Flow Characteristics of Drag Reducing Solid Wall

Abstract

In order to clarify laminar drag reduction and the slip velocity on a hydrophobic surface, the pressure loss of a rectangular duct was measured applying the various kinds of the wall surface qualities to duct inner wall. Test wall surfaces were classified three types by the surface characteristics, which were hydrophobic coating surface, fine rectangular groove surface and fine rectangular groove with hydrophobic coating. Direction of the fine rectangular groove are parallel, vertical and random in the flow direction, and the widths are 5 and 10 mm. For fine rectangular groove with hydrophobic coating surface, it was clarified that the laminar drag reduction occurred in the Reynolds number range of 150<Re<770. The maximum drag reduction ratio is 12.6% at Re=649. The Reynolds number range in which the drag reduction occurred increased with decreasing the width of the groove, and the direction of the groove did not affect the drag reduction effect.