Viscous Drag Reduction with Surface-Embedded Grooves

Turbulent drag reduction in wall-bounded flows is investigated experimentally by considering the dynamic effects provoked by large variation of anisotropy in the velocity fluctuations. It is shown that high drag reduction is obtained when the velocity fluctuations near the wall reach the statistically axisymmetric state with invariance under rotation about the axis aligned with the mean flow. Deductions based on the analysis of near-wall turbulence leads to the design of the grooved surface topology, for which it is demonstrated experimentally that can produce a maximum drag reduction of DR ≃ 25%. The drag reduction effect persisted in a narrow range of flow velocities and for the reported experimental conditions correspond to groove dimensions of about 0.8 viscous length-scale.