Parametric studies on bulbous bow to reduce the bow-induced vortices for a naval vessel

Abstract

The hydrodynamic optimization of a bulbous bow for naval vessels presents various challenges to the industries and scientific communities, considering aspects like reducing resistance and noise. In the context of sustainable shipping and current Energy Efficiency Design Index (EEDI) requirements, merchant vessels are seeking an optimized bulbous bow that offers improved resistance characteristics, thereby ensuring compliance with statutory emissions requirements. On the other hand, naval vessels, especially those equipped with sonar equipment in their bulbous bows (commonly known as sonar domes), often face issues related to noise which interfere with sonar operations, potentially affecting the vessel's stealth signature. Equally important but less discussed is the phenomenon of vortex shedding from the bow, where the shape of the bulbous bow leads to vortex shedding which interferes with the propeller. The bow-induced vortices can decrease propeller efficiency, induce premature cavitation, and increase propeller noise, which is a significant concern both stealth of the vessel and environmentally. In the current study, an ITTC benchmarking model was considered for resistance validation, which indicated a 1 % to 6 % deviation from experimental results for the viscous resistance component of the vessel. After validation, the analysis was carried out for variations in bulbous bows using the Free-Form Deformation (FFD) method using CAESES. A total of twenty-five variations of the bulbous bows were simulated at Froude number of 0.248 and 0.45 to study the effect of the bulb vortex on the propeller wake. This indicated that while the curvature and slope of the bulb at the top and bottom parts can control the strength of the bow vortex generated but may not significantly reduce the wake fraction of the vessel.

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*Corresponding author

Email address: sheejaj@imu.ac.in