Drag Reduction on Micro-Structured Super-hydrophobic Surface

Abstract

This paper presents numerical and experimental investigation of drag reduction on the micro-engineered surface, which is inspired by nature. Computational simulation has been performed to examine the flow characteristics on both smooth and rough surfaces, and an experimental investigation is conducted by using artificial super-hydrophobic surface fabricated by MEMS fabrication technique. The artificial surface is made of silicon wafer, where micro-structured with hydrophobic properties has been successfully mimicked. Effect of rough surface has been numerically examined by measuring the velocity profile and skin friction coefficient (c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ) at grooves wall, which are compared with those of smooth surface. Unlike smooth surface, it is verified that the vortices flow are generated inside the valley of groove and affected the skin friction coefficient along the grooves wall to be small inside grooves valley region. Because of this small skin friction, the total drag may be reduced by the rough surface. The effect of grooves structure is also demonstrated by varying the shape and aspect ratio of grooves. This effect shows that high aspect ratio of groove generates different vortex shape inside the grooves valley and sudden increment of velocity profile near the wall was existed. The local skin friction value of grooves with aspect ratio 1 and 2 shows almost the same level, meanwhile the grooves with aspect ratio 8 gives lower skin friction value.