Abstract
We experimentally studied the stability of the gas (or plastron) trapped on superhydrophobic surface (SHS) consisting of transverse grooves in turbulent flows. The experiments were conducted in a turbulent channel flow facility, where the channel height was 6.4 mm, the mean flow speed varied from 0.5 to 4.5 m/s, and the Reynolds number, based on mean flow speed and channel height, ranged from 3300 to 29 000. The 50 × 50 mm2 SHS was installed at the fully developed flow region. The status of the gas layer on the SHS was measured by reflected-light microscopy and bright-field microscopy. We found that as the Reynolds number increased, the SHS experienced a sudden wetting transition from the Cassie–Baxter state to the Wenzel state. A metastable state, where the liquid partially filled the grooves, was not observed, probably because the exposed surface textures acted as a rough wall and increased the near-wall turbulence. Furthermore, we found that the wetting transition occurred at a higher Reynolds number with decreasing texture gap, increasing texture height, and increasing texture width. For SHS with small texture heights, the experimentally measured critical Reynolds number for wetting transition agreed well with a theoretical model based on the balance between wall pressure fluctuations and surface tension at the gas–liquid interface. Our results enhance the fundamental understanding of SHS stability in turbulent flows and will guide the design of stable SHS for reducing turbulent drag.