CFD-based investigation of air temperature effects on Savonius rotor performance under dynamically similar conditions

This study investigates how air temperature affects the aerodynamic performance of a Savonius rotor under dynamically similar conditions at a fixed Reynolds number Re. Two-dimensional unsteady Reynolds-averaged Navier–Stokes simulations, in both compressible and incompressible formulations, are conducted for five air temperatures T₀ between 278 and 323 K. For each case, thermophysical properties and wind speed co-vary with T₀ to keep Re constant. The compressible and incompressible solutions differ by less than 1% in the power coefficient C_p over all conditions, confirming that compressibility effects are negligible. Although temperature acts as a passive scalar, influencing turbine aerodynamics indirectly through property scaling rather than as an active thermodynamic variable, temperature-dependent properties strongly modify both dimensional and nondimensional outputs: the peak power at a tip-speed ratio of 1.0 increases by up to 90% as temperature rises to 323 K, while the highest C_p occurs at around 303 K, approximately 2.1% higher than at 323 K. This trend is opposite to that reported in previous constant-velocity studies, where Re effects dominated the observed performance changes. The findings demonstrate that temperature-dependent property scaling alters both rotor efficiency and wake behavior and should therefore be considered in performance assessment and wind-energy resource planning.