ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pAO1. Effects of salinity on the acoustics of bubble plumes.

Gregory J. Orris

Michael Nicholas

Naval Res. Lab., Washington, DC 20375

A previous paper [ 2826(A) (1993)] presented acoustic data collected near bubble plumes of various void fractions and sizes produced by varying the flow velocity of a water jet impinging normally on a water surface. Subsequent analysis has revealed that the data's spectral content varies considerably between the two phases of the experiment---one involving fresh water in Lake Washington and the other involving salt water in Puget Sound. In the fresh-water portion of the experiment the spectra are completely dominated by modes corresponding roughly to the gross dimensions of the plume. In the salt-water portion of the experiment, the salts and other contaminants (which act as surfactants and lower the surface tension) dramatically reduce the mean bubble size with respect to that of fresh water. The acoustic data from the salt-water experiment are drastically different from that of the fresh water, and show little or no modal structure. For this particular physical situation it is suggested that the dominant acoustic generation process is likely to be turbulence. Furthermore, differences in the acoustic signatures of the experiment could be exploited to determine, amongst other things, the concentration of the salts and contaminants.