MEASUREMENT OF FRICTIONAL DRAG ON ALLIGATOR-SKIN-LIKE FEMTOSECOND SURFACE TREATMENTS

Abstract

This research sought to determine whether femtosecond laser surface processing (FLSP) is a viable alternative to anti-corrosive, hydrodynamic coatings. FLSP was applied to stainless steel plates to see its effect on frictional drag. The effect on drag was analyzed by comparing different FLSP application orientations, plate edge shapes, and plate geometries.

Drag testing was conducted in a custom water channel. Due to sensitive instrumentation (measuring in millivolts), the effect of plate variability was significant. Results confirmed that above surface growth (ASG) outperformed below surface growth (BSG), superhydrophobic plates outperformed superhydrophilic ones, and the 45° fabrication laser orientation outperformed the 90° one, all in reducing frictional drag. Thus, the combined characteristics of ASG, superhydrophobic plates, and 45° orientation, dubbed "alligator-like," were most effective at reducing frictional drag (46.6% reduction from control).

The effect of pressure on different FLSP-treated plates was studied, specifically the surface color change. No color change was evident, and it appeared the plastron could withstand 15 kPa. More sophisticated testing is required for greater pressures. While frictional drag reduction was seen, a comparison studying the same plate before and after FLSP treatment would increase the reliability of results, as uncertainty was a major concern.