Hydrodynamic and oxygen transfer characteristics of a vertical round tube jet under regular waves with initial dissolved oxygen stratification

Dissolved oxygen (DO) concentration is an important parameter for marine water quality. Under natural conditions, DO concentration in seawater is usually vertically stratified with high value in upper layer and low value in bottom layer, which deserves a further examination. To alleviate the hypoxia problem in the bottom, a vertical round tube jet with high DO concentration was proposed under regular waves, and a series of experiments and a numerical model coupling CFD and DO transfer were conducted to investigate the hydrodynamic and oxygen transfer characteristics with initial DO concentration stratification. The results show that with the individual increases of wave height and period, or the decrease of still water depth, the dimensionless time-averaged vertical velocity at jet axis decreases, while the dimensionless half jet-width increases. With the increase of distance from nozzle, the dimensionless time-averaged vertical velocity at jet axis decreases and the dimensionless half jet-width increases. Oxygen transfer coefficient increases with the increase of the relative wave height and non-dimensional parameter. In addition, a series of wave and jet parameters were utilized to conduct a prediction equation for oxygen transfer coefficient, and the predicting deviations for 81.25% and 93.75% testing data were within +10% and +20%, respectively.