for this sound production were investigated experimentally.
Experimental setup
The setup mainly involved an apparatus to produce the liquid jet and measurement tools to study the flow structures and sounds including a high speed camera and condenser microphone. The jet was maintained at a given flow rate using a constant head tank and was made to impinge on a heavy glass plate. Care was taken in draining the liquid from the glass plate so as to avoid any secondary sounds which may contaminate the acoustics data. To study how the flow structures of the jet before and after impingement affect the acoustics we added a simple mechanism to precisely align the video and audio frames. Two sets of images were collected: one of the jet before impingement and a second of the underside of the glass plate on which the jet impinges. The videos were shot at 3000 fps and the audio sample rate was 44100 Hz.
Results in brief
The audio tracks were Fourier transformed to yield the frequency spectrum of the sound. Also the envelope of the sound signal was plotted with respect to time. It was found that there were two distinct types of sound signatures. The first was a continuous "pitter-patter" type sound which resulted from the impact of the water droplets on the solid surface. The second was a clear sharp sound with discernible pitch which appeared seemingly at random. Beyond a certain separation between the nozzle and plate and a low enough flow rate the jet displays the classic Rayleigh-Plateau instability and breaks up into droplets. The separation between these droplets is found to be inversely proportional to the dominant frequency in the fi rst type of sound. The second type of sound was seen to have a positive correlation to bubbles formed in the liquid pool on the glass plate. This was shown by comparing the video and audio tracks and analyzing the sounds at the precise moment of bubble formation. Furthermore, comparison of the dominant frequencies of this second sound type was made with simple estimates from radial oscillations of a gas bubble in water and was found to compare very well. The amplitude of this sounds was also seen to be proportional to the number of bubbles formed at that instant.
To know more about this work you can read the report: Experimental investigation of the acoustics of a liquid jet impinging on a solid surface
