the fluid) can be obtained by carefully tuning the parameters of the oscillation. Another property of this flow that will be exploited in the following is that, once the flow field is averaged along the streamwise and spanwise homogeneous directions, the spanwise velocity profile agrees with the laminar solution of the so-called second Stokes problem [@quadrio-sibilla-2000; @choi-xu-sung-2002; @quadrio-ricco-2003], hence uncoupling from the complex dynamics of the all-encompassing turbulence. In the spirit of the wall-oscillation technique, research works have appeared on the drag reduction effects of forcing the turbulence by spanwise travelling waves [@du-karniadakis-2000; @du-symeonidis-karniadakis-2002; @karniadakis-choi-2003; @zhao-wu-luo-2004; @itoh-etal-2006; @yoon-etal-2006], by spanwise oscillating Lorentz forces [@berger-etal-2000; @pang-choi-2004; @breuer-park-henoch-2004; @lee-sung-2005], by spanwise oscillating suction and blowing [@segawa-etal-2005], and by steady streamwise oscillations of the spanwise wall velocity [@quadrio-viotti-luchini-2007]. The wall oscillation has also been shown to be effective in reducing the growth rate of the most unstable G$\ddot{\mbox{o}}$rtler vortex developing on a concave surface [@galionis-hall-2005].

An important step towards practical applications of the oscillating-wall technique is the recent finding of a scaling parameter $S$ that is suggested to be related to the amount of drag reduction. This parameter depends on the quantities defining the sinusoidal oscillation, namely the period of oscillation $T$ and 