Experimental validation of a cycloidal rotor URANS CFD model and geometric parameter optimization

Abstract

Cycloidal rotors offer many properties that are beneficial to VTOL rotor concepts. Two examples are high manoeuvrability and low aerodynamic noise emission. These rotors use cyclically pitched axial blades to generate thrust and operate in highly unsteady flow regimes, including curvilinear flow and dynamic stall phenomena. The current work develops an unsteady, incompressible 3D URANS CFD simulation setup that models a given small-scale experimental rotor. Measurements and simulation are conducted at a relatively low and slim Reynolds number range of 12x10^3 ≤ Re ≤ 76x10^3. By comparison of simulation results and experimental data, the CFD setup is validated. The validated setup is used to investigate flow phenomena on the initial rotor configuration and further conduct multiple separate parametric studies to optimise the rotor's energy efficiency. The investigated parameters are the blades' pitch profile, the number of blades, blade span and the addition of endplates at the blade tips. The highest efficiency increase of 14% compared to the experimental rotor is hereby found when adding endplates. The most efficient pitch profile results with a pitch rod length of l_opt=87 mm. The optimal blade span aspect ratio is 6 and a four-blade rotor is most efficient. Further research may aim at conducting this optimisation in a wider Reynolds number range or finding an optimum of multiple variable parameters combined.