Independent Effects of Blade Number and Solidity on Cyclorotor Hover Performance: A Parametric CFD Study for Design Optimization

Abstract

The influence of blade number and rotor solidity on cyclorotor hover performance remains insufficiently understood because previous studies have generally varied these parameters simultaneously or investigated them through separate one-factor analyses. This work examines their independent effects using a two-dimensional unsteady Reynolds–Averaged Navier–Stokes model in which blade number (2–8) and rotor solidity (0.24–0.60) are varied independently across 26 geometrically feasible design points, at constant rotor radius and rotational speed. The model is validated against published experimental data for the same rotor before the parametric analysis is performed. At fixed rotational speed, increasing solidity raises both the thrust and power coefficients and lowers power loading. Because power loading is disk-loading-dependent even for an ideal rotor, however, this apparent penalty largely reflects a change in operating point rather than a loss of aerodynamic efficiency: compared at matched disk loading, efficiency varies only weakly with solidity except in the corner of the design space that combines high solidity with a long blade chord, and an interior efficiency optimum emerges near σ≈0.36 for blade counts N=4–8, reconciling the present results with the chord-to-radius optimum reported in the literature. Blade number has only a secondary influence on mean performance at constant solidity, consistent with classical rotor theory; azimuthally resolved loads, however, show peak-to-mean thrust ratios of 3–4 for two- and three-bladed rotors, a design constraint invisible in cycle-averaged metrics.