Drag reduction characterization of spray-on superhydrophobic surfaces in a turbulent channel flow

Previous studies have shown that randomized spray-on superhydrophobic surfaces (SHS) achieve drag reduction (DR) at high Reynolds numbers (Re). DR of SHS depends on the Re, with DR reducing with increased Re due to loss of gas pockets. Despite these studies, the role of the roughness profile of surfaces and the underlying chemical composition of the SHS under consideration on the observed DR performance is yet to be fully understood. In this study, drag produced by several SHS made with Fluorinated Silica NanoParticles (FSNP) and Fluorodecyl Polyhedral oligomeric SilSesquioxane (FPOSS) are tested in a turbulent channel flow. These materials are sprayed at various pressures onto a stainless-steel substrate to achieve different roughness profiles. Drag produced by the surfaces is estimated based on pressure drop measurements in a turbulent channel flow for ReH ranging from 10000 to 40000. Measured drag is compared with a hydrodynamically smooth surface to quantify DR.