Enhancing gas film stability by alternating superhydrophobic and hydrophobic surfaces for stable drag reduction

Superhydrophobic surfaces can significantly reduce the resistance of underwater vehicles, but as the speed increases, the gas film is prone to be destroyed, leading to a decrease in the drag reduction effect or even an increase in the drag. Therefore, enhancing the stability of the gas film is crucial for maintaining the drag reduction effect. Inspired by the honeycomb array pit structures, the high adhesion hydrophobic properties of rose petals, and the wetting gradient surface of Namib desert beetles, an alternating superhydrophobic and hydrophobic surface (ASHHs) was constructed by femtosecond laser to enhance the stability of the gas film. The high adhesion hydrophobic surface (HAHs) provides greater adhesive force, allowing the gas film to firmly pin at the junction of a low-adhesion superhydrophobic surface (LASHs) and HAHs, thereby enhancing the stability of the gas film. The critical failure velocity of ASHHs can reach 2.3 m/s, which is significantly greater than that of low-adhesion superhydrophobic surface samples (LASH-S) (1.7 m/s). ASHHs maintains a stable drag reduction effect of 37% at a velocity of 2.3 m/s, while that of LASH-S is only 6%. It is envisioned that such superhydrophobic surfaces that enhance gas film stability should find widespread applications in minimizing resistance and reducing energy consumption in the marine engineering field.