The Quasi-Steady Quasi-Homogeneous theory describes the dominant mechanism by which the large-scale motions, which are active outside the viscous and buffer layers, affect the turbulent flow inside these layers. The central idea of the QSQH theory is that the near-wall turbulence adjusts itself to the large-scale component of the wall friction. The new formulation of the theory takes into account that the direction of the large-scale component of the wall friction fluctuates. We will show that the effect of these fluctuations is comparable to the effect of the fluctuations of the large-scale component of the longitudinal velocity. In particular, this explains theoretically the known large sensitivity of the fluctuations of longitudinal and spanwise velocities to variations in the Reynolds number in comparison with the sensitivity of the mean velocity profile, the Reynolds stress, and the wall-normal velocity fluctuations.
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