Study of the effect of transverse and longitudinal surface patterns on drag-reduction in shear-thinning fluid

Abstract

To investigate the effect of surface pattern on drag reduction in non-Newtonian fluid, a pin-disc lubrication experiment is performed with a universal microtribotester system. In the experiment, polyoxyethylene water solution is used as the lubricant, and the longitudinal and transverse grooves are etched on the disc surface as different surface patterns. The experimental results show that the drag force on the pattern is not always higher than that on a smooth surface. The drag reduction effect caused by the surface pattern occurs in the Newtonian field of the fluid, not in the shear-thinning field, as shown by the numerical results based on the CFD method. The drag on side walls of the transverse and grooves longitudinal cannot totally compensate the loss of drag on the bottom walls of the grooves: then the drag reduction occurs on surface patterns. On the other hand, the drag reduction effect caused by the surface pattern is weakened by the shear-thinning viscosity of the fluid.