  Wall-scaled (attached) eddies play a significant role in the overall drag
experienced in high-Reynolds-number turbulent boundary layers (TBLs). This
study aims to delve into the underlying mechanisms driving this phenomenon by
dissecting the active and inactive components of these attached eddies, as
initially proposed by Townsend (1976). Employing a recently introduced
energy-decomposition scheme, we analyze TBL datasets covering a wide range of
Reynolds numbers ($Re_{\tau}$ $\sim$
$\mathcal{O}$(10$^{3}$)--$\mathcal{O}$(10$^{6}$)). This analysis provides
empirical evidence of the distinct contributions of these components to drag
generation, and reveals that while active motions are responsible solely for
generating Reynolds shear stresses, inactive motions are crucial for
transporting streamwise momentum from the logarithmic region to the wall, thus
corroborating earlier hypotheses in the literature.
