On the aerodynamic performance of the leading-edge tubercle elliptic flapping airfoil in forward flight condition*

In this study, the aerodynamic performance of the flapping elliptic airfoil with and without the leading-edge sinusoidal tubercles was investigated using experiments and numerical simulations in the presence of an incoming flow having a Reynolds number of 5000. Here, the amplitude and wavelength of the tubercles were fixed at 0.125 and 0.5 times the airfoil chord, respectively. The effect of the flapping frequency on the airfoil aerodynamic performance was also accessed by varying the Strouhal number (St) between 0.2 to 0.6 while keeping the maximum effective angle of attack as 15^o. It is noticed that the time-averaged thrust coefficient (C_t) over a flapping cycle increases with St for both types of airfoils up to a critical St (=0.5) and degrades after that. In addition, the C_t values of tubercle airfoil are seen to be inferior compared to the smooth-edge airfoil at considered St. On the other hand, the tubercle airfoil's aerodynamic power requirement is less than smooth-edged airfoil, yielding a better aerodynamic efficiency at higher St. Moreover, the near wake structures of the tubercle airfoil with the counter-rotating vortex pairs between the crest and trough region are distinctive from that of the smooth-edged airfoil. Those details will be discussed in the presentation.