Drag reduction on micro-structured hydrophobic surfaces due to surface tension effect

Abstract

This article studies drag reduction rule and gas restoration and retention of hydrophobic surfaces numerically when taking into consideration the surface tension effect, the microstructure here is chessboard-like and the Reynolds number varies from 3,000 to 30,000. Results show that gas restoration and retention keep well, and a maximum drag reduction rate of approximately 30% has been gained at small Reynolds number(Re<15000). When Re is too large, water will swarm into microstructures, and keeping a good gas-liquid interface becomes difficult. Meanwhile, drag reduction rate remains variable and hydrophobic surfaces do not reduce drag. Through mechanical analysis we find that the influence of shear stress is weakened due to surface tension effect, thus the gas in microstructures can be effectively stored at low flow speed and drag is reduced.