Prediction of Steady and Unsteady Loads and Hydrodynamic Forces on Counterrotating Propellers

Abstract

Linearized unsteady-lifting-surface theory has been applied in the study of counterrotating propeller systems with equal or unequal number of blades operating in uniform or nonuniform inflow fields when both units are rotating with the same rpm. The mathematical model takes into account as realistically as possible the geometry of the propulsive device, the mutual interaction of both units and the three-dimensional spatially varying inflow field. The propeller blades lie on a helicoidal surface of varying pitch, have finite thickness and arbitrary planform, camber and sweep angle. The inflow field of the after propeller is modified by taking into account the effect of the race of the forward propeller, so that potential and viscous effects of the forward propeller are incorporated. These additional effects play an important role in determining the unsteady loading of the after propeller. This, together with some refinements introduced in the numerical procedure, has brought the theoretical results into better agreement with experiments. A computer program has been developed adaptable to a high-speed digital computer (CDC 6600-7600, Cyber 176) for counterrotating systems of equal and unequal number of blades, in uniform flow, for comparison with existing experiments.