Laminar drag reduction in closed channel using bioinspired textured surfaces

Low flow drag is of great importance to a variety of engineering applications, and an effective way to achieve low drag is to use bioinspired micro-structured surfaces. This work aims to reduce the skin-friction drag in closed channel flow using textured surfaces inspired by leaves of indocalamus and rice. The channel formed by a polydimethylsiloxane chunk and a silicon wafer was fabricated to study drag reduction behavior for water or liquid paraffin oil in laminar flow. Bioinspired textures were processed on silicon wafer surface using deep silicon plasma etching method. We measured the pressure drop of water or paraffin oil passing through textured channels with different velocities. The maximum pressure drop reduction for the paraffin oil flow with low velocity (Re≈1) and for the water flow with high velocity (Re<1000) were about 5.1% and 27.3%, respectively. We also presented the contact angles of bioinspired textured surface, and then proposed mechanisms to explain the drag reduction. The hydrophobicity leading to the changing from the liquid-solid interface to the liquid-air interface is believed to provides the drag reduction for water flow, while the thin oil film formed on the textured surface due to the oleophilicity helps to reduce the oil flow drag.