Manufacturing tolerance effects on ship rudder force/cavitation performance. Discussion

Rudder manufacturing tolerances can have an effect on rudder lift, drag, torque, cavitation, and surface erosion. An unstructured, incompressible Reynolds-averaged Navier-Stokes Computational Fluid Dynamics code, U 2 NCLE, is used in this study to evaluate the effects of manufacturing variations on rudder lift, drag, and torque, in the absence of cavitation. Additionally, a boundary element method code, PROPCA V, is used to analyze the effects of manufacturing tolerances on rudder cavitation inception speed. This study investigated: (1) leading edge droop, (2) trailing edge twist, (3) spanwise twist, (4) longitudinal misalignment, and (5) transverse misalignment, as well as certain combinations of these effects, on a typical navy type spade rudder. The resulting computations for the deformed rudders revealed that construction variations which result in trailing edge twist have a significant impact on the rudder's torque coefficients. The results also showed the effects were additive when multiple manufacturing deformations were applied on the same side of the rudder, but subtractive when applied on opposite sides. For the cavitation study, the resulting computations for the deformed rudders reveal that construction variations which result in leading edge droop have the greatest effect on rudder cavitation.