Research Progress of Air Lubrication Drag Reduction Technology for Ships

Air lubrication is a promising drag reduction technology for ships because it is considered to reduce the skin-friction resistance of ships by changing the energy of turbulent boundary layers. Air lubrication drag reduction can be classified into: microbubble drag reduction (injection of microbubbles along the hull), air film drag reduction (using a larger film of air to cover the ship bottom), and air cavity drag reduction (recesses underneath the hull are filled with air). In this paper, the research progress of the air lubrication drag reduction technology is reviewed from experimental and numerical aspects. For these three drag reduction methods, based on the aspect of experimental research, the main research focus is the analysis and evaluation of the influencing factors such as the gas injection form and drag reduction rate; in terms of theoretical research, the accuracy of the simulation calculation depends on the selection of the theoretical calculation model and the analysis of the drag reduction mechanism. The paper introduces, in detail, the typical experimental phenomena and the theoretical results of a numerical study of three types of drag reduction methods, revealing the essence of air lubrication technology to achieve drag reduction by changing the physical properties of the turbulent boundary layer.