EXPERIMENTAL ANALYSIS OF BULBOUS BOW OPTIMIZATION FOR RESISTANCE REDUCTION IN SMALL SHIPS

Abstract

The bulbous bow is one of the most commonly used hydrodynamic applications for wave- making resistance reduction and fuel saving in ships. However, it is remarkably sensitive to geometrical configuration, wherein poorly designed arrangements can result in an increase in resistance rather than a reduction. Though a substantial amount of work has been accomplished on bulbous bows for bigger ships, smaller ships are surprisingly unrepresented in available literature despite having a higher sensitivity level for geometrical variations. In this research, this issue is examined in a systematic experiment to compare five bulbous bow designs with a baseline ship hull. A special facility with repetitive hydrodynamic forces was used to test unsteady flow phenomena around each bow shape. The hydrodynamic force index was normalised in a way to indicate flow stability, calculated based on unsteady pressure forces in the stagnation part of each bow, with smaller values of this index showing stable flow conditions when closely attached to the bow, while large values characterise flow separation, irregular waves, and high hydrodynamic instability. Results show significant performance variation among the tested designs. The best configuration exhibited very low hydrodynamic force index values of 3 - 4, reflecting good stability of flow, whereas values up to 8 - 9 were reached for less performing designs and the baseline hull, indicating high flow separation. These results confirm the strong dependence that exists between hydrodynamic stability and bulb geometry. This paper presents an experimental basis that underpins bulbous bow optimization in small ships and gives further backing to the development of geometry-driven design guidelines going beyond purely numerical approaches.