The biomimetic propulsion of two tandem foils with different sizes

With numerical studies of two tandem foils, the effect of size gaps and distance between two tandem foils on reducing drag is presented. A symmetric 4-digit NACA0012 foil has been used as the outline of leading foil, while the trailing foil has been redesigned as multiple of scale down of leading one, by which the size gaps between two tandem foil can be non-dimensionalized as a parameter S_g. Moreover, the ratios of the spatial gaps between two tandem foils to the length of leading foil have been used as another non-dimensionalized parameter D_g to describe the effect of distance gaps on drag reduce. As a result, it is found that the leading foil would enjoy the biggest drag reduction at S_g = 1 and D_g = 0.3, as 24%. It is also revealed that the trailing foils would also enjoy an drag reduction or thrust increase, and the biggest drag reduction of trailing foils has been observed as 67%, moreover, the trailing foil would increase thrust when S_g = 2, as the biggest value is 37%.