Drag Reduction in Flow through Square and Rectangular Ducts with Highly Water-Repellent Walls.

Abstract

Laminar drag reduction for Newtonian fluids in highly water-repellent ducts has been reported. Measurements were carried out to investigate pressure losses in square and rectangular horizontal ducts with highly water-repellent walls and with wetted walls, with aspect ratios of 1.0 and 0.5, respectively. Tested fluids were tap water and aqueous solutions of glycerin at concentrations of 10 and 20 wt%. The maximum drag reduction ratio of tap water was about 22% for ε=1.0. The friction factors in highly water-repellent wal ducts in laminar flow region sifts parallel to the exact solution curve, which was obtained by assuming no slip conditions. These results suggest that the principal cause of drag reduction is fluid slip on the wall.