Vol 76 No 3 76302

Abstract

Over the past quarter-century, substantial research has been conducted on the potential of dimpled surfaces to passively reduce turbulent friction resistance. This potential is particularly intriguing in the context of external flows, particularly with applications in the transportation sector, such as maritime vessels, rail systems, and aerial vehicles. However, the literature presents conflicting findings and interpretations about the performance of the dimples and the underlying physical mechanisms of the flow. Furthermore, many of the studies do not address the requirements for assessing the efficiency regarding practical engineering, such as high Reynolds number flow and open boundary layer conditions. In this study, the effect of dimpled surfaces on resistance reduction was experimentally investigated. A specialized testing bed, capable of accommodating large test plates, was designed for use in a cavitation tunnel facility. This setup allowed for the achievement of a high Reynolds number range suitable for practical applications, while ensuring that external flow conditions were met. Critical parameters affecting resistance reduction performance such as coverage ratio and boundary layer thickness, were also examined. The resistance values obtained within a broad experimental matrix suggest that, under favourable conditions, dimpled surfaces can be highly effective in terms of energy efficiency. The insights and interpretations drawn from these findings are expected to provide valuable guidance for future research.