Near-hydrophobic-surface flow measurement by micro-3D PTV for evaluation of drag reduction

Abstract

This study reports the estimation of drag reduction effect, which is obtained from slip flow measurement in hydrophobic microchannels by direct measurement of near-wall velocity distribution. To reveal laminar drag reduction effect of hydrophobic surfaces, it is necessary to investigate near-microstructured-surface flow. In this study, we employed a hydrophobic surface, which has longitudinal microribs and microgrooves oriented parallel to the water flow direction in a microchannel, and measured a near-microstructured-surface flow by astigmatism particle tracking velocimetry (APTV) that enables to obtain the three-dimensional and three-component velocity profile. From the flow measurement results, the curvature and profile of liquid–gas interfaces formed at the microgrooves were obtained. Additionally, since the APTV has the ability to measure the three-dimensional velocity distribution near interfaces, it is possible to determine the shear stress on the interfaces if the interface position is known. Moreover, the procedure about a numerical simulation, which used the experimental results as a boundary condition was examined, and its verification in terms of the drag reduction effect estimation was conducted by comparing with experimental results.