Hydrodynamic modeling and experimental validation of cycloidal propeller in translational motion

In this paper, detailed development of an unsteady hydrodynamic model of a cycloidal propeller in translational motion (i.e. surging, heaving or combination of both) is presented. Towards this, effect of translational velocity on several hydrodynamic phenomena such as virtual camber, inflow characteristics are rigorously modeled. It is shown that the freestream velocity due to translational motion changes curvilinear geometry of the flow associated with cycloidal propeller, which changes chord-wise variation of incident flow velocity angle on the blade and hence the dynamic virtual camber and incidence. The model predictions are compared with test data from a novel experimental set-up in a water tunnel that measures instantaneous forces on a cycloidal propeller blade in translational motion. Analysis using the developed model demonstrates that the dynamic nature of virtual camber and incidence plays an important role in the force production of cycloidal propeller. Due to the complex interplay of virtual camber and blade kinematics, net side-ward force (or lift) of the cycloidal propeller increases while net propulsive force decreases as the advance ratio of cycloidal propeller is increased. At higher advance ratios, the cycloidal propeller blade experiences negative tangential force and extracts power from the flow near 180° azimuth.