Hydrodynamic modeling and experimental validation of a cycloidal propeller

In this paper, a lower-order unsteady hydrodynamic model of a cycloidal propeller along with in-house experiments to validate the model is presented. Towards this, the hydrodynamics of a cycloidal propeller is investigated thoroughly and various underlying physical phenomena such as dynamic virtual camber, effects of near and shed wake, leading-edge vortices are rigorously modeled. It is shown that the chord-wise variation of incidence velocity angle on cycloidal propeller blade is manifested as dynamic virtual camber, which depends on curvilinear flow geometry, pitch angle, pitch rate and inflow distribution. By including all these effects together, a generalized expression of additional lift due to virtual camber effect is developed. To capture the effects of near wake, a nonlinear lifting line model is incorporated. Rapid pitching of rotor blades produces unsteady phenomena such as strong leading-edge vortices and shed wakes. Polhamus leading-edge-suction analogy is applied to model leading edge vortex. To capture the effects of shed wake, a method based on Theodorsen's approach is developed. A modified Double Multiple Streamtube (D-MS) model is used for modeling the complex inflow characteristics of a cycloidal propeller. The present hydrodynamic model is validated with measured time-history of forces obtained from in-house experiments at low Reynolds numbers.