Accepted for publication in J. Fluid Mech. 1 Turbulent drag reduction through

This article has been accepted for publication in Journal of Fluid Mechan-ics, published by Cambridge University Press. The changes of a turbulent channel flow subjected to sinusoidal oscillations of wall flush-mounted rigid discs are studied by means of direct numerical simulations. The Reynolds number is Rτ=180, based on the friction velocity of the stationary-wall case and the half channel height. The primary effect of the wall forcing is the sustained reduction of wall-shear stress, which reaches a maximum of 20%. A parametric study on the disc diameter, maximum tip velocity, and oscillation period is presented, with the aim to identify the optimal parameters which guarantee maximum drag reduction and maximum net energy saving, the latter com-puted by taking into account the power spent to actuate the discs. This may be positive and reaches 6%. The Rosenblat viscous pump flow, namely the laminar flow induced by sinusoidal in-plane oscillations of an infinite disc beneath a quiescent fluid, is used to predict accurately the power spent for disc motion in the fully-developed turbulent channel flow case and to estimate localized and transient regions over the disc surface subjected to the turbulen