Investigation of influence of compact actuators on air cavity in water flow under recessed hull

Abstract

Air cavity drag reduction is one promising method for reducing power consumption of ships. Its current practical applications are rather limited, owing largely to the fact that air cavity size and shape change drastically in response to variations in ship attitude, motions and speed, as well as sea conditions. This study explores how deployment of moveable hydrodynamic actuators near the air cavity on a small-scale simplified hull form can effectively increase the air cavity size in adverse hull positions. Experimentally investigated actuators included an adjustable plate in the front part of an air cavity, a stern spoiler, and a hydrofoil with regulated attack angle and streamwise position beneath the hull. In the cases of significant hull trims that are challenging for maintenance of long air cavities, optimal actuator placement increased cavity length by nearly 110% from its degraded state at negative trim and by 24% at positive trim. Actuator effects were more pronounced at higher water speeds.