Department of Mechanical Engineering,Sharif University of Technology
The condition known as a water-hammer problem is a transient condition that may occur
as a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. The
pressure in the water hammer can vary in such a way that in some cases it may increase and cause
destruction to the hydraulic systems. The pressure in the water hammer can also be decreased to the
extent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid is
vaporized, thus, making a two-phase
ow. This pressure decrease can be as dangerous as the pressure rise.
As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated, which is
referred to as column separation. In almost all standard methods for simulation of column separation,
the steady friction factor was used, but in reality, the quantity of the friction factor is variable. In this
work, the unsteady friction factor has been applied in the Discrete Gas Cavity Model (DGCM), which is
a standard method of column separation prediction. Through comparisons with experimental data, results
showed that applying the unsteady friction factor can improve the magnitude of the predicted duration
shape and the timing of the pressure pulse in all of the case studies.