Microbubbles drag reduction characteristics of underwater vehicle during pitching movement.

In this study, we investigate the effects of ventilation parameters and motion characteristics on the drag reduction characteristics of microbubbles during the pitching motion of underwater vehicle. Based on the Population Balance Model (PBM), a numerical method is established that takes into account the phenomenon of microbubbles aggregation and breakage. The effects of the pitching frequency and ventilation volume coefficient on drag and lift are conducted in this study. The results show that the numerical method can accurately predict the distribution and force characteristics of microbubbles for the vehicle in pitching motion. Added mass force of the water phase is weakened when the vehicle is surrounded by microbubbles during the pitching motion. This causes a gradual decrease in the phase difference between the drag and lift coefficients under different pitching frequencies. Moreover, the drag rate of the microbubble is inversely related to the pitch angle. Namely, the drag reduction rate of microbubbles decreases with an increase in pitch angle. The drag coefficient decreases significantly when the vehicle is covered by the microbubbles. This leads to the phase of the drag coefficient slightly lagging behind the pitch angle. Furthermore, the lift coefficients of vehicle are similar for different ventilation flow rates. • The drag and lift coefficients' amplitudes and the phase difference increase with a higher pitching frequency. • The ventilation microbubbles have a significant drag reduction effect on the underwater vehicle with unsteady motion. • The effect of the ventilation volume coefficient on the lift coefficients is minimal. • The introduced microbubbles achieve drag reduction and provide essential normal force for the underwater navigation. [ABSTRACT FROM AUTHOR]