Numerical simulation on drag reduction in a pipe flow with a patterned riblet surface

The current study investigates the validation of slip boundary conditions in an internal piping flow comparing no-slip boundary conditions from the classical fluid mechanics with respect to viscous frictional losses occurring at a piping wall. Modifying the surface conditions result in slip boundary conditions that reduce the wall shear stress by the fluid viscosity. Such surface conditions were inspired by the surfaces of fast swimming shark skins, gecko, lotus leaves, etc., and engineers and scientists reported an average of 20% drag reduction obtained for internal flows with trying to mimic the bio-inspired surfaces such as riblets, wall oscillating surfaces, polymer additives, compliant coating, hydrophobic, and superhydrophobic surfaces. As the extensions of these efforts, this study conducted numerical simulation on riblet patterned wall surface to produce slip boundary conditions of an internal piping flow. A numerical approach is performed using commercial software to find slip effects of riblet patterned surfaces on internal pipe walls. Initially, the results from published references were validated by comparisons for no-slip, 95%, 90%, 80% and 50% slip boundary conditions. Then, whole patterned and half-patterned riblet surfaces were designed on the internal wall surfaces of 120 mm and 240 mm long rectangular ducts for the effect of the surfaces on the pressure drops and drag reductions on the surfaces. It was discovered that riblet patterned wall surfaces can reduce the pressure drops in a piping flow by the shear stress reduction at the surfaces, however theses surfaces should be applied after an entrance effect region where the surface shear stress can be increased by the riblet patterned surfaces