  The Kolmogorov flow provides an ideal instance of a virtual channel flow: It
has no boundaries, but nevertheless it possesses well defined mean flow in each
half-wavelength. We exploit this remarkable feature for the purpose of
investigating the interplay between the mean flow and the turbulent drag of the
bulk flow. By means of a set of direct numerical simulations at increasing
Reynolds number we show the dependence of the bulk turbulent drag on the
amplitude of the mean flow. Further, we present a detailed analysis of the
scale-by-scale energy balance, which describes how kinetic energy is
redistributed among different regions of the flow while being transported
toward small dissipative scales. Our results allow us to obtain an accurate
prediction for the spatial energy transport at large scales.
