  The origin of wall shear-stress fluctuations in wall turbulence was studied
through energy dissipation at the wall. While confirming the universality in
wall dissipation at small inner scales, the dissipation at larger scales is a
consequence of near-wall scale interactions. In particular, the energy
transport from the universal small to larger scale strengthens with Reynolds
number due to the growing number of intermediate scales associated with the log
layer. We anticipate that these insights broadly apply to all canonical
wall-bounded turbulence for sufficiently high Reynolds numbers.
