Abstract
As a result of our analysis of some facts of turbulent flows, whose explanation is beyond the scope of existing semiempirical theories, in particular, our estimate of the effective roughness height in pipes with distributed roughness characterized by two or more length scales, we present a version of the theory of turbulent flows in channels with smooth and rough walls with a unified mechanism of the dynamic interaction (friction mechanism) of a turbulent flow with its boundaries—the channel walls or external laminar flow. We have derived the expressions for a generalized law of friction that describe a turbulent flow at all admissible Reynolds numbers from the regime of flow with smooth walls to the regime with a complete manifestation of roughness elements and for sand roughness consistent with Nikuradse’s experimental data. One of the conclusions of the theory is the assertion that the only source of turbulence for turbulent flows in channels and jets are the vortices forming near the walls of channels and at the free boundaries of turbulent jets, and only through these vortices is the kinetic energy from the mean flow converted to the energy of turbulent pulsations. The difference between the mechanisms of the laminar and turbulent flow regimes can be clearly represented by Eq. (24).
Published Version
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