Reduction of turbulent skin-friction drag by passively rotating discs

A turbulent channel flow modified by the motion of discs that are free to rotate under action wall turbulence is studied numerically. The Navier-Stokes equations coupled nonlinearly with dynamical equation disc motion, which synthesizes fluid-flow boundary conditions and driven torque exerted wall-shear stress. We consider fully exposed fluid for only half surface interfaces fluid. thwarted in housing cavity ball bearing supports disc. For full discs, no drag reduction occurs because small angular velocities. most energetic response diameters comparable spanwise spacing low-speed streaks. perturbation analysis disc-tip velocities reveals two-way nonlinear coupling has an intense attenuating effect on response. reduced-order results show excellent agreement large diameters. a finite velocity, leading activity skin-friction over spinning portion while maximum entire walls 5.6%. dependence wall-slip velocity spatial distribution stress qualitatively match based available experimental data.