Experimental and numerical investigation of air lubrication on a planing hull with Double Interceptor System

The present paper presents the study of the application of air lubrication system (ALS) on DIS (Double Interceptor System) equipped hull to improve its performances. It was observed that without ventilation, the low-pressure area behind the forward interceptor leads to excessive downforce, reducing trim and rise and increasing wetted surface with respect to the bare hull case. The air lubrication approach to improve the effectiveness of the DIS on a planing hull has been analyzed through natural and forced ventilation. The model has been tested for Fr between 0.97 and 1.46 (Fr ∇ between 0.67 and 0.94) and the air flow rate range was varied from 0 to 20.5 l/s. The ventilated DIS showed significant improvements compared to non-ventilated DIS due to mutual effects between reduced wetted surface, pressure distribution and running attitude compared to the bare hull, the natural ventilation configuration showed improvements in resistance at lower speeds, but not enough to achieve substantial performance gains for higher speeds. Investigating the hull resistance and running attitude at different airflow rates, two key regions were identified, one where drag exhibits a significant decrease with airflow and a second one where only marginal reduction in resistance is obtained with increasing airflow. • The DIS (Double Interceptor System) is applied to a planing hull to create a cavity with natural and forced ventilation. • The air lubrication technique consists in hull bottom ventilation using 8 pipes installed behind the forward interceptor. • The natural ventilation configuration showed some improvements in resistance at lower speeds, but it was not enough to achieve substantial performance gains for higher speeds where high forced air flow rates were necessary. • An increment above Q = 9.7 l/s in airflow results in only marginal reductions in resistance. This is consistent with the observation that trim and rise of CG remain almost constant for flow rates exceeding this value. • At low speeds, the air flow rate of Q = 9.7 l/s corresponds to the maximum resistance reduction compared with respect to the bare hull, while at high speeds, the maximum resistance reduction was achieved with the highest airflow. • It was found that the resistance obtained with CFD simulations systematically underestimates the experimental results at higher speeds and flow rates.