Fabrication of a micro-riblet film and drag reduction effects on curved objects

This paper presents the fabrication of a micro-riblet film (MRF) and the experimental results of the drag reduction effects of the MRF on curved objects. Riblets, grooves on the surface in stream-wise direction, are proven as an effective passive tool of the drag reduction. A MRF is fabricated with a polydimethylsiloxane (PDMS) micro-molding technique of which mold is fabricated with bulk micromachining. The MRF has two hundred ribs, on the 6 cm/spl times/6 cm area, of which height, spacing and length are 180 /spl mu/m, 300 /spl mu/m, and 6 cm, respectively. The drag reduction effects of the MRF on an NACA 0012 airfoil and a circular cylinder are examined with a particle image velocimetry (PIV) system and a 3-component load cell module, respectively, in a closed-type subsonic wind tunnel. The MRF provides about 4.3% drag reduction on the airfoil and 7.6% drag reduction on the cylinder when the freestream velocities of the wind tunnel are 3.3 and 3 m/s, respectively.