Impact of groove filling due to particle accumulation on the drag reduction performance of riblets in turbulent channel flow

This study aims to clarify particle adhesion characteristics on riblet surface using direct numerical simulations and experiments. Numerical simulations of particle-laden, fully developed turbulent channel flow with rectangular riblets were performed to investigate the influence of particle adhesion on drag reduction. A one-way coupling method was employed, in which the flow affects the particles but the particles do not affect the flow. The spatial distribution of particle adhesion on the riblet surfaces was evaluated. Most particles adhered to riblet crests and the upper half of the sidewalls owing to tumbling motion within the grooves. Outdoor and laboratory experiments also revealed nonuniform particle accumulation on the riblet groove floor. The riblet shape was then modified based on the particle adhesion distribution, and a series of numerical simulations with different shapes was performed. The results reveal a decrease in the skin-friction drag reduction effect compared with the initial riblet configuration.