Investigation on the Effect of Transverse Grooves on Friction Force

Abstract

The effect of transverse grooves on friction force was considered, differing from the longitude riblets. A discontinuous traveling wave distribution was developed based on the traditional continuous one. The friction force was measured directly in a high-speed water tunnel with flow velocity varying from 17 to 22m/s. The force increased quadratic with the increasing of velocity. Compared with smooth surface, the friction drag reduction was about 12.5%. The computational fluid dynamics simulations, using RNG k-e turbulent model, showed that the vortex was formed in the groove. On the upside of the vortex, the revolving direction of the fluid was in consistent with the main flow, which decreases the flow shear stress rate. The vortex increases the height of the turbulent boundary layer, and decreases the turbulent intensity of main fluid field, thus decreases the slope of velocity and the friction force. Correspondingly, the transverse grooves induce pressure drag. When the increase of pressure drag is less than the decrease of the friction force, the total drag is decreased. The function of the vortex in the groove was like a rolling bearing. In this wok, the computational simulation explained the experimental results well.