Propeller-Rudder Interaction Due to Loading and Thickness Effects

Abstract

The previous analysis of the propeller-rudder interaction problem by means of the lifting-surface theory has been modified to include the effects of thickness of both surfaces. The effect of propeller blade thickness and rudder thickness on the "flow displacement" in the field is taken into account by the "thin body" approach. The blade thickness effect on the loading of the propeller blade due to its nonplanar form, being small, is neglected. The resulting onset velocities on both lifting surfaces due to the thickness effects on the flow field are incorporated, together with the onset velocities due to hull wake and camber and incident angle of the surfaces, into the existing iterative procedure. The numerical procedure, which has been adapted to the CDC 6600 high speed digital computer, furnishes the steady and time-dependent pressure distributions on both lifting surfaces and the resulting hydrodynamic forces and moments. From the limited number of calculations, it is seen that the thickness effect does not change the general conclusions reached in the previous study of the interaction problem. The interaction apparently is governed principally by the loading effects. The mean and blade-frequency thrust and torque and the mean rudder force and moment are very little affected by the inclusion of thickness even at the smallest possible axial clearance between propeller and rudder. The influence of thickness is greater on the propeller bearing forces and bending moments, on the steady-state values more than on the unsteady, and decreases with increase in axial clearance. The thickness effect is most pronounced in the case of unsteady rudder forces and moments at certain axial clearances, varying cyclically with clearance.