  It is well known that in a neutrally-stratified turbulent flow in a deep
constant-stress layer above a flat surface, the variation of the mean velocity
with respect to the distance from the surface obeys the logarithmic law (the
so-called ``law-of-the-wall''). More recently, the same logarithmic law has
been found also in the presence of non flat surfaces. It governs the dynamics
of the mean velocity (i.e. all the smaller scales are averaged out) and
involves renormalized effective parameters. Recent numerical simulations
analyzed by the authors of the present Letter show that a more intrinsic
logarithmic shape actually takes place also at smaller scales. Such a
generalized law-of-the-wall involves effective parameters smoothly depending on
the position along the underlying topography. Here, we present wind tunnel
experimental evidence confirming and corroborating this new-found property. New
results and their physical interpretation are also presented and discussed.
