Spatial resolution issues in rough wall turbulence

The question whether spatial resolution effects should be accounted for when performing hot-wire (or particle image velocimetry) measurements in turbulent wall-bounded flows over rough surfaces in the fully rough regime is addressed and answered by exploiting an existing direct numerical simulation database of open-channel flows at Re_τ =500 over a rough surface consisting of randomly distributed roughness elements. The results show sizeable attenuation effects of the streamwise velocity fluctuation intensity, similar to smooth-wall flows with up to 70