Drag reduction characterization of spray-coated 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). However, the role of the roughness profile of surfaces and the underlying chemical composition of the SHS on DR is yet to be fully understood. In this study, drag produced by several SHS made with Fluorinated Silica NanoParticles (FSNP) and Fluoroalkyl Polyhedral Oligomeric SilSesquioxane (FPOSS) are tested in a turbulent channel flow. Drag produced by the surfaces is estimated based on pressure drop measurements in a turbulent channel flow for ReH ranging from 10000 to 40000 and compared with a hydrodynamically smooth surface. To understand the effect of external conditions on SHS performance, hydrodynamic pressure, and dissolved oxygen (DO) level in the flow are systematically varied. Results show a notable sensitivity of drag performance to these parameters. Preliminary Particle Image Velocity (PIV) measurements are discussed to elucidate the flow mechanisms underlying the observed trends.