Velocity Profiles, Unsteady Friction Losses and Transient Modelling

Transient flows in closed-conduits have traditionally been modeled as one-dimensional flows with the assumption that both velocity profiles and friction losses can be accurately predicted on the basis of equivalent steady state (i.e., average) values of velocity. More recently, a host of more complex fluid models have been suggested, but there has been little experimental basis for selecting one model over another. This paper reviews the significance of these questions and briefly overviews various historical approaches that have been proposed for improving the numerical modeling of the fluid structure during transient events. To address the critical need for better data, an experimental set-up in Italy is described and preliminary measurements of velocity profiles during two transient events caused by valve operation are presented.