Numerical simulations of bubble formation and acoustic characteristics from a submerged orifice: The effects of nozzle wall configurations.

The detachment of bubbles from an underwater nozzle inevitably generates distinct acoustic signals. This work proposes numerical simulation models to investigate the effect of different nozzle wall configurations on bubble formation and acoustic characteristics. A combination of large eddy simulation (LES) model and Ffowcs Williams–Hawkings (FW-H) equation is successfully applied to predict bubble acoustic pressures. The adaptive filtering techniques of signal processing are utilized in bubble acoustic analyses. In particular, transient spectrum based on time–frequency analyses can not only precisely count the bubbling period but also effectively measure the bubble sizes. The numerical results for bubble size are in good agreement with the theoretical data (less than 10% deviation). The main results of this research show that the structure of the nozzle wall plays a guiding role in vortex motion around bubbles. The bubble size also increases with the increase in exit-lip thickness, whereas the bubbling rate decreases. [ABSTRACT FROM AUTHOR]