Plastron stability of super-hydrophobic surface with transverse grooves in turbulent flows

We experimentally studied the stability of the gas (or plastron) trapped on super-hydrophobic surface (SHS) consisting of transverse grooves in turbulent flows. We systemically varied the groove width (g), texture height (h), and texture wavelength (λ) in the range of 200 to 800 µm. The experiments were performed in a turbulent channel flow facility, where the mean flow speed varied from 0.5 to 6 m/s and the Reynolds number based on mean flow speed and channel height Re_m varied from 2000 to 24000. The status of gas layer on SHS was imaged by a reflected-light microscopy. We found that as increasing Reynolds number, the SHS experienced a sudden wetting transition from Cassie-Baxter state to Wenzel state. A metastable state where the liquid partially filled the grooves was not observed. Moreover, we found that the wetting transition was delayed and occurred at a higher Reynolds number as increasing h, reducing g, and increasing λ. The critical Reynolds number Re_cr for wetting transition was captured by models based on the force-balance at the gas-liquid interface. Last, we showed that grooves with V-shape maintained a stable plastron in turbulent flows at a higher Reynolds number.