Numerical Investigation of Spin Ratio Optimization for a Single-Rotor Sail and Aerodynamic Performance Evaluation of Multi-Rotor Sail Systems Based on Wake Interaction Characteristics

In this study, the aerodynamic performance of single- and multi-rotor sail systems was numerically investigated under various inflow directions and array configurations using Computational Fluid Dynamics (CFD) simulations. For a single-rotor sail, the optimal spin ratio (SR) for each wind direction was derived from the energy efficiency index, and an appropriate spacing distance of 9D was identified, within the present steady-RANS framework, as a preliminary guideline based on wake-recovery characteristics. Using these findings, four array configurations were established to reflect the practical installation conditions of a medium-range (MR) tanker. The wake interference and aerodynamic performance variations in each configuration were quantitatively compared and analyzed. The results showed that the average lift in all arrays remained within ±1% of that of a single-rotor, and the 1 × 1 × 1 array exhibited the most stable performance. These findings confirm that the wake-based spacing design and wind direction-dependent SR optimization proposed in this study are crucial for maintaining aerodynamic stability and improving efficiency in multi-rotor sail systems. It is expected that the results of this study will contribute to establishing design guidelines and operational strategies for the practical applications of rotor sails on ships.