Spanwise Airfoil Transition for Improved Low-Reynolds-Number Aerodynamics of a Stationary Finite-Span Blade

Low-Reynolds-number flows are susceptible to premature boundary-layer separation and stall, which can substantially reduce the aerodynamic efficiency of small blades. In this study, a variable-section twisted blade, designated FX-01, is investigated using computational fluid dynamics with the correlation-based Transition SST model. The blade incorporates a smooth spanwise transition between two cambered airfoil sections, together with linearly varying chord and twist distributions. Its aerodynamic performance is compared with those of two full-span reference blades over a range of prescribed global blade angles and freestream velocities. The numerical method is assessed against published low-Reynolds-number experimental data for a finite-span NACA4412 model. At V = 8 m/s, FX-01 achieves a maximum lift-to-drag ratio of approximately 9.1 at a prescribed global blade angle of αg = 15°, compared with approximately 8.85 and 6.42 for the NACA4412 and NACA4418 reference blades, respectively. At αg = 15°, FX-01 reaches a maximum lift-to-drag ratio of approximately 13.06 at V = 28 m/s. This peak value is 5.0% and 25.1% higher than the respective maximum values of the NACA4412 and NACA4418 reference blades over the investigated velocity range. The flow-field visualizations indicate that FX-01 produces a smoother spanwise pressure distribution and a less concentrated low-speed region in the displayed wake under the investigated conditions. Within the limitations of the steady-RANS framework, the results indicate that the coordinated spanwise variation in airfoil section, chord, and twist is associated with favorable predicted aerodynamic efficiency for the stationary finite-span blade under the investigated low-Reynolds-number conditions.