Experimental Investigation of the Drag Reducing Effects of Riblets in Pipes.

摘要

The purpose of this investigation is to determine the drag reducing effects (as compared to a smooth surface) or riblets in both laminar and turbulent, fully developed pipe flow. A specially constructed split pipe provided convenient internal access for application of symmetric v-groove shaped riblets (3M's 0.003 and 0.006 inch riblet films). Riblet results, both with and without polymer, are in agreement with comparable studies in external boundary layer flows. Between 6% and 8% maximum drag reduction is achieved with riblets alone when h+(=s+) is between 11 and 15, and in dilute polymer solutions no significant difference in drag reduction is observed with the addition of riblets. Drag reduction was observed at values of h+ as low as 3, well within the viscous sublayer. At lower values of h+, within the laminar flow regime, neither a drag increasing nor decreasing effect was found despite more than doubling the surface area with the application of riblets. Polymers, Pipes, Riblets, Boundary layers, Reprints. (JES)