Effects of bow geometry on bubble generation and transport around a research vessel

This study investigates how different bow geometries affect bubble generation and transport, a critical factor in sonar performance degradation due to bubble sweep-down. A coupled Eulerian–Lagrangian numerical framework with improved delayed detached eddy simulation method was developed. A staged numerical approach was adopted, combining the volume of fluid–Lagrangian multiphase model transition model for bubble generation under waves with a pre-seeded particle method for transport analysis in calm water. Results reveal that the intensity of bow–wave interaction is the decisive factor governing bubble generation. Model B, featuring a bow bulb, produced the highest bubble count due to intense impact at the bulb forefront and subsequent cavity collapse entrainment. In contrast, the axe-bow design of model A exhibited superior wave-piercing capability, resulting in minimal bubble generation. Regarding transport pathways, the wake flow and vortex structures dictated by the bow geometry are of paramount importance. For model B, the downward flow deflection induced by the bulb, combined with a discrete and low-strength bilge vortex, led to chaotic bubble sweep-down near the bow and widespread dispersion across the vessel's bottom. Conversely, model C, incorporating a flow guide channel and a robust, coherent bilge vortex structure, effectively confined the bubbles within the bilge flow field, thereby significantly suppressing their invasion into the critical flat bottom region. This research elucidates the underlying physics of how bow geometry affects bubble sweep-down, providing a theoretical foundation and a robust numerical tool for the optimal design of ship bows with low bubble sweep-down and enhanced acoustic stealth characteristics.