In recent years the increased complexity of pipe systems in both civil and industrial engineering applications determined an intense research activity concerning unsteady-state energy dissipation. In the present paper, attention is focused on laminar transients since they are mathematically tractable as well as there is no influence of the chosen turbulence model. Specifically, comparisons between quasi-2D and ID numerical models are presented along with new laboratory data. Some peculiarities of laminar transients are pointed out with respect to high initial Reynolds number transients. An innovative procedure for evaluating unsteady friction is then proposed and checked.
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