Bionic micro-cavitators for underwater vehicles: Cavitation performance and drag reduction

Natural cavitation has attracted considerable attention as a passive drag reduction technique because it requires neither external gas injection nor additional energy input. To enhance cavitation performance, cavitators are commonly employed; however, the additional drag they introduce may offset the resulting drag reduction benefit. Accordingly, this study proposes bionic micro-cavitators to promote cavity development while limiting the drag penalty relative to traditional designs. Three annular micro-cavitators with circular, triangular, and square meridional profiles were first screened based on drag coefficients and minimum static pressure. Subsequently, inspired by the smooth convex morphology of the dolphin's melon, bionic circular and triangular micro-cavitators were developed. Numerical simulations showed that the bionic circular micro-cavitator provided better cavitation and drag reduction performance than the traditional disk cavitator. At U∞ = 55 m/s, the bionic circular micro-cavitator achieved a maximum drag-reduction rate of approximately 38%, compared with approximately 27% for the traditional disk cavitator. In addition, although it incurred substantially higher pressure drag, the bionic triangular micro-cavitator exhibited the best cavitation performance, achieving full supercavitation at σ = 0.079, higher than σ = 0.055 for the other two cavitators. Experimental observations of cavitation and measurements of drag for the bionic circular micro-cavitator showed qualitative agreement with the numerical predictions. The present work may therefore provide a feasible new approach to cavitator design.