Laser Preparation and Underwater Drag-Reduction Performance of Secondary Fractal–V Groove Composite Structures on the Surface of Equal-Diameter Revolution Bodies

The reduction of drag for both aircraft and underwater equipment has the potential to reduce their overall energy consumption. Consequently, research into the drag-reducing performance of metal surfaces has significant practical applications. However, there has been more research on the machining of grooves on flat surfaces and inside tubes and less research on the structure of drag-reducing grooves on the outside of circular rods. This paper presents a study in which laser etching technology is employed to machine a range of secondary fractal topologies and V-groove composite structures on the surface of equal-diameter stainless-steel bodies of revolution. The influence of different parameters on the surface properties of stainless-steel materials is analysed through the use of auxiliary positioning tools, adjustments to laser processing parameters and scanning path schemes, as well as the characterisation of the surface morphology of the processed stainless steel using super-depth microscopy, scanning electron microscopy, and other techniques. Subsequently, an underwater drag-reduction tester is employed to assess the drag-reduction efficacy of the optimised secondary fractal composite structure on the surface of the stainless-steel equal-diameter body of revolution. Subsequently, particle image velocity (PIV) tracking technology is employed to assess the surface flow field velocity and overall velocity average of the secondary fractal composite structure. The findings indicate that the secondary fractal composite structure exhibited a drag-reduction effect on the surface of the stainless-steel body of revolution only when the primary main groove had a width of 0.1 mm. Furthermore, an increase in the Reynolds number Re within the range of 4000 to 7000 resulted in a notable enhancement in the drag-reduction efficacy of the secondary fractal composite structure on the surface of the stainless-steel body of revolution. At Re values of 5000, 6000, and 7000, the corresponding drag-reduction rates were observed to be 5.15%, 5.28%, and 5.40%, respectively.