Numerical Investigation of Flow Characteristics Around Rudder with Sacrificial Anodes

Çopuroğlu H. İ., Şener M. Z., Peşman E., Özmen Y.

Journal of naval architecture and marine technology, cilt.228, sa.1, ss.55-63, 2026 (TRDizin)

Özet

Cathodic protection is a method for protecting steel structures immersed in water from electrochemical corrosion. In the maritime industry, this protection is achieved by installing zinc or magnesium galvanic anodes on the hull and underwater components of ships, such as rudders, propellers, and shafts. Although sacrificial anodes effectively prevent corrosion, their presence may alter the flow characteristics around protected components. In this study, the effects of anode shape on the hydrodynamic characteristics of a rudder with a National Advisory Committee for Aeronautics 0018 cross-section were numerically investigated. Three cases were considered: a bare rudder without an anode, a rudder fitted with a rectangular (flat bar) anode, and a rudder fitted with a semi-elliptical (disc) anode. The volumes of both anodes were kept identical for a fair comparison of their hydrodynamic effects. All cases were analyzed at a Reynolds number of 15000 and rudder angles of attack of 0°, 10°, 20°, and 30°. Three-dimensional, time-dependent numerical simulations were performed using computational fluid dynamics (CFD). The numerical methodology was validated against experimental data, and the Realizable k-ε turbulence model was selected because it showed better agreement. The numerical results were evaluated in terms of the flow lines around the rudders, pressure coefficient distributions, and lift and drag coefficients. The results indicate that the anode shape has a noticeable influence on the flow characteristics around the rudder. The rectangular anode generated larger reverse flow regions and stronger flow disturbances than the semi-elliptical anode, resulting in higher drag coefficients. In contrast, the semi-elliptical anode produced smoother pressure coefficient distributions and smaller reverse flow regions. Moreover, oscillations in both lift and drag forces became more significant at higher angles of attack, particularly at 20° and 30°, which may increase the possibility of vibration. Overall, the results suggest that semi-elliptical anodes provide more favorable hydrodynamic performance than rectangular anodes while maintaining the cathodic protection function.