Manufacturing Tolerance Effects on Ship Rudder Force/Cavitation Performance

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, U2NCLE, 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, PROPCAV, 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.

Effect of Transverse Misalignment on Natural Convection From a Pair of Parallel, Vertically Stacked, Horizontal Cylinders

Experiments were carried out to determine the effects of transverse misalignment on the natural convection heat transfer characteristics of a pair of equitemperature, parallel horizontal cylinders situated one above the other. During the course of the experiments, which were performed in air, the transverse offset was varied systematically at several fixed vertical separation distances, while the Rayleigh number ranged from 2 × 104 to 2 × 105. At small vertical separations, transverse offsetting causes an increase in the upper-cylinder Nusselt number (up to 27 percent) compared with that for the perfectly aligned case (i.e., no offset) and, furthermore, the Nusselt number is responsive to small offsets. On the other hand, at larger vertical separations, the offset-affected upper-cylinder Nusselt number is lower (by up to 20 percent) than the no-offset value but is quite insensitive to small offsets. At large transverse offsets, the upper-cylinder Nusselt number slightly exceeds that for a single cylinder, with the increase being due to a horizontal airflow induced by the acceleration of the lower cylinder’s plume. For all of the cases investigated, the lower-cylinder Nusselt number was virtually identical to that for a single cylinder.