Experimental investigation on the characteristics of pressure oscillations for sonic steam-air jet in subcooled water

•Back-attack phenomenon would occur in steam-air jet experiments.•The pressure oscillation frequency increases initially and then decreases with the increase of air mass fraction when the water temperature is 80 ℃.•An empirical equation for predicting the radius of the steam bubble separated from the end of the pure steam plume is proposed.•The prediction equation for the oscillation frequency of steam-air jets is proposed based on bubble oscillation theory. To investigate the characteristics of pressure oscillations for sonic steam-air jets in subcooled water, a series of experiments are conducted, and pressure oscillations are recorded and analyzed. The results indicate the occurrence of the back-attack phenomenon for steam-air jets. The back-attack phenomenon is the result of the necking of the steam-air plume, which hinders the flow of gas downstream, thereby causing some gas to expand in the opposite direction and back attack the nozzle. When the back-attack phenomenon occurs, a pressure pulse occurs at the nozzle outlet simultaneously. Regarding jet pressure oscillation, the intensity of pressure oscillation increases with the increase of temperature and air mass fraction. The dominant frequency of pressure oscillation decreases with the increase of water temperature and air mass fraction when the water temperature is lower than 80 °C. The pressure oscillation frequency increases initially and then decreases with the increase of air mass fraction when the water temperature is 80 °C. An empirical equation for predicting the radius of the steam bubble separated from the end of the pure steam plume is proposed, and the deviation is within the error band of ±15%. In addition, a prediction equation for the oscillation frequency of steam-air jets is proposed based on bubble oscillation theory, which can predict the dominant frequency when the air mass fraction is 0.01–0.5, the water temperature is 25–80 °C, and the inlet pressure is 0.3–0.7 MPa.