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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

DRAG REDUCTION IN TURBULENT CHANNEL FLOW WITH TWO-TIERED SUPERHYDROPHOBIC WALLS

Richard Perkins
Department of Mechanical Engineering, Brigham Young University, Provo, Utah, 84602

Julie Crockett
Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A.; Department of Mechanical Engineering, Brigham Young University, Provo, Utah, 84602

Daniel Maynes
Brigham Young University, 435 Crabtree Building, Provo, Utah 84602, United States

Abstract

Drag reduction measurements are made in a channel with micro-structured superhydrophobic walls in combination with larger scale turbulence reducing riblets. Pressure drop and PIV measurements across surfaces exhibiting superhydrophobicity, riblets, and hybrid surfaces with both drag reducing mechanisms are presented. Micro-ribs etched in silicon and coated with Teflon provide superhydrophobicity. Larger scale riblets are deposited every 200 microns and extend nearly 100 microns above the ribs effectively dampening spanwise turbulence. PIV measurements are used to explore velocity and shear stress profiles where one channel wall is composed of a structured test surface and the other is smooth. These profiles allow estimation of friction factors and overall drag reduction. Reynolds numbers ranging from 3.5 × 103 to 2.3 × 104 are explored. A modest drag reduction was observed for the riblet only surfaces but the hybrid surfaces composed of both micro-ribs and riblets show the greatest drag reduction.

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