عنوان مقاله [English]
The sudden changes of boundary conditions in the fluid transmission lines cause a transient flow, which is called water hammer. In this paper, the water hammer resulting from the fast closure of a valve in pipelines is simulated using numerical solution of continuity and Navier-Stokes equations. Simulation has been performed for a high-viscosity oil and for water. The initial flow regime for oil is laminar and for the water is turbulent. The obtained results are compared with the reported experimental data and a good agreement is observed. Velocity contours at different times show two regions with different behavior: the wall region and the pipe core region. In the wall region, the effects of fluid viscosity are dominant, the velocity gradients are sharper, and flow changes more rapidly. While the pipe core region is affected by fluid inertial forces. As the fluid viscosity decreases, the core region becomes more dominant. In addition, a parametric study has been conducted and the effect of different parameters on water hammer has been studied. The results show that by reducing the thickness or length of the pipe, or using a pipe with a lower elastic modulus, the water hammer effects can be significantly reduced. For example, by reducing the length of the pipe from 60 to 18 meters, the maximum pressure decreases by 11%.