Effects of micro-grooves and fluid viscoelasticity on friction drag reduction in a turbulent boundary layer

To meet the underwater drag reduction needs in engineering applications, one can draw on the drag reduction strategies of marine animals such as sharks, utilizing their surface groove structures and the secretion of viscoelastic drag-reducing mucus to achieve drag reduction effects. However, in the field of engineering research, efficient and accurate simulation methods for viscoelastic fluid flow are relatively scarce. There is an urgent need to develop efficient numerical simulation methods for viscoelastic fluids, and to analyse the drag reduction characteristics of the coupling between surface grooves and drag-reducing agents. Through large eddy simulation and re-development of the ANSYS Fluent platform, efficient and accurate simulation of viscoelastic fluid flow as well as wall infiltration method has been successfully realized. Quantitative analysis of drag reduction characteristics of surface structures and viscoelastic fluid additives within the Reynolds number range of 4×104 to 4×105 has been conducted. Moreover, the synergistic effect of micro-grooves and drag reducer infiltration on drag reduction has been deeply explored. It is found that the maximum drag reduction by the groove surface solely is below 20%, whilst the maximum drag reduction by viscoelastic drag-reducing agent infiltration on the smooth flat plate is up to 28.9%. Notably, when combining the groove structure with drag-reducing agent infiltration, the maximum drag reduction reaches up to approximately 70%. The mechanism for the drag reducing effect is analysed from the aspects of vortex structure evolution on the wall, velocity profile and drag-reducing agent diffusion. This establishes an efficient and accurate simulation method for viscoelastic fluid flow suitable for engineering research, providing an important reference and foundation for underwater drag reduction studies.