Experimental investigation of the cavitation control in a convergent–divergent nozzle using air injection

Detailed investigation of cavitation dynamics in a converging–diverging nozzle using air injection at different injection positions is carried out. Air is injected at upstream and downstream points of the nozzle to evaluate its influence on cavitation phenomena, as reported for the first time. The water and air flow rates varied from 3000 to 6000 Liter per hour (LPH) and 5–10 LPH, respectively. Cavitation phenomena are captured by high-speed cameras at different stages of cavitation, including sheet and cloud. Particular attention is given to estimate cavitation length, cavity area, and energy distribution by image processing. Very distinct frequencies are identified for different air injection flow rates and their locations, reflecting a strong correlation between cavity dynamics and air injection. Additionally, continuous Morlet wavelet transform is applied to the data, which suggests the coexistence of bubbles with multiple frequencies at any given instance; their amplitude is very notable with time. Altering the injection points results in varying bubble lengths and distributions along the channel, highlighting the crucial role of injection location in optimizing cavitation efficiency. These findings offer valuable insights into the mechanisms governing cavitation control.