Passive Flow Control of a NACA 0015 Wells Turbine Airfoil Using a Single Inclined Suction Slot

This paper investigates the aerodynamic performance of a NACA 0015 Wells turbine airfoil equipped with a single inclined suction slot as a passive flow control technique. Steady Reynolds-Averaged Navier–Stokes simulations with the k-ω SST model were performed in ANSYS Fluent V.2021 for a two-dimensional airfoil with six slot inclination angles (15° to 90°) at five angles of attack near stall. The steady model overpredicts the measured torque coefficient but reproduces its variation through stall, and a transient simulation at the stall angle changes it by less than 1%, so the steady model is used to compare configurations. All slots improve the torque coefficient compared with the baseline airfoil. Based on the discrete relative L2 improvement, the 30° slot gives the highest gain (28.64%) and the 90° slot the smallest (21.33%), while the 15°, 45°, and 60° slots remain within 1.2 percentage points of the 30° slot. Surface pressure and skin-friction distributions show that the slots raise the suction peak and move the separation point downstream, the 30° slot more than the 90° slot. Within the limits of a steady two-dimensional model, a single inclined suction slot is thus a promising passive flow control technique for Wells turbine blades near stall.