Performance Optimization of Shrouded Rotors: Fixed vs. Variable Pitch in Hover and Forward Flight

This paper presents a comprehensive study on the aerodynamic design, analytical modeling, and computational validation of shrouded rotor systems, encompassing both fixed-pitch and variable-pitch configurations in hover and forward flight. An analytical framework based on Blade Element Momentum Theory is developed and validated against Computational Fluid Dynamics simulations employing the Multiple Reference Frame method in ANSYS Fluent. A 16-inch shroud is designed through a four-step procedure considering tip clearance, the diffuser expansion ratio, and the inlet lip radius, and multiple rotor configurations are optimized using genetic algorithms. The results show strong agreement between analytical predictions and Computational Fluid Dynamics, with thrust predictions across operating conditions. In hover, variable-pitch rotors achieve comparable thrust–power performance to fixed-pitch rotors, despite requiring only a single optimized geometry; performance variations are achieved through pitch adjustment. In forward flight, variable-pitch rotors maintain high efficiency over a broader range of advance ratios, whereas fixed-pitch rotors exhibit peak efficiency only at a specific design point. These findings highlight the superior adaptability of variable-pitch rotors for missions requiring efficient operation across both hover and forward flight and demonstrate the reliability of the proposed analytical model as a rapid design tool.