Drag reduction characteristics of the placoid scale array skin sup-ported by micro Stewart mechanism based on penalty immersed boundary method

Abstract

Sharkskin performs an excellent flow drag reduction property, leading to numerous biomimetic research to obtain artificial drag reduction structures for underwater vehicles. The existing work mainly focused on replicating or simplifying the morphology of the placoid scale, however, such bionic structures cannot fully reproduce the drag reduction effects of sharks swimming in natural environments. This is because the existing research has not considered the influence of the multi-degree freedom motion characteristics of the placoid scale. Therefore, a new bionic drag reduction skin is proposed by combining micro Stewart mechanisms and placoid scales, where the micro Stewart mechanism is able to achieve the multi-degree freedom motion characteristics. The numerical results indicate that micro Stewart mechanisms inhibit the generation and development of the streamwise and spanwise vortex structures in the bionic placoid scale array, which can delay flow separation and improve the drag reduction effect of the placoid scale array. Compared with the bionic placoid scale skin and the blade groove skin without multi-degree freedom motion foundation, the new bionic skin achieves relative drag reduction efficiency of 15.78 % and 14.18 % at maximum, respectively, by reasonably adjusting the bionic skin parameters including the leg stiffness, leg damping, upper platform mass, upper platform center of mass height of the micro Stewart mechanism and the skin element distribution spacing. The research presents a novel sharkskin bionics design and reveals the mechanism of skin drag reduction to some extent.