INVESTIGATION OF FLOW OVER NACA0021 AIRFOIL WITH LEADING-EDGE TUBERCLES USING TRANSITION-BASED HYBRID RANS/LES MODEL

The present paper numerically investigates flow control over NACA0021 airfoils by applying a lead-ing-edge tubercle to improve wind turbine performance at a transitional Reynolds number (Re) re-gime. The study includes simulations over the unmodified airfoil and modified airfoil operating at Re = 120,000 using a kT-kL-omega based delayed detached eddy simulation model. The calculations include both the prestall and poststall regions, while the performance of the mean flow aerodynamic proper-ties, such as pressure, lift, skin-friction, and drag coefficients, is also investigated in the presence of tubercles. The spanwise flow over the modified airfoil interacts with the primary flow. The turbulent separation is delayed compared to the unmodified airfoil, thereby significantly improving the stall be-havior and flow behavior in the poststall region. The modified airfoil provides the gradual stall behavior against the steep stall behavior for the unmodified airfoil. To optimize the tubercle configuration, the study considers two modified airfoils with different combinations of amplitude and wavelength. The unsteady analysis, including the reduced-order modeling, i.e., 3D proper orthogonal decomposition (POD), characterizes the dominant vortical structure of the flow to evaluate the improvement in the aerodynamic performance of the modified airfoil. The model decomposition for flow over the airfoil helps to provide a deeper understanding of the flow control phenomenon.