Study on surface fabrication and drag reduction performances of gradient hydrophobic aluminum alloy

An underwater superhydrophobic (SH) surface drag reduction is an effective drag reduction method. However, drag reduction failure is likely to occur on the SH surface at high water velocity. To solve this problem, we designed an SH and hydrophilic interphase (SH-H) and gradient SH-H (GSH-H) structure on the surface of aluminum alloy by laser etching and micro-electric discharge machining (EDM) methods. The laser scanning interval of the SH segment was 10 mu m while that of the hydrophobic segment was 250 mu m. The hydrophilic segment was cut by micro-EDM without laser processing. The SH and hydrophobic segments were treated with fluor silane to obtain surfaces with low surface energy. In this work, the flow field characteristics of the SH-H and GSH-H model with different Re were simulated by setting a sliding wall for numerical calculation. the drag reduction ability of samples for varying Reynold number (Re) were studied in pressure difference drag-reduction channel. The simulation results show that the SH-H structure can still seal a thin gas film at Re = 4000, and has a good drag reduction effect. The experiment results show that the drag reduction on the SH-H surface was up to about 45.45%. Moreover, when soaking in water for 30 min and Re = 3500, the sample surface still had the drag reduction effect, and the prepared SH surface had good mechanical stability. It is expected that this research can provide reference and ideas for solving the problem of gas film loss on the SH surface.