Vortex shedding and aerodynamic performance of an airfoil with multi-scale trailing edge modifications

An experimental investigation was conducted into the aerodynamic performance and nature of the vortex shedding generated by truncated and non-flat serrated trailing edges of a NACA 0012 wing section. The truncated trailing edge generates a significant amount of vortex shedding, whilst increasing both the maximum lift and drag coefficients, resulting in an overall reduction in the maximum lift-to-drag ratio (L/D) compared to a plain NACA0012 wing section. By decreasing the chevron angle ($\phi$) of the non-flat trailing edge serrations (i.e. by making them sharper), the energy of the vortex shedding significantly decreases and L/D increase compared to a plain NACA0012 wing section. Fractal/multi-scale patterns were also investigated with a view to further improve performance. It was found that the energy of the vortex shedding increases with increasing fractal iteration if the chevron is broad ($\phi \approx 65^{\circ}$), but decreases for sharper chevrons ($\phi = 45^{\circ}$). It is believed that if $\phi$ is too big, the multi-scale trailing edges are too far away from each other to interact and break down the vortex shedding mechanism. Fractal/multi-scale trailing edges are also able to improve aerodynamic performance compared to the NACA 0012 wing section.