Turbulent drag reduction by spanwise wall forcing. Part 1. Large-eddy simulations

Turbulent drag reduction (DR) through streamwise travelling waves of the spanwise wall oscillation is investigated over a wide range Reynolds numbers. Here, in Part 1, wall-resolved large-eddy simulations channel flow are conducted to examine how frequency and wavenumber wave influence DR at friction numbers $Re_\tau = 951$ $4000$ . The actuation parameter space restricted inner-scaled (ISA) pathway, where achieved direct attenuation near-wall scales. level turbulence attenuation, hence DR, found change with Stokes layer protrusion height $\ell _{0.01}$ A frequencies identified attenuates turbulence, lifting up cycle generation thickening viscous sublayer; this range, increases as $30$ units. Outside strong shear strain enhances leading drop increasing We further find that, within our number space, ISA pathway has power cost that always exceeds any savings. This motivates study outer-scaled 2, actuating motions.