Aerodynamic characteristics of a symmetrical airfoil in the presence of segmentally distributed leading-edge tubercles

In recent decades, experimental and numerical studies have demonstrated that wings with leading-edge (LE) tubercles exhibit advantageous aerodynamic performance at high attack angles compared to their unmodified counterparts. A substantial portion of these studies employed a single sinusoidal function to design the tubercles applied along the entire span. In this study, two functions were utilized to design tubercles. This experimental study was conducted to evaluate the effects of segmentally distributed (i.e., equally spaced) LE tubercles on the aerodynamic characteristics (ACs) of the National Advisory Committee for Aeronautics (NACA) 0018 airfoils and to associate them with the flow patterns observed on the suction surface. To this end, five different airfoil models have been produced and tested. The models consist of one plain airfoil, one fully tubercled airfoil, and three segmentally tubercled airfoils. The test results were obtained at Reynolds numbers (Re) of 0.6×105 to 1.2×105. It has been determined that the distance between neighboring tubercled segments possesses a critical value with regard to performance enhancements in the post-stall regime. In the range below this critical distance, the tubercled segments lack the capacity to reattach the separated flow from the plain segments of the airfoil. Furthermore, the presence of a novel vortical structure (i.e., single rotating vortex cell, SRVC) under certain conditions was demonstrated qualitatively.