Vacuum casting replication of micro-riblets on shark skin for drag-reducing applications

A vacuum casting method to replicate shark skin surface accurately in large area was investigated to overcome some difficulties in the replication process. The fresh shark skin was pretreated as a replication sample, and the replication mold of shark skin was manufactured by casting the unsaturated polyester resin under vacuum and laying the multilayer glass fibers. Under vacuum condition, silicone rubber was poured into the resin mold to obtain the replication film of the shark skin with micro-riblets. The contour of the micro-riblet was measured by a Talysurf CLI2000 machine to evaluate the replication accuracy. Based on the contacting angle measurement, the hydrophobic property of the micro-ribletʹs surface was investigated. It was found that the vacuum casting method was an effective replication technology which was suitable to form large-area and highly accurate micro-riblets on the surface of the shark skin. The experiment of drag reduction was conducted in a water tank. Based on the experimental results, the replicated film of shark skin played a significant role in reducing drag. The maximum and minimum of drag reduction rate were 18.6% and 9.7%, respectively.