# A Review of Advanced Air Lubrication Strategies for Resistance Reduction in the Naval Sector
## 3 Numerical Studies
### CFD Simulations on ACDR
The study finds that while air cavities can reduce drag effectively, they also have a complex impact on heeling stability, making the management of heel angles critical for operational safety. The document concludes that while air cavity technology can substantially reduce drag, thereby improving fuel efficiency and reducing operational costs, it requires careful management of ventilation rates and heel angles to maintain heeling stability. The trade-offs between drag reduction and stability are highlighted as areas for further research and development in marine vessel design. [PERSON] et al. [65] focus on evaluating the bottom shape of a multi-stepped air cavity planing hull. The study includes both experimental and numerical investigations, varying velocity and air flow rate under the hull. Key areas of analysis include the influence of the Froude number on the air cushion shape and an observation of quantities like the frictional component of drag and air flow path lines, which are difficult to assess through traditional experimental tests. The turbulence model used in their CFD simulations is the SST k-\(\omega\). [PERSON] et al. [66] evaluate the performance of a planing yacht with air cavity using the LES model. The first part of the study assesses the drag curves of the hull without air injection using CFD; meanwhile, the second part investigates the injection of air under the hull. The study includes a comparison between experimental and CFD results. It offers an analysis of the streamlines and air distribution, as well as an assessment of the wetted and ventilated areas of the hull. This evaluation helps in understanding the relationship between the flow rate, the velocity of the hull, and the distribution of air. The findings from this research are instrumental in modifying the hull geometry to better accommodate the air layer. In additional, [PERSON] et al. [67] explored artificial cavitation by introducing air under a vessel to reduce drag. The study examined the complex interplay between cavitation and ship propulsion, offering a comprehensive model and parametric study to maximize efficiency. It concluded that while artificial cavitation significantly reduces drag, the actual benefits are influenced by complex interactions between the cavitation and the ship's propulsion system. The study highlighted the necessity of a nuanced understanding of these interactions to fully leverage cavitation for drag reduction. [PERSON] et al. [68] reported that the air cavity formed under a stepped planing hull significantly reduced the wetted area of the hull, thereby decreasing resistance and enhancing performance. The CFD simulations used in their study provided insights into the mechanisms through which air cavities influence hydrodynamics, suggesting directions for future hull design optimizations. [PERSON] [69] found that the interaction between the ship bottom air cavities and boundary layers could lead to optimized drag reduction if properly managed. The study emphasized the importance of understanding these interactions to predict and control the air demand for ventilated cavities effectively, which is crucial for achieving the desired reductions in resistance and enhancing overall ship efficiency.