Numerical study on the influence of air layer for propeller performance of large ships

Based on the RANS equation and the VOF two-phase flow model, numerical simulations were conducted about the air layer on the lower surface of a large ship model with and without propeller. The influence of air injection on the propulsion performance of the propeller is investigated by comparing of thrust and torque of propeller. Numerical results indicate that the air does not enter the propeller working area directly for the design bottom cavity in this paper. The average of the axial speed at the propeller disk surface would increase and the average wake fraction decrease with air injection. Under the same inflow velocity and rotation of the propeller, the bottom air injection would make the propeller thrust and torque become smaller, so the K-T and K-Q decrease. The air injection reduces the resistance of the ship model and the ship's self-propelled point would change. Therefore, the studies of the effect of the air injection on the propeller propulsion performance require to be analyzed at the new self-propelled point.