Experimental investigation of the aerodynamic performance of a tubercle airfoil with amplitude modulation

The aim of this study is to investigate the effects of humpback whale fin geometry, which is modeled with a more realistic approach on the leading-edge of symmetrical airfoil models at low Reynolds numbers (Re), on airfoil aerodynamic characteristics. To understand the effect of this leading-edge tubercle, an experimental study was performed via pressure measurement, smoke wire, tuft and surface oil flow visualizations as well as detailed force measurement at a wind tunnel. Experiments were conducted in the range of 5×104 - 1.2×105 of Reynolds number by producing 30 for NACA 0015 and 5 for NACA 0020 different models with leading-edge tubercles. According to the flow visualization results, unique flow structures like counter-rotating vortex pairs, wavy trailing edge separation, periodic and aperiodic flow patterns were obtained by disrupting the laminar separation bubble formation in the straight airfoil with the help of the tubercle airfoil. Although the maximum CL of the wavy airfoil models decreased with increasing Re, the maximum CL of the wavy airfoil models were higher than the straight airfoil models at poststall regions. Among the NACA 0015 and 0020 with leading-edge tubercle airfoil models, W15 model, having the parameters a1=0.025c, a2=0.0125c, 1=0.5c and 2=0.125c, was determined as the highest aerodynamic performance model especially after stall angles.