  Wall-resolved large-eddy simulations are performed to study the impact of
spanwise traveling transversal surface waves in zero-pressure gradient
turbulent boundary layer flow. Eighty variations of wavelength, period, and
amplitude of the space- and time-dependent sinusoidal wall motion are
considered for a boundary layer at a momentum thickness based Reynolds number
of $Re_\theta = 1000$. The results show a strong decrease of friction drag of
up to $26\,\%$ and considerable net power saving of up to $10\,\%$. However,
the highest net power saving does not occur at the maximum drag reduction. The
drag reduction is modeled as a function of the actuation parameters by support
vector regression using the LES data.
  A substantial attenuation of the near-wall turbulence intensity and
especially a weakening of the near-wall velocity streaks are observed.
Similarities between the current actuation technique and the method of a
spanwise oscillating wall without any normal surface deflection are reported.
In particular, the generation of a directional spanwise oscillating Stokes
layer is found to be related to skin-friction reduction.
