Local Balance Unsteady Friction Model

The paper proposes the evaluation of unsteady friction by a one-dimensional local balance model. The model is applied for the case of water hammer in a single pipeline for both the downstream end and upstream end valve, and for both rapid valve closure and opening. The model is based on local balance of the friction force. Comparisons with experimental results show that the model correctly predicts the extreme values of pressure head oscillation, as well as its shape for both rapid valve closure and opening, and then overcomes the limits of previous unsteady friction models based on instantaneous acceleration. As the comparisons with experimental results can be made easily only for pressure oscillations and can be affected by dissipation mechanisms other than friction, the performance of the model is examined also by comparison with the results of a two-dimensional low-Reynolds number k–epsilon model.